diff --git a/boot.php b/boot.php
index 3571a77c16..d2597b378e 100644
--- a/boot.php
+++ b/boot.php
@@ -184,79 +184,6 @@ define('TERM_OBJ_POST',  Term::OBJECT_TYPE_POST);
 /** @deprecated since 2019.03, use Term::OBJECT_TYPE_PHOTO instead */
 define('TERM_OBJ_PHOTO', Term::OBJECT_TYPE_PHOTO);
 
-/**
- * @name Namespaces
- *
- * Various namespaces we may need to parse
- * @{
- */
-define('NAMESPACE_ZOT',             'http://purl.org/zot');
-define('NAMESPACE_DFRN',            'http://purl.org/macgirvin/dfrn/1.0');
-define('NAMESPACE_THREAD',          'http://purl.org/syndication/thread/1.0');
-define('NAMESPACE_TOMB',            'http://purl.org/atompub/tombstones/1.0');
-define('NAMESPACE_ACTIVITY2',       'https://www.w3.org/ns/activitystreams#');
-define('NAMESPACE_ACTIVITY',        'http://activitystrea.ms/spec/1.0/');
-define('NAMESPACE_ACTIVITY_SCHEMA', 'http://activitystrea.ms/schema/1.0/');
-define('NAMESPACE_MEDIA',           'http://purl.org/syndication/atommedia');
-define('NAMESPACE_SALMON_ME',       'http://salmon-protocol.org/ns/magic-env');
-define('NAMESPACE_OSTATUSSUB',      'http://ostatus.org/schema/1.0/subscribe');
-define('NAMESPACE_GEORSS',          'http://www.georss.org/georss');
-define('NAMESPACE_POCO',            'http://portablecontacts.net/spec/1.0');
-define('NAMESPACE_FEED',            'http://schemas.google.com/g/2010#updates-from');
-define('NAMESPACE_OSTATUS',         'http://ostatus.org/schema/1.0');
-define('NAMESPACE_STATUSNET',       'http://status.net/schema/api/1/');
-define('NAMESPACE_ATOM1',           'http://www.w3.org/2005/Atom');
-define('NAMESPACE_MASTODON',        'http://mastodon.social/schema/1.0');
-/* @}*/
-
-/**
- * @name Activity
- *
- * Activity stream defines
- * @{
- */
-define('ACTIVITY_LIKE',        NAMESPACE_ACTIVITY_SCHEMA . 'like');
-define('ACTIVITY_DISLIKE',     NAMESPACE_DFRN            . '/dislike');
-define('ACTIVITY_ATTEND',      NAMESPACE_ZOT             . '/activity/attendyes');
-define('ACTIVITY_ATTENDNO',    NAMESPACE_ZOT             . '/activity/attendno');
-define('ACTIVITY_ATTENDMAYBE', NAMESPACE_ZOT             . '/activity/attendmaybe');
-
-define('ACTIVITY_OBJ_HEART',   NAMESPACE_DFRN            . '/heart');
-
-define('ACTIVITY_FRIEND',      NAMESPACE_ACTIVITY_SCHEMA . 'make-friend');
-define('ACTIVITY_REQ_FRIEND',  NAMESPACE_ACTIVITY_SCHEMA . 'request-friend');
-define('ACTIVITY_UNFRIEND',    NAMESPACE_ACTIVITY_SCHEMA . 'remove-friend');
-define('ACTIVITY_FOLLOW',      NAMESPACE_ACTIVITY_SCHEMA . 'follow');
-define('ACTIVITY_UNFOLLOW',    NAMESPACE_ACTIVITY_SCHEMA . 'stop-following');
-define('ACTIVITY_JOIN',        NAMESPACE_ACTIVITY_SCHEMA . 'join');
-
-define('ACTIVITY_POST',        NAMESPACE_ACTIVITY_SCHEMA . 'post');
-define('ACTIVITY_UPDATE',      NAMESPACE_ACTIVITY_SCHEMA . 'update');
-define('ACTIVITY_TAG',         NAMESPACE_ACTIVITY_SCHEMA . 'tag');
-define('ACTIVITY_FAVORITE',    NAMESPACE_ACTIVITY_SCHEMA . 'favorite');
-define('ACTIVITY_UNFAVORITE',  NAMESPACE_ACTIVITY_SCHEMA . 'unfavorite');
-define('ACTIVITY_SHARE',       NAMESPACE_ACTIVITY_SCHEMA . 'share');
-define('ACTIVITY_DELETE',      NAMESPACE_ACTIVITY_SCHEMA . 'delete');
-define('ACTIVITY2_ANNOUNCE',   NAMESPACE_ACTIVITY2       . 'Announce');
-
-define('ACTIVITY_POKE',        NAMESPACE_ZOT . '/activity/poke');
-
-define('ACTIVITY_OBJ_BOOKMARK', NAMESPACE_ACTIVITY_SCHEMA . 'bookmark');
-define('ACTIVITY_OBJ_COMMENT', NAMESPACE_ACTIVITY_SCHEMA . 'comment');
-define('ACTIVITY_OBJ_NOTE',    NAMESPACE_ACTIVITY_SCHEMA . 'note');
-define('ACTIVITY_OBJ_PERSON',  NAMESPACE_ACTIVITY_SCHEMA . 'person');
-define('ACTIVITY_OBJ_IMAGE',   NAMESPACE_ACTIVITY_SCHEMA . 'image');
-define('ACTIVITY_OBJ_PHOTO',   NAMESPACE_ACTIVITY_SCHEMA . 'photo');
-define('ACTIVITY_OBJ_VIDEO',   NAMESPACE_ACTIVITY_SCHEMA . 'video');
-define('ACTIVITY_OBJ_P_PHOTO', NAMESPACE_ACTIVITY_SCHEMA . 'profile-photo');
-define('ACTIVITY_OBJ_ALBUM',   NAMESPACE_ACTIVITY_SCHEMA . 'photo-album');
-define('ACTIVITY_OBJ_EVENT',   NAMESPACE_ACTIVITY_SCHEMA . 'event');
-define('ACTIVITY_OBJ_GROUP',   NAMESPACE_ACTIVITY_SCHEMA . 'group');
-define('ACTIVITY_OBJ_TAGTERM', NAMESPACE_DFRN            . '/tagterm');
-define('ACTIVITY_OBJ_PROFILE', NAMESPACE_DFRN            . '/profile');
-define('ACTIVITY_OBJ_QUESTION', 'http://activityschema.org/object/question');
-/* @}*/
-
 /**
  * @name Gravity
  *
diff --git a/include/api.php b/include/api.php
index 7daf134551..91e31ac945 100644
--- a/include/api.php
+++ b/include/api.php
@@ -41,6 +41,7 @@ use Friendica\Network\HTTPException\NotImplementedException;
 use Friendica\Network\HTTPException\TooManyRequestsException;
 use Friendica\Network\HTTPException\UnauthorizedException;
 use Friendica\Object\Image;
+use Friendica\Protocol\Activity;
 use Friendica\Protocol\Diaspora;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Network;
@@ -2839,19 +2840,19 @@ function api_format_items_activities($item, $type = "json")
 		// get user data and add it to the array of the activity
 		$user = api_get_user($a, $parent_item['author-id']);
 		switch ($parent_item['verb']) {
-			case ACTIVITY_LIKE:
+			case Activity::LIKE:
 				$activities['like'][] = $user;
 				break;
-			case ACTIVITY_DISLIKE:
+			case Activity::DISLIKE:
 				$activities['dislike'][] = $user;
 				break;
-			case ACTIVITY_ATTEND:
+			case Activity::ATTEND:
 				$activities['attendyes'][] = $user;
 				break;
-			case ACTIVITY_ATTENDNO:
+			case Activity::ATTENDNO:
 				$activities['attendno'][] = $user;
 				break;
-			case ACTIVITY_ATTENDMAYBE:
+			case Activity::ATTENDMAYBE:
 				$activities['attendmaybe'][] = $user;
 				break;
 			default:
@@ -5110,7 +5111,7 @@ function api_get_announce($item)
 	}
 
 	$fields = ['author-id', 'author-name', 'author-link', 'author-avatar'];
-	$activity = Item::activityToIndex(ACTIVITY2_ANNOUNCE);
+	$activity = Item::activityToIndex(Activity::ANNOUNCE);
 	$condition = ['parent-uri' => $item['uri'], 'gravity' => GRAVITY_ACTIVITY, 'uid' => [0, $item['uid']], 'activity' => $activity];
 	$announce = Item::selectFirstForUser($item['uid'], $fields, $condition, ['order' => ['received' => true]]);
 	if (!DBA::isResult($announce)) {
diff --git a/include/conversation.php b/include/conversation.php
index 8bcd1b338f..84e47d34e3 100644
--- a/include/conversation.php
+++ b/include/conversation.php
@@ -27,12 +27,12 @@ use Friendica\Model\Term;
 use Friendica\Object\Post;
 use Friendica\Object\Thread;
 use Friendica\Protocol\Activity;
+use Friendica\Util\Crypto;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Proxy as ProxyUtils;
-use Friendica\Util\Temporal;
 use Friendica\Util\Strings;
+use Friendica\Util\Temporal;
 use Friendica\Util\XML;
-use Friendica\Util\Crypto;
 
 function item_extract_images($body) {
 
@@ -145,11 +145,11 @@ function localize_item(&$item)
 	$activity = BaseObject::getClass(Activity::class);
 
 	$xmlhead = "<" . "?xml version='1.0' encoding='UTF-8' ?" . ">";
-	if ($activity->match($item['verb'], ACTIVITY_LIKE)
-		|| $activity->match($item['verb'], ACTIVITY_DISLIKE)
-		|| $activity->match($item['verb'], ACTIVITY_ATTEND)
-		|| $activity->match($item['verb'], ACTIVITY_ATTENDNO)
-		|| $activity->match($item['verb'], ACTIVITY_ATTENDMAYBE)) {
+	if ($activity->match($item['verb'], Activity::LIKE)
+		|| $activity->match($item['verb'], Activity::DISLIKE)
+		|| $activity->match($item['verb'], Activity::ATTEND)
+		|| $activity->match($item['verb'], Activity::ATTENDNO)
+		|| $activity->match($item['verb'], Activity::ATTENDMAYBE)) {
 
 		$fields = ['author-link', 'author-name', 'verb', 'object-type', 'resource-id', 'body', 'plink'];
 		$obj = Item::selectFirst($fields, ['uri' => $item['parent-uri']]);
@@ -161,9 +161,9 @@ function localize_item(&$item)
 		$objauthor =  '[url=' . $obj['author-link'] . ']' . $obj['author-name'] . '[/url]';
 
 		switch ($obj['verb']) {
-			case ACTIVITY_POST:
+			case Activity::POST:
 				switch ($obj['object-type']) {
-					case ACTIVITY_OBJ_EVENT:
+					case Activity\ObjectType::EVENT:
 						$post_type = L10n::t('event');
 						break;
 					default:
@@ -184,24 +184,24 @@ function localize_item(&$item)
 		$plink = '[url=' . $obj['plink'] . ']' . $post_type . '[/url]';
 
 		$bodyverb = '';
-		if ($activity->match($item['verb'], ACTIVITY_LIKE)) {
+		if ($activity->match($item['verb'], Activity::LIKE)) {
 			$bodyverb = L10n::t('%1$s likes %2$s\'s %3$s');
-		} elseif ($activity->match($item['verb'], ACTIVITY_DISLIKE)) {
+		} elseif ($activity->match($item['verb'], Activity::DISLIKE)) {
 			$bodyverb = L10n::t('%1$s doesn\'t like %2$s\'s %3$s');
-		} elseif ($activity->match($item['verb'], ACTIVITY_ATTEND)) {
+		} elseif ($activity->match($item['verb'], Activity::ATTEND)) {
 			$bodyverb = L10n::t('%1$s attends %2$s\'s %3$s');
-		} elseif ($activity->match($item['verb'], ACTIVITY_ATTENDNO)) {
+		} elseif ($activity->match($item['verb'], Activity::ATTENDNO)) {
 			$bodyverb = L10n::t('%1$s doesn\'t attend %2$s\'s %3$s');
-		} elseif ($activity->match($item['verb'], ACTIVITY_ATTENDMAYBE)) {
+		} elseif ($activity->match($item['verb'], Activity::ATTENDMAYBE)) {
 			$bodyverb = L10n::t('%1$s attends maybe %2$s\'s %3$s');
 		}
 
 		$item['body'] = sprintf($bodyverb, $author, $objauthor, $plink);
 	}
 
-	if ($activity->match($item['verb'], ACTIVITY_FRIEND)) {
+	if ($activity->match($item['verb'], Activity::FRIEND)) {
 
-		if ($item['object-type']=="" || $item['object-type']!== ACTIVITY_OBJ_PERSON) return;
+		if ($item['object-type']=="" || $item['object-type']!== Activity\ObjectType::PERSON) return;
 
 		$Aname = $item['author-name'];
 		$Alink = $item['author-link'];
@@ -231,12 +231,12 @@ function localize_item(&$item)
 		$item['body'] = L10n::t('%1$s is now friends with %2$s', $A, $B)."\n\n\n".$Bphoto;
 
 	}
-	if (stristr($item['verb'], ACTIVITY_POKE)) {
+	if (stristr($item['verb'], Activity::POKE)) {
 		$verb = urldecode(substr($item['verb'],strpos($item['verb'],'#')+1));
 		if (!$verb) {
 			return;
 		}
-		if ($item['object-type']=="" || $item['object-type']!== ACTIVITY_OBJ_PERSON) {
+		if ($item['object-type']=="" || $item['object-type']!== Activity\ObjectType::PERSON) {
 			return;
 		}
 
@@ -281,7 +281,7 @@ function localize_item(&$item)
 
 	}
 
-	if ($activity->match($item['verb'], ACTIVITY_TAG)) {
+	if ($activity->match($item['verb'],  Activity::TAG)) {
 		$fields = ['author-id', 'author-link', 'author-name', 'author-network',
 			'verb', 'object-type', 'resource-id', 'body', 'plink'];
 		$obj = Item::selectFirst($fields, ['uri' => $item['parent-uri']]);
@@ -298,9 +298,9 @@ function localize_item(&$item)
 		$objauthor  = '[url=' . Contact::magicLinkByContact($author_arr) . ']' . $obj['author-name'] . '[/url]';
 
 		switch ($obj['verb']) {
-			case ACTIVITY_POST:
+			case Activity::POST:
 				switch ($obj['object-type']) {
-					case ACTIVITY_OBJ_EVENT:
+					case Activity\ObjectType::EVENT:
 						$post_type = L10n::t('event');
 						break;
 					default:
@@ -326,7 +326,7 @@ function localize_item(&$item)
 		$item['body'] = L10n::t('%1$s tagged %2$s\'s %3$s with %4$s', $author, $objauthor, $plink, $tag);
 	}
 
-	if ($activity->match($item['verb'], ACTIVITY_FAVORITE)) {
+	if ($activity->match($item['verb'], Activity::FAVORITE)) {
 		if ($item['object-type'] == "") {
 			return;
 		}
@@ -402,19 +402,15 @@ function visible_activity($item) {
 	/** @var Activity $activity */
 	$activity = BaseObject::getClass(Activity::class);
 
-	/*
-	 * likes (etc.) can apply to other things besides posts. Check if they are post children,
-	 * in which case we handle them specially
-	 */
-	$hidden_activities = [ACTIVITY_LIKE, ACTIVITY_DISLIKE, ACTIVITY_ATTEND, ACTIVITY_ATTENDNO, ACTIVITY_ATTENDMAYBE, ACTIVITY_FOLLOW, ACTIVITY2_ANNOUNCE];
-	foreach ($hidden_activities as $act) {
-		if ($activity->match($item['verb'], $act)) {
-			return false;
-		}
+	if ($activity->isHidden($item['verb'])) {
+		return false;
 	}
 
 	// @TODO below if() block can be rewritten to a single line: $isVisible = allConditionsHere;
-	if ($activity->match($item['verb'], ACTIVITY_FOLLOW) && $item['object-type'] === ACTIVITY_OBJ_NOTE && empty($item['self']) && $item['uid'] == local_user()) {
+	if ($activity->match($item['verb'], Activity::FOLLOW) &&
+	    $item['object-type'] === Activity\ObjectType::NOTE &&
+	    empty($item['self']) &&
+	    $item['uid'] == local_user()) {
 		return false;
 	}
 
@@ -816,7 +812,7 @@ function conversation_fetch_comments($thread_items) {
 	$received = '';
 
 	while ($row = Item::fetch($thread_items)) {
-		if (($row['verb'] == ACTIVITY2_ANNOUNCE) && !empty($row['contact-uid']) && ($row['received'] > $received) && ($row['thr-parent'] == $row['parent-uri'])) {
+		if (($row['verb'] == Activity::ANNOUNCE) && !empty($row['contact-uid']) && ($row['received'] > $received) && ($row['thr-parent'] == $row['parent-uri'])) {
 			$actor = ['link' => $row['author-link'], 'avatar' => $row['author-avatar'], 'name' => $row['author-name']];
 			$received = $row['received'];
 		}
@@ -1008,22 +1004,22 @@ function builtin_activity_puller($item, &$conv_responses) {
 
 		switch ($mode) {
 			case 'like':
-				$verb = ACTIVITY_LIKE;
+				$verb = Activity::LIKE;
 				break;
 			case 'dislike':
-				$verb = ACTIVITY_DISLIKE;
+				$verb = Activity::DISLIKE;
 				break;
 			case 'attendyes':
-				$verb = ACTIVITY_ATTEND;
+				$verb = Activity::ATTEND;
 				break;
 			case 'attendno':
-				$verb = ACTIVITY_ATTENDNO;
+				$verb = Activity::ATTENDNO;
 				break;
 			case 'attendmaybe':
-				$verb = ACTIVITY_ATTENDMAYBE;
+				$verb = Activity::ATTENDMAYBE;
 				break;
 			case 'announce':
-				$verb = ACTIVITY2_ANNOUNCE;
+				$verb = Activity::ANNOUNCE;
 				break;
 			default:
 				return;
@@ -1386,7 +1382,7 @@ function smart_flatten_conversation(array $parent)
 		if (isset($child['children']) && count($child['children'])) {
 			// This helps counting only the regular posts
 			$count_post_closure = function($var) {
-				return $var['verb'] === ACTIVITY_POST;
+				return $var['verb'] === Activity::POST;
 			};
 
 			$child_post_count = count(array_filter($child['children'], $count_post_closure));
@@ -1398,7 +1394,7 @@ function smart_flatten_conversation(array $parent)
 
 				// Searches the post item in the children
 				$j = 0;
-				while($child['children'][$j]['verb'] !== ACTIVITY_POST && $j < count($child['children'])) {
+				while($child['children'][$j]['verb'] !== Activity::POST && $j < count($child['children'])) {
 					$j ++;
 				}
 
diff --git a/include/enotify.php b/include/enotify.php
index 01c946d1ff..a8090e35f8 100644
--- a/include/enotify.php
+++ b/include/enotify.php
@@ -13,6 +13,7 @@ use Friendica\Core\System;
 use Friendica\Database\DBA;
 use Friendica\Model\Item;
 use Friendica\Model\User;
+use Friendica\Protocol\Activity;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Emailer;
 use Friendica\Util\Strings;
@@ -338,7 +339,7 @@ function notification($params)
 		$hsitelink = sprintf($sitelink, '<a href="'.$siteurl.'">'.$sitename.'</a>');
 
 		switch ($params['verb']) {
-			case ACTIVITY_FRIEND:
+			case Activity::FRIEND:
 				// someone started to share with user (mostly OStatus)
 				$subject = L10n::t('[Friendica:Notify] A new person is sharing with you');
 
@@ -348,7 +349,7 @@ function notification($params)
 					$sitename
 				);
 				break;
-			case ACTIVITY_FOLLOW:
+			case Activity::FOLLOW:
 				// someone started to follow the user (mostly OStatus)
 				$subject = L10n::t('[Friendica:Notify] You have a new follower');
 
@@ -385,7 +386,7 @@ function notification($params)
 	}
 
 	if ($params['type'] == NOTIFY_CONFIRM) {
-		if ($params['verb'] == ACTIVITY_FRIEND) { // mutual connection
+		if ($params['verb'] == Activity::FRIEND) { // mutual connection
 			$itemlink =  $params['link'];
 			$subject = L10n::t('[Friendica:Notify] Connection accepted');
 
@@ -821,7 +822,7 @@ function check_item_notification($itemid, $uid, $defaulttype = "") {
 
 		if ($send_notification) {
 			$params["type"] = NOTIFY_SHARE;
-			$params["verb"] = ACTIVITY_TAG;
+			$params["verb"] = Activity::TAG;
 		}
 	}
 
@@ -835,7 +836,7 @@ function check_item_notification($itemid, $uid, $defaulttype = "") {
 
 	if ($item["mention"] || $tagged || ($defaulttype == NOTIFY_TAGSELF)) {
 		$params["type"] = NOTIFY_TAGSELF;
-		$params["verb"] = ACTIVITY_TAG;
+		$params["verb"] = Activity::TAG;
 	}
 
 	// Is it a post that the user had started?
@@ -844,7 +845,7 @@ function check_item_notification($itemid, $uid, $defaulttype = "") {
 
 	if ($thread['mention'] && !$thread['ignored'] && !isset($params["type"])) {
 		$params["type"] = NOTIFY_COMMENT;
-		$params["verb"] = ACTIVITY_POST;
+		$params["verb"] = Activity::POST;
 	}
 
 	// And now we check for participation of one of our contacts in the thread
@@ -852,7 +853,7 @@ function check_item_notification($itemid, $uid, $defaulttype = "") {
 
 	if (!$thread['ignored'] && !isset($params["type"]) && Item::exists($condition)) {
 		$params["type"] = NOTIFY_COMMENT;
-		$params["verb"] = ACTIVITY_POST;
+		$params["verb"] = Activity::POST;
 	}
 
 	if (isset($params["type"])) {
diff --git a/mod/dfrn_confirm.php b/mod/dfrn_confirm.php
index 944ba98be2..c92e5493a1 100644
--- a/mod/dfrn_confirm.php
+++ b/mod/dfrn_confirm.php
@@ -28,6 +28,7 @@ use Friendica\Model\Contact;
 use Friendica\Model\Group;
 use Friendica\Model\User;
 use Friendica\Network\Probe;
+use Friendica\Protocol\Activity;
 use Friendica\Util\Crypto;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Network;
@@ -538,7 +539,7 @@ function dfrn_confirm_post(App $a, $handsfree = null)
 					'source_name'  => ((strlen(stripslashes($combined['name']))) ? stripslashes($combined['name']) : L10n::t('[Name Withheld]')),
 					'source_link'  => $combined['url'],
 					'source_photo' => $combined['photo'],
-					'verb'         => ($mutual?ACTIVITY_FRIEND:ACTIVITY_FOLLOW),
+					'verb'         => ($mutual ? Activity::FRIEND : Activity::FOLLOW),
 					'otype'        => 'intro'
 				]);
 			}
diff --git a/mod/dfrn_request.php b/mod/dfrn_request.php
index f37064573b..a9e17b34b3 100644
--- a/mod/dfrn_request.php
+++ b/mod/dfrn_request.php
@@ -27,6 +27,7 @@ use Friendica\Model\Profile;
 use Friendica\Model\User;
 use Friendica\Module\Login;
 use Friendica\Network\Probe;
+use Friendica\Protocol\Activity;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Network;
 use Friendica\Util\Strings;
@@ -561,7 +562,7 @@ function dfrn_request_content(App $a)
 						'source_name'  => ((strlen(stripslashes($r[0]['name']))) ? stripslashes($r[0]['name']) : L10n::t('[Name Withheld]')),
 						'source_link'  => $r[0]['url'],
 						'source_photo' => $r[0]['photo'],
-						'verb'         => ACTIVITY_REQ_FRIEND,
+						'verb'         => Activity::REQ_FRIEND,
 						'otype'        => 'intro'
 					]);
 				}
diff --git a/mod/item.php b/mod/item.php
index a5875d258b..a96d288193 100644
--- a/mod/item.php
+++ b/mod/item.php
@@ -36,6 +36,7 @@ use Friendica\Model\FileTag;
 use Friendica\Model\Item;
 use Friendica\Model\Photo;
 use Friendica\Model\Term;
+use Friendica\Protocol\Activity;
 use Friendica\Protocol\Diaspora;
 use Friendica\Protocol\Email;
 use Friendica\Util\ACLFormatter;
@@ -133,7 +134,7 @@ function item_post(App $a) {
 		$toplevel_item_id = $toplevel_item['id'];
 		$parent_user = $toplevel_item['uid'];
 
-		$objecttype = ACTIVITY_OBJ_COMMENT;
+		$objecttype = Activity\ObjectType::COMMENT;
 	}
 
 	if ($toplevel_item_id) {
@@ -466,7 +467,7 @@ function item_post(App $a) {
 	$match = null;
 
 	if (!$preview && Photo::setPermissionFromBody($body, $profile_uid, $original_contact_id, $str_contact_allow, $str_group_allow, $str_contact_deny, $str_group_deny)) {
-		$objecttype = ACTIVITY_OBJ_IMAGE;
+		$objecttype = Activity\ObjectType::IMAGE;
 	}
 
 	/*
@@ -502,7 +503,7 @@ function item_post(App $a) {
 	if ((preg_match_all("/\[bookmark\=([^\]]*)\](.*?)\[\/bookmark\]/ism", $body, $match, PREG_SET_ORDER) || isset($data["type"]))
 		&& ($posttype != Item::PT_PERSONAL_NOTE)) {
 		$posttype = Item::PT_PAGE;
-		$objecttype = ACTIVITY_OBJ_BOOKMARK;
+		$objecttype =  Activity\ObjectType::BOOKMARK;
 	}
 
 	/** @var BBCode\Video $bbCodeVideo */
@@ -516,15 +517,15 @@ function item_post(App $a) {
 
 	// Setting the object type if not defined before
 	if (!$objecttype) {
-		$objecttype = ACTIVITY_OBJ_NOTE; // Default value
+		$objecttype = Activity\ObjectType::NOTE; // Default value
 		$objectdata = BBCode::getAttachedData($body);
 
 		if ($objectdata["type"] == "link") {
-			$objecttype = ACTIVITY_OBJ_BOOKMARK;
+			$objecttype = Activity\ObjectType::BOOKMARK;
 		} elseif ($objectdata["type"] == "video") {
-			$objecttype = ACTIVITY_OBJ_VIDEO;
+			$objecttype = Activity\ObjectType::VIDEO;
 		} elseif ($objectdata["type"] == "photo") {
-			$objecttype = ACTIVITY_OBJ_IMAGE;
+			$objecttype = Activity\ObjectType::IMAGE;
 		}
 
 	}
@@ -549,7 +550,7 @@ function item_post(App $a) {
 	}
 
 	if (!strlen($verb)) {
-		$verb = ACTIVITY_POST;
+		$verb = Activity::POST;
 	}
 
 	if ($network == "") {
@@ -761,7 +762,7 @@ function item_post(App $a) {
 				'source_name'  => $datarray['author-name'],
 				'source_link'  => $datarray['author-link'],
 				'source_photo' => $datarray['author-avatar'],
-				'verb'         => ACTIVITY_POST,
+				'verb'         => Activity::POST,
 				'otype'        => 'item',
 				'parent'       => $toplevel_item_id,
 				'parent_uri'   => $toplevel_item['uri']
@@ -781,7 +782,7 @@ function item_post(App $a) {
 				'source_name'  => $datarray['author-name'],
 				'source_link'  => $datarray['author-link'],
 				'source_photo' => $datarray['author-avatar'],
-				'verb'         => ACTIVITY_POST,
+				'verb'         => Activity::POST,
 				'otype'        => 'item'
 			]);
 		}
diff --git a/mod/photos.php b/mod/photos.php
index d89cd04b0b..037da64b10 100644
--- a/mod/photos.php
+++ b/mod/photos.php
@@ -25,6 +25,7 @@ use Friendica\Model\Profile;
 use Friendica\Model\User;
 use Friendica\Network\Probe;
 use Friendica\Object\Image;
+use Friendica\Protocol\Activity;
 use Friendica\Util\ACLFormatter;
 use Friendica\Util\Crypto;
 use Friendica\Util\DateTimeFormat;
@@ -566,24 +567,24 @@ function photos_post(App $a)
 					$arr['deny_cid']      = $photo['deny_cid'];
 					$arr['deny_gid']      = $photo['deny_gid'];
 					$arr['visible']       = 1;
-					$arr['verb']          = ACTIVITY_TAG;
+					$arr['verb']          = Activity::TAG;
 					$arr['gravity']       = GRAVITY_PARENT;
-					$arr['object-type']   = ACTIVITY_OBJ_PERSON;
-					$arr['target-type']   = ACTIVITY_OBJ_IMAGE;
+					$arr['object-type']   = Activity\ObjectType::PERSON;
+					$arr['target-type']   = Activity\ObjectType::IMAGE;
 					$arr['tag']           = $tagged[4];
 					$arr['inform']        = $tagged[2];
 					$arr['origin']        = 1;
 					$arr['body']          = L10n::t('%1$s was tagged in %2$s by %3$s', '[url=' . $tagged[1] . ']' . $tagged[0] . '[/url]', '[url=' . System::baseUrl() . '/photos/' . $owner_record['nickname'] . '/image/' . $photo['resource-id'] . ']' . L10n::t('a photo') . '[/url]', '[url=' . $owner_record['url'] . ']' . $owner_record['name'] . '[/url]') ;
 					$arr['body'] .= "\n\n" . '[url=' . System::baseUrl() . '/photos/' . $owner_record['nickname'] . '/image/' . $photo['resource-id'] . ']' . '[img]' . System::baseUrl() . "/photo/" . $photo['resource-id'] . '-' . $best . '.' . $ext . '[/img][/url]' . "\n" ;
 
-					$arr['object'] = '<object><type>' . ACTIVITY_OBJ_PERSON . '</type><title>' . $tagged[0] . '</title><id>' . $tagged[1] . '/' . $tagged[0] . '</id>';
+					$arr['object'] = '<object><type>' . Activity\ObjectType::PERSON . '</type><title>' . $tagged[0] . '</title><id>' . $tagged[1] . '/' . $tagged[0] . '</id>';
 					$arr['object'] .= '<link>' . XML::escape('<link rel="alternate" type="text/html" href="' . $tagged[1] . '" />' . "\n");
 					if ($tagged[3]) {
 						$arr['object'] .= XML::escape('<link rel="photo" type="' . $photo['type'] . '" href="' . $tagged[3]['photo'] . '" />' . "\n");
 					}
 					$arr['object'] .= '</link></object>' . "\n";
 
-					$arr['target'] = '<target><type>' . ACTIVITY_OBJ_IMAGE . '</type><title>' . $photo['desc'] . '</title><id>'
+					$arr['target'] = '<target><type>' . Activity\ObjectType::IMAGE . '</type><title>' . $photo['desc'] . '</title><id>'
 						. System::baseUrl() . '/photos/' . $owner_record['nickname'] . '/image/' . $photo['resource-id'] . '</id>';
 					$arr['target'] .= '<link>' . XML::escape('<link rel="alternate" type="text/html" href="' . System::baseUrl() . '/photos/' . $owner_record['nickname'] . '/image/' . $photo['resource-id'] . '" />' . "\n" . '<link rel="preview" type="' . $photo['type'] . '" href="' . System::baseUrl() . "/photo/" . $photo['resource-id'] . '-' . $best . '.' . $ext . '" />') . '</link></target>';
 
@@ -1444,11 +1445,11 @@ function photos_content(App $a)
 					$template = $tpl;
 					$sparkle = '';
 
-					/** @var \Friendica\Protocol\Activity $activity */
-					$activity = BaseObject::getClass(\Friendica\Protocol\Activity::class);
+					/** @var Activity $activity */
+					$activity = BaseObject::getClass(Activity::class);
 
-					if (($activity->match($item['verb'], ACTIVITY_LIKE) ||
-					     $activity->match($item['verb'], ACTIVITY_DISLIKE)) &&
+					if (($activity->match($item['verb'], Activity::LIKE) ||
+					     $activity->match($item['verb'], Activity::DISLIKE)) &&
 					    ($item['id'] != $item['parent'])) {
 						continue;
 					}
diff --git a/mod/poke.php b/mod/poke.php
index e8ddf86cd3..69fd42c72c 100644
--- a/mod/poke.php
+++ b/mod/poke.php
@@ -21,6 +21,7 @@ use Friendica\Core\Renderer;
 use Friendica\Core\System;
 use Friendica\Database\DBA;
 use Friendica\Model\Item;
+use Friendica\Protocol\Activity;
 use Friendica\Util\Strings;
 use Friendica\Util\XML;
 
@@ -44,7 +45,7 @@ function poke_init(App $a)
 		return;
 	}
 
-	$activity = ACTIVITY_POKE . '#' . urlencode($verbs[$verb][0]);
+	$activity = Activity::POKE . '#' . urlencode($verbs[$verb][0]);
 
 	$contact_id = intval($_GET['cid']);
 	if (!$contact_id) {
@@ -117,12 +118,12 @@ function poke_init(App $a)
 	$arr['visible']       = 1;
 	$arr['verb']          = $activity;
 	$arr['private']       = $private;
-	$arr['object-type']   = ACTIVITY_OBJ_PERSON;
+	$arr['object-type']   = Activity\ObjectType::PERSON;
 
 	$arr['origin']        = 1;
 	$arr['body']          = '[url=' . $poster['url'] . ']' . $poster['name'] . '[/url]' . ' ' . L10n::t($verbs[$verb][0]) . ' ' . '[url=' . $target['url'] . ']' . $target['name'] . '[/url]';
 
-	$arr['object'] = '<object><type>' . ACTIVITY_OBJ_PERSON . '</type><title>' . $target['name'] . '</title><id>' . $target['url'] . '</id>';
+	$arr['object'] = '<object><type>' . Activity\ObjectType::PERSON . '</type><title>' . $target['name'] . '</title><id>' . $target['url'] . '</id>';
 	$arr['object'] .= '<link>' . XML::escape('<link rel="alternate" type="text/html" href="' . $target['url'] . '" />' . "\n");
 
 	$arr['object'] .= XML::escape('<link rel="photo" type="image/jpeg" href="' . $target['photo'] . '" />' . "\n");
diff --git a/mod/salmon.php b/mod/salmon.php
index 67e467a73f..313c2cb0bb 100644
--- a/mod/salmon.php
+++ b/mod/salmon.php
@@ -2,18 +2,19 @@
 /**
  * @file mod/salmon.php
  */
+
 use Friendica\App;
 use Friendica\Core\Logger;
 use Friendica\Core\PConfig;
 use Friendica\Core\Protocol;
-use Friendica\Core\System;
 use Friendica\Database\DBA;
 use Friendica\Model\Contact;
+use Friendica\Protocol\ActivityNamespace;
 use Friendica\Protocol\OStatus;
 use Friendica\Protocol\Salmon;
 use Friendica\Util\Crypto;
-use Friendica\Util\Strings;
 use Friendica\Util\Network;
+use Friendica\Util\Strings;
 
 function salmon_post(App $a, $xml = '') {
 
@@ -36,7 +37,7 @@ function salmon_post(App $a, $xml = '') {
 
 	// parse the xml
 
-	$dom = simplexml_load_string($xml,'SimpleXMLElement',0,NAMESPACE_SALMON_ME);
+	$dom = simplexml_load_string($xml,'SimpleXMLElement',0, ActivityNamespace::SALMON_ME);
 
 	$base = null;
 
diff --git a/mod/subthread.php b/mod/subthread.php
index 0399ac0cef..aa65b86218 100644
--- a/mod/subthread.php
+++ b/mod/subthread.php
@@ -2,6 +2,7 @@
 /**
  * @file mod/subthread.php
  */
+
 use Friendica\App;
 use Friendica\Core\Hook;
 use Friendica\Core\L10n;
@@ -10,6 +11,7 @@ use Friendica\Core\Session;
 use Friendica\Core\System;
 use Friendica\Database\DBA;
 use Friendica\Model\Item;
+use Friendica\Protocol\Activity;
 use Friendica\Util\Security;
 use Friendica\Util\Strings;
 use Friendica\Util\XML;
@@ -20,7 +22,7 @@ function subthread_content(App $a) {
 		return;
 	}
 
-	$activity = ACTIVITY_FOLLOW;
+	$activity = Activity::FOLLOW;
 
 	$item_id = (($a->argc > 1) ? Strings::escapeTags(trim($a->argv[1])) : 0);
 
@@ -87,7 +89,7 @@ function subthread_content(App $a) {
 	$uri = Item::newURI($owner_uid);
 
 	$post_type = (($item['resource-id']) ? L10n::t('photo') : L10n::t('status'));
-	$objtype = (($item['resource-id']) ? ACTIVITY_OBJ_IMAGE : ACTIVITY_OBJ_NOTE );
+	$objtype = (($item['resource-id']) ? Activity\ObjectType::IMAGE : Activity\ObjectType::NOTE );
 	$link = XML::escape('<link rel="alternate" type="text/html" href="' . System::baseUrl() . '/display/' . $item['guid'] . '" />' . "\n");
 	$body = $item['body'];
 
diff --git a/mod/tagger.php b/mod/tagger.php
index bc8b712970..7532adb3fb 100644
--- a/mod/tagger.php
+++ b/mod/tagger.php
@@ -2,15 +2,17 @@
 /**
  * @file mod/tagger.php
  */
+
 use Friendica\App;
 use Friendica\Core\Hook;
 use Friendica\Core\L10n;
 use Friendica\Core\Logger;
-use Friendica\Core\System;
 use Friendica\Core\Session;
+use Friendica\Core\System;
 use Friendica\Core\Worker;
 use Friendica\Database\DBA;
 use Friendica\Model\Item;
+use Friendica\Protocol\Activity;
 use Friendica\Util\Strings;
 use Friendica\Util\XML;
 use Friendica\Worker\Delivery;
@@ -68,7 +70,7 @@ function tagger_content(App $a) {
 	$uri = Item::newURI($owner_uid);
 	$xterm = XML::escape($term);
 	$post_type = (($item['resource-id']) ? L10n::t('photo') : L10n::t('status'));
-	$targettype = (($item['resource-id']) ? ACTIVITY_OBJ_IMAGE : ACTIVITY_OBJ_NOTE );
+	$targettype = (($item['resource-id']) ? Activity\ObjectType::IMAGE : Activity\ObjectType::NOTE );
 	$href = System::baseUrl() . '/display/' . $item['guid'];
 
 	$link = XML::escape('<link rel="alternate" type="text/html" href="'. $href . '" />' . "\n");
@@ -87,7 +89,7 @@ function tagger_content(App $a) {
 EOT;
 
 	$tagid = System::baseUrl() . '/search?tag=' . $xterm;
-	$objtype = ACTIVITY_OBJ_TAGTERM;
+	$objtype = Activity\ObjectType::TAGTERM;
 
 	$obj = <<< EOT
 	<object>
@@ -130,7 +132,7 @@ EOT;
 	$plink = '[url=' . $item['plink'] . ']' . $post_type . '[/url]';
 	$arr['body'] =  sprintf( $bodyverb, $ulink, $alink, $plink, $termlink );
 
-	$arr['verb'] = ACTIVITY_TAG;
+	$arr['verb'] = Activity::TAG;
 	$arr['target-type'] = $targettype;
 	$arr['target'] = $target;
 	$arr['object-type'] = $objtype;
diff --git a/src/Content/Text/BBCode.php b/src/Content/Text/BBCode.php
index 75f5d506e1..11e7840b0a 100644
--- a/src/Content/Text/BBCode.php
+++ b/src/Content/Text/BBCode.php
@@ -24,6 +24,7 @@ use Friendica\Model\Event;
 use Friendica\Model\Photo;
 use Friendica\Network\Probe;
 use Friendica\Object\Image;
+use Friendica\Protocol\Activity;
 use Friendica\Util\Map;
 use Friendica\Util\Network;
 use Friendica\Util\ParseUrl;
@@ -276,7 +277,7 @@ class BBCode extends BaseObject
 
 			if (preg_match_all("(\[url=(.*?)\]\s*\[img\](.*?)\[\/img\]\s*\[\/url\])ism", $body, $pictures, PREG_SET_ORDER)) {
 				if ((count($pictures) == 1) && !$has_title) {
-					if (!empty($item['object-type']) && ($item['object-type'] == ACTIVITY_OBJ_IMAGE)) {
+					if (!empty($item['object-type']) && ($item['object-type'] == Activity\ObjectType::IMAGE)) {
 						// Replace the preview picture with the real picture
 						$url = str_replace('-1.', '-0.', $pictures[0][2]);
 						$data = ['url' => $url, 'type' => 'photo'];
diff --git a/src/Core/NotificationsManager.php b/src/Core/NotificationsManager.php
index 3c8367c91e..cf2dd9e36d 100644
--- a/src/Core/NotificationsManager.php
+++ b/src/Core/NotificationsManager.php
@@ -12,6 +12,7 @@ use Friendica\Content\Text\HTML;
 use Friendica\Database\DBA;
 use Friendica\Model\Contact;
 use Friendica\Model\Item;
+use Friendica\Protocol\Activity;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Proxy as ProxyUtils;
 use Friendica\Util\Temporal;
@@ -250,7 +251,7 @@ class NotificationsManager extends BaseObject
 
 				// Transform the different types of notification in an usable array
 				switch ($it['verb']) {
-					case ACTIVITY_LIKE:
+					case Activity::LIKE:
 						$notif = [
 							'label' => 'like',
 							'link' => System::baseUrl(true) . '/display/' . $it['parent-guid'],
@@ -263,7 +264,7 @@ class NotificationsManager extends BaseObject
 						];
 						break;
 
-					case ACTIVITY_DISLIKE:
+					case Activity::DISLIKE:
 						$notif = [
 							'label' => 'dislike',
 							'link' => System::baseUrl(true) . '/display/' . $it['parent-guid'],
@@ -276,7 +277,7 @@ class NotificationsManager extends BaseObject
 						];
 						break;
 
-					case ACTIVITY_ATTEND:
+					case Activity::ATTEND:
 						$notif = [
 							'label' => 'attend',
 							'link' => System::baseUrl(true) . '/display/' . $it['parent-guid'],
@@ -289,7 +290,7 @@ class NotificationsManager extends BaseObject
 						];
 						break;
 
-					case ACTIVITY_ATTENDNO:
+					case Activity::ATTENDNO:
 						$notif = [
 							'label' => 'attendno',
 							'link' => System::baseUrl(true) . '/display/' . $it['parent-guid'],
@@ -302,7 +303,7 @@ class NotificationsManager extends BaseObject
 						];
 						break;
 
-					case ACTIVITY_ATTENDMAYBE:
+					case Activity::ATTENDMAYBE:
 						$notif = [
 							'label' => 'attendmaybe',
 							'link' => System::baseUrl(true) . '/display/' . $it['parent-guid'],
@@ -315,7 +316,7 @@ class NotificationsManager extends BaseObject
 						];
 						break;
 
-					case ACTIVITY_FRIEND:
+					case Activity::FRIEND:
 						if (!isset($it['object'])) {
 							$notif = [
 								'label' => 'friend',
diff --git a/src/Model/Contact.php b/src/Model/Contact.php
index 3033bb90b1..c7cfddbb84 100644
--- a/src/Model/Contact.php
+++ b/src/Model/Contact.php
@@ -12,17 +12,17 @@ use Friendica\Core\Hook;
 use Friendica\Core\L10n;
 use Friendica\Core\Logger;
 use Friendica\Core\Protocol;
-use Friendica\Core\System;
 use Friendica\Core\Session;
+use Friendica\Core\System;
 use Friendica\Core\Worker;
 use Friendica\Database\DBA;
 use Friendica\Network\Probe;
 use Friendica\Object\Image;
+use Friendica\Protocol\Activity;
 use Friendica\Protocol\ActivityPub;
 use Friendica\Protocol\DFRN;
 use Friendica\Protocol\Diaspora;
 use Friendica\Protocol\OStatus;
-use Friendica\Protocol\PortableContact;
 use Friendica\Protocol\Salmon;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Network;
@@ -828,7 +828,7 @@ class Contact extends BaseObject
 		} elseif (in_array($protocol, [Protocol::OSTATUS, Protocol::DFRN])) {
 			// create an unfollow slap
 			$item = [];
-			$item['verb'] = NAMESPACE_OSTATUS . "/unfollow";
+			$item['verb'] = Activity::O_UNFOLLOW;
 			$item['follow'] = $contact["url"];
 			$item['body'] = '';
 			$item['title'] = '';
@@ -2366,7 +2366,7 @@ class Contact extends BaseObject
 			if (in_array($protocol, [Protocol::OSTATUS, Protocol::DFRN])) {
 				// create a follow slap
 				$item = [];
-				$item['verb'] = ACTIVITY_FOLLOW;
+				$item['verb'] = Activity::FOLLOW;
 				$item['follow'] = $contact["url"];
 				$item['body'] = '';
 				$item['title'] = '';
@@ -2568,7 +2568,7 @@ class Contact extends BaseObject
 						'source_name'  => ((strlen(stripslashes($contact_record['name']))) ? stripslashes($contact_record['name']) : L10n::t('[Name Withheld]')),
 						'source_link'  => $contact_record['url'],
 						'source_photo' => $contact_record['photo'],
-						'verb'         => ($sharing ? ACTIVITY_FRIEND : ACTIVITY_FOLLOW),
+						'verb'         => ($sharing ? Activity::FRIEND : Activity::FOLLOW),
 						'otype'        => 'intro'
 					]);
 				}
diff --git a/src/Model/Event.php b/src/Model/Event.php
index cbd245a233..fe81a5e958 100644
--- a/src/Model/Event.php
+++ b/src/Model/Event.php
@@ -14,6 +14,7 @@ use Friendica\Core\PConfig;
 use Friendica\Core\Renderer;
 use Friendica\Core\System;
 use Friendica\Database\DBA;
+use Friendica\Protocol\Activity;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Map;
 use Friendica\Util\Strings;
@@ -303,7 +304,7 @@ class Event extends BaseObject
 
 			$item = Item::selectFirst(['id'], ['event-id' => $event['id'], 'uid' => $event['uid']]);
 			if (DBA::isResult($item)) {
-				$object = '<object><type>' . XML::escape(ACTIVITY_OBJ_EVENT) . '</type><title></title><id>' . XML::escape($event['uri']) . '</id>';
+				$object = '<object><type>' . XML::escape(Activity\ObjectType::EVENT) . '</type><title></title><id>' . XML::escape($event['uri']) . '</id>';
 				$object .= '<content>' . XML::escape(self::getBBCode($event)) . '</content>';
 				$object .= '</object>' . "\n";
 
@@ -350,13 +351,13 @@ class Event extends BaseObject
 				$item_arr['deny_gid']      = $event['deny_gid'];
 				$item_arr['private']       = $private;
 				$item_arr['visible']       = 1;
-				$item_arr['verb']          = ACTIVITY_POST;
-				$item_arr['object-type']   = ACTIVITY_OBJ_EVENT;
+				$item_arr['verb']          = Activity::POST;
+				$item_arr['object-type']   = Activity\ObjectType::EVENT;
 				$item_arr['origin']        = $event['cid'] === 0 ? 1 : 0;
 				$item_arr['body']          = self::getBBCode($event);
 				$item_arr['event-id']      = $event['id'];
 
-				$item_arr['object']  = '<object><type>' . XML::escape(ACTIVITY_OBJ_EVENT) . '</type><title></title><id>' . XML::escape($event['uri']) . '</id>';
+				$item_arr['object']  = '<object><type>' . XML::escape(Activity\ObjectType::EVENT) . '</type><title></title><id>' . XML::escape($event['uri']) . '</id>';
 				$item_arr['object'] .= '<content>' . XML::escape(self::getBBCode($event)) . '</content>';
 				$item_arr['object'] .= '</object>' . "\n";
 
diff --git a/src/Model/Item.php b/src/Model/Item.php
index 2c544a263b..9501c8e5d2 100644
--- a/src/Model/Item.php
+++ b/src/Model/Item.php
@@ -97,7 +97,11 @@ class Item extends BaseObject
 
 	// Never reorder or remove entries from this list. Just add new ones at the end, if needed.
 	// The item-activity table only stores the index and needs this array to know the matching activity.
-	const ACTIVITIES = [ACTIVITY_LIKE, ACTIVITY_DISLIKE, ACTIVITY_ATTEND, ACTIVITY_ATTENDNO, ACTIVITY_ATTENDMAYBE, ACTIVITY_FOLLOW, ACTIVITY2_ANNOUNCE];
+	const ACTIVITIES = [
+		Activity::LIKE, Activity::DISLIKE,
+		Activity::ATTEND, Activity::ATTENDNO, Activity::ATTENDMAYBE,
+		Activity::FOLLOW,
+		Activity::ANNOUNCE];
 
 	private static $legacy_mode = null;
 
@@ -210,9 +214,9 @@ class Item extends BaseObject
 				$row['object'] = '';
 			}
 			if (array_key_exists('object-type', $row)) {
-				$row['object-type'] = ACTIVITY_OBJ_NOTE;
+				$row['object-type'] = Activity\ObjectType::NOTE;
 			}
-		} elseif (array_key_exists('verb', $row) && in_array($row['verb'], ['', ACTIVITY_POST, ACTIVITY_SHARE])) {
+		} elseif (array_key_exists('verb', $row) && in_array($row['verb'], ['', Activity::POST, Activity::SHARE])) {
 			// Posts don't have an object or target - but having tags or files.
 			// We safe some performance by building tag and file strings only here.
 			// We remove object and target since they aren't used for this type.
@@ -224,7 +228,7 @@ class Item extends BaseObject
 			}
 		}
 
-		if (!array_key_exists('verb', $row) || in_array($row['verb'], ['', ACTIVITY_POST, ACTIVITY_SHARE])) {
+		if (!array_key_exists('verb', $row) || in_array($row['verb'], ['', Activity::POST, Activity::SHARE])) {
 			// Build the tag string out of the term entries
 			if (array_key_exists('tag', $row) && empty($row['tag'])) {
 				$row['tag'] = Term::tagTextFromItemId($row['internal-iid']);
@@ -1153,14 +1157,14 @@ class Item extends BaseObject
 
 	private static function deleteTagsFromItem($item)
 	{
-		if (($item["verb"] != ACTIVITY_TAG) || ($item["object-type"] != ACTIVITY_OBJ_TAGTERM)) {
+		if (($item["verb"] != Activity::TAG) || ($item["object-type"] != Activity\ObjectType::TAGTERM)) {
 			return;
 		}
 
 		$xo = XML::parseString($item["object"], false);
 		$xt = XML::parseString($item["target"], false);
 
-		if ($xt->type != ACTIVITY_OBJ_NOTE) {
+		if ($xt->type != Activity\ObjectType::NOTE) {
 			return;
 		}
 
@@ -1366,9 +1370,9 @@ class Item extends BaseObject
 			$item['gravity'] = intval($item['gravity']);
 		} elseif ($item['parent-uri'] === $item['uri']) {
 			$item['gravity'] = GRAVITY_PARENT;
-		} elseif ($activity->match($item['verb'], ACTIVITY_POST)) {
+		} elseif ($activity->match($item['verb'], Activity::POST)) {
 			$item['gravity'] = GRAVITY_COMMENT;
-		} elseif ($activity->match($item['verb'], ACTIVITY_FOLLOW)) {
+		} elseif ($activity->match($item['verb'], Activity::FOLLOW)) {
 			$item['gravity'] = GRAVITY_ACTIVITY;
 		} else {
 			$item['gravity'] = GRAVITY_UNKNOWN;   // Should not happen
@@ -1564,14 +1568,14 @@ class Item extends BaseObject
 			return 0;
 		}
 
-		if ($item['verb'] == ACTIVITY_FOLLOW) {
+		if ($item['verb'] == Activity::FOLLOW) {
 			if (!$item['origin'] && ($item['author-id'] == Contact::getPublicIdByUserId($uid))) {
 				// Our own follow request can be relayed to us. We don't store it to avoid notification chaos.
 				Logger::log("Follow: Don't store not origin follow request from us for " . $item['parent-uri'], Logger::DEBUG);
 				return 0;
 			}
 
-			$condition = ['verb' => ACTIVITY_FOLLOW, 'uid' => $item['uid'],
+			$condition = ['verb' => Activity::FOLLOW, 'uid' => $item['uid'],
 				'parent-uri' => $item['parent-uri'], 'author-id' => $item['author-id']];
 			if (self::exists($condition)) {
 				// It happens that we receive multiple follow requests by the same author - we only store one.
@@ -1678,7 +1682,7 @@ class Item extends BaseObject
 			}
 		}
 
-		if (stristr($item['verb'], ACTIVITY_POKE)) {
+		if (stristr($item['verb'], Activity::POKE)) {
 			$notify_type = Delivery::POKE;
 		}
 
@@ -2691,7 +2695,7 @@ class Item extends BaseObject
 		}
 
 		// Only forward posts
-		if ($datarray["verb"] != ACTIVITY_POST) {
+		if ($datarray["verb"] != Activity::POST) {
 			Logger::log('No post', Logger::DEBUG);
 			return false;
 		}
@@ -3044,23 +3048,23 @@ class Item extends BaseObject
 		switch ($verb) {
 			case 'like':
 			case 'unlike':
-				$activity = ACTIVITY_LIKE;
+				$activity = Activity::LIKE;
 				break;
 			case 'dislike':
 			case 'undislike':
-				$activity = ACTIVITY_DISLIKE;
+				$activity = Activity::DISLIKE;
 				break;
 			case 'attendyes':
 			case 'unattendyes':
-				$activity = ACTIVITY_ATTEND;
+				$activity = Activity::ATTEND;
 				break;
 			case 'attendno':
 			case 'unattendno':
-				$activity = ACTIVITY_ATTENDNO;
+				$activity = Activity::ATTENDNO;
 				break;
 			case 'attendmaybe':
 			case 'unattendmaybe':
-				$activity = ACTIVITY_ATTENDMAYBE;
+				$activity = Activity::ATTENDMAYBE;
 				break;
 			default:
 				Logger::log('like: unknown verb ' . $verb . ' for item ' . $item_id);
@@ -3068,7 +3072,7 @@ class Item extends BaseObject
 		}
 
 		// Enable activity toggling instead of on/off
-		$event_verb_flag = $activity === ACTIVITY_ATTEND || $activity === ACTIVITY_ATTENDNO || $activity === ACTIVITY_ATTENDMAYBE;
+		$event_verb_flag = $activity === Activity::ATTEND || $activity === Activity::ATTENDNO || $activity === Activity::ATTENDMAYBE;
 
 		Logger::log('like: verb ' . $verb . ' item ' . $item_id);
 
@@ -3122,7 +3126,7 @@ class Item extends BaseObject
 		// event participation are essentially radio toggles. If you make a subsequent choice,
 		// we need to eradicate your first choice.
 		if ($event_verb_flag) {
-			$verbs = [ACTIVITY_ATTEND, ACTIVITY_ATTENDNO, ACTIVITY_ATTENDMAYBE];
+			$verbs = [Activity::ATTEND, Activity::ATTENDNO, Activity::ATTENDMAYBE];
 
 			// Translate to the index based activity index
 			$activities = [];
@@ -3152,7 +3156,7 @@ class Item extends BaseObject
 			return true;
 		}
 
-		$objtype = $item['resource-id'] ? ACTIVITY_OBJ_IMAGE : ACTIVITY_OBJ_NOTE;
+		$objtype = $item['resource-id'] ? Activity\ObjectType::IMAGE : Activity\ObjectType::NOTE;
 
 		$new_item = [
 			'guid'          => System::createUUID(),
@@ -3318,7 +3322,7 @@ class Item extends BaseObject
 			return L10n::t('event');
 		} elseif (!empty($item['resource-id'])) {
 			return L10n::t('photo');
-		} elseif (!empty($item['verb']) && $item['verb'] !== ACTIVITY_POST) {
+		} elseif (!empty($item['verb']) && $item['verb'] !== Activity::POST) {
 			return L10n::t('activity');
 		} elseif ($item['id'] != $item['parent']) {
 			return L10n::t('comment');
@@ -3432,7 +3436,7 @@ class Item extends BaseObject
 
 		// In order to provide theme developers more possibilities, event items
 		// are treated differently.
-		if ($item['object-type'] === ACTIVITY_OBJ_EVENT && isset($item['event-id'])) {
+		if ($item['object-type'] === Activity\ObjectType::EVENT && isset($item['event-id'])) {
 			$ev = Event::getItemHTML($item);
 			return $ev;
 		}
diff --git a/src/Model/Mail.php b/src/Model/Mail.php
index 96a5493754..e77d147caa 100644
--- a/src/Model/Mail.php
+++ b/src/Model/Mail.php
@@ -13,6 +13,7 @@ use Friendica\Model\Item;
 use Friendica\Model\Photo;
 use Friendica\Database\DBA;
 use Friendica\Network\Probe;
+use Friendica\Protocol\Activity;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Worker\Delivery;
 
@@ -80,7 +81,7 @@ class Mail
 			'source_name' => $msg['from-name'],
 			'source_link' => $msg['from-url'],
 			'source_photo' => $msg['from-photo'],
-			'verb' => ACTIVITY_POST,
+			'verb' => Activity::POST,
 			'otype' => 'mail'
 		];
 
diff --git a/src/Model/Profile.php b/src/Model/Profile.php
index de32903891..eb274a6405 100644
--- a/src/Model/Profile.php
+++ b/src/Model/Profile.php
@@ -23,6 +23,7 @@ use Friendica\Core\System;
 use Friendica\Core\Theme;
 use Friendica\Core\Worker;
 use Friendica\Database\DBA;
+use Friendica\Protocol\Activity;
 use Friendica\Protocol\Diaspora;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Network;
@@ -692,7 +693,7 @@ class Profile
 
 			while ($rr = DBA::fetch($s)) {
 				$condition = ['parent-uri' => $rr['uri'], 'uid' => $rr['uid'], 'author-id' => public_contact(),
-					'activity' => [Item::activityToIndex(ACTIVITY_ATTEND), Item::activityToIndex(ACTIVITY_ATTENDMAYBE)],
+					'activity' => [Item::activityToIndex( Activity::ATTEND), Item::activityToIndex(Activity::ATTENDMAYBE)],
 					'visible' => true, 'deleted' => false];
 				if (!Item::exists($condition)) {
 					continue;
diff --git a/src/Module/Diaspora/Receive.php b/src/Module/Diaspora/Receive.php
index 978bccd833..c787b5f970 100644
--- a/src/Module/Diaspora/Receive.php
+++ b/src/Module/Diaspora/Receive.php
@@ -5,6 +5,7 @@ namespace Friendica\Module\Diaspora;
 use Friendica\App;
 use Friendica\BaseModule;
 use Friendica\Core\Config\Configuration;
+use Friendica\Core\L10n\L10n;
 use Friendica\Model\User;
 use Friendica\Network\HTTPException;
 use Friendica\Protocol\Diaspora;
@@ -34,7 +35,8 @@ class Receive extends BaseModule
 		$enabled = $config->get('system', 'diaspora_enabled', false);
 		if (!$enabled) {
 			self::$logger->info('Diaspora disabled.');
-			throw new HTTPException\InternalServerErrorException('Diaspora disabled.');
+			$l10n = self::getClass(L10n::class);
+			throw new HTTPException\ForbiddenException($l10n->t('Access denied.'));
 		}
 
 		/** @var App\Arguments $args */
diff --git a/src/Module/Xrd.php b/src/Module/Xrd.php
index 5e108c3b53..1028bfd531 100644
--- a/src/Module/Xrd.php
+++ b/src/Module/Xrd.php
@@ -4,11 +4,11 @@ namespace Friendica\Module;
 
 use Friendica\BaseModule;
 use Friendica\Core\Hook;
-use Friendica\Database\DBA;
 use Friendica\Core\Renderer;
-use Friendica\Core\System;
-use Friendica\Model\User;
+use Friendica\Database\DBA;
 use Friendica\Model\Photo;
+use Friendica\Model\User;
+use Friendica\Protocol\ActivityNamespace;
 use Friendica\Protocol\Salmon;
 use Friendica\Util\Strings;
 
@@ -95,11 +95,11 @@ class Xrd extends BaseModule
 			],
 			'links'   => [
 				[
-					'rel'  => NAMESPACE_DFRN,
+					'rel'  => ActivityNamespace::DFRN ,
 					'href' => $owner['url'],
 				],
 				[
-					'rel'  => NAMESPACE_FEED,
+					'rel'  => ActivityNamespace::FEED,
 					'type' => 'application/atom+xml',
 					'href' => $owner['poll'],
 				],
@@ -119,7 +119,7 @@ class Xrd extends BaseModule
 					'href' => $baseURL . '/hcard/' . $owner['nickname'],
 				],
 				[
-					'rel'  => NAMESPACE_POCO,
+					'rel'  => ActivityNamespace::POCO,
 					'href' => $owner['poco'],
 				],
 				[
diff --git a/src/Network/Probe.php b/src/Network/Probe.php
index 946a822da7..80fa641ed4 100644
--- a/src/Network/Probe.php
+++ b/src/Network/Probe.php
@@ -18,11 +18,11 @@ use Friendica\Core\Protocol;
 use Friendica\Core\System;
 use Friendica\Database\DBA;
 use Friendica\Model\Profile;
+use Friendica\Protocol\ActivityNamespace;
 use Friendica\Protocol\ActivityPub;
 use Friendica\Protocol\Email;
 use Friendica\Protocol\Feed;
 use Friendica\Util\Crypto;
-use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Network;
 use Friendica\Util\Strings;
 use Friendica\Util\XML;
@@ -200,10 +200,10 @@ class Probe
 		Logger::log('webfingerDfrn: '.$webbie.':'.print_r($links, true), Logger::DATA);
 		if (!empty($links) && is_array($links)) {
 			foreach ($links as $link) {
-				if ($link['@attributes']['rel'] === NAMESPACE_DFRN) {
+				if ($link['@attributes']['rel'] === ActivityNamespace::DFRN) {
 					$profile_link = $link['@attributes']['href'];
 				}
-				if (($link['@attributes']['rel'] === NAMESPACE_OSTATUSSUB) && ($profile_link == "")) {
+				if (($link['@attributes']['rel'] === ActivityNamespace::OSTATUSSUB) && ($profile_link == "")) {
 					$profile_link = 'stat:'.$link['@attributes']['template'];
 				}
 				if ($link['@attributes']['rel'] === 'http://microformats.org/profile/hcard') {
@@ -492,7 +492,7 @@ class Probe
 		$has_key = false;
 
 		foreach ($webfinger['links'] as $link) {
-			if ($link['rel'] == NAMESPACE_OSTATUSSUB) {
+			if ($link['rel'] == ActivityNamespace::OSTATUSSUB) {
 				$is_ostatus = true;
 			}
 			if ($link['rel'] == 'magic-public-key') {
@@ -955,15 +955,15 @@ class Probe
 		// The array is reversed to take into account the order of preference for same-rel links
 		// See: https://tools.ietf.org/html/rfc7033#section-4.4.4
 		foreach (array_reverse($webfinger["links"]) as $link) {
-			if (($link["rel"] == NAMESPACE_DFRN) && !empty($link["href"])) {
+			if (($link["rel"] == ActivityNamespace::DFRN) && !empty($link["href"])) {
 				$data["network"] = Protocol::DFRN;
-			} elseif (($link["rel"] == NAMESPACE_FEED) && !empty($link["href"])) {
+			} elseif (($link["rel"] == ActivityNamespace::FEED) && !empty($link["href"])) {
 				$data["poll"] = $link["href"];
 			} elseif (($link["rel"] == "http://webfinger.net/rel/profile-page") && (($link["type"] ?? "") == "text/html") && !empty($link["href"])) {
 				$data["url"] = $link["href"];
 			} elseif (($link["rel"] == "http://microformats.org/profile/hcard") && !empty($link["href"])) {
 				$hcard_url = $link["href"];
-			} elseif (($link["rel"] == NAMESPACE_POCO) && !empty($link["href"])) {
+			} elseif (($link["rel"] == ActivityNamespace::POCO) && !empty($link["href"])) {
 				$data["poco"] = $link["href"];
 			} elseif (($link["rel"] == "http://webfinger.net/rel/avatar") && !empty($link["href"])) {
 				$data["photo"] = $link["href"];
@@ -1171,9 +1171,9 @@ class Probe
 				$data["guid"] = $link["href"];
 			} elseif (($link["rel"] == "http://webfinger.net/rel/profile-page") && (($link["type"] ?? "") == "text/html") && !empty($link["href"])) {
 				$data["url"] = $link["href"];
-			} elseif (($link["rel"] == NAMESPACE_FEED) && !empty($link["href"])) {
+			} elseif (($link["rel"] == ActivityNamespace::FEED) && !empty($link["href"])) {
 				$data["poll"] = $link["href"];
-			} elseif (($link["rel"] == NAMESPACE_POCO) && !empty($link["href"])) {
+			} elseif (($link["rel"] == ActivityNamespace::POCO) && !empty($link["href"])) {
 				$data["poco"] = $link["href"];
 			} elseif (($link["rel"] == "salmon") && !empty($link["href"])) {
 				$data["notify"] = $link["href"];
@@ -1273,7 +1273,7 @@ class Probe
 					$data["url"] = $link["href"];
 				} elseif (($link["rel"] == "salmon") && !empty($link["href"])) {
 					$data["notify"] = $link["href"];
-				} elseif (($link["rel"] == NAMESPACE_FEED) && !empty($link["href"])) {
+				} elseif (($link["rel"] == ActivityNamespace::FEED) && !empty($link["href"])) {
 					$data["poll"] = $link["href"];
 				} elseif (($link["rel"] == "magic-public-key") && !empty($link["href"])) {
 					$pubkey = $link["href"];
diff --git a/src/Object/Post.php b/src/Object/Post.php
index 7dd5308017..babf24e0d6 100644
--- a/src/Object/Post.php
+++ b/src/Object/Post.php
@@ -15,8 +15,8 @@ use Friendica\Core\L10n;
 use Friendica\Core\Logger;
 use Friendica\Core\PConfig;
 use Friendica\Core\Protocol;
-use Friendica\Core\Session;
 use Friendica\Core\Renderer;
+use Friendica\Core\Session;
 use Friendica\Database\DBA;
 use Friendica\Model\Contact;
 use Friendica\Model\Item;
@@ -240,7 +240,7 @@ class Post extends BaseObject
 
 		$isevent = false;
 		$attend = [];
-		if ($item['object-type'] === ACTIVITY_OBJ_EVENT) {
+		if ($item['object-type'] === Activity\ObjectType::EVENT) {
 			$response_verbs[] = 'attendyes';
 			$response_verbs[] = 'attendno';
 			$response_verbs[] = 'attendmaybe';
@@ -531,8 +531,8 @@ class Post extends BaseObject
 		 */
 		if ($item->getDataValue('network') === Protocol::MAIL && local_user() != $item->getDataValue('uid')) {
 			return false;
-		} elseif ($activity->match($item->getDataValue('verb'), ACTIVITY_LIKE) ||
-		          $activity->match($item->getDataValue('verb'), ACTIVITY_DISLIKE)) {
+		} elseif ($activity->match($item->getDataValue('verb'), Activity::LIKE) ||
+		          $activity->match($item->getDataValue('verb'), Activity::DISLIKE)) {
 			return false;
 		}
 
diff --git a/src/Object/Thread.php b/src/Object/Thread.php
index 89ed5a9408..4eda1f8f7e 100644
--- a/src/Object/Thread.php
+++ b/src/Object/Thread.php
@@ -7,6 +7,7 @@ namespace Friendica\Object;
 use Friendica\BaseObject;
 use Friendica\Core\Logger;
 use Friendica\Core\Protocol;
+use Friendica\Protocol\Activity;
 use Friendica\Util\Security;
 
 /**
@@ -154,7 +155,7 @@ class Thread extends BaseObject
 			return false;
 		}
 
-		if ($item->getDataValue('verb') === ACTIVITY_LIKE || $item->getDataValue('verb') === ACTIVITY_DISLIKE) {
+		if ($item->getDataValue('verb') === Activity::LIKE || $item->getDataValue('verb') === Activity::DISLIKE) {
 			Logger::log('[WARN] Conversation::addThread : Thread is a (dis)like ('. $item->getId() .').', Logger::DEBUG);
 			return false;
 		}
diff --git a/src/Protocol/Activity.php b/src/Protocol/Activity.php
index 64253b0652..bea2dedb09 100644
--- a/src/Protocol/Activity.php
+++ b/src/Protocol/Activity.php
@@ -2,11 +2,192 @@
 
 namespace Friendica\Protocol;
 
+use Friendica\Protocol\ActivityNamespace;
+
 /**
- * Base class for the Activity namespace
+ * Base class for the Activity Verbs
  */
 final class Activity
 {
+	/**
+	 * Indicates that the actor marked the object as an item of special interest.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#verbs
+	 * @var string
+	 */
+	const LIKE = ActivityNamespace::ACTIVITY_SCHEMA . 'like';
+	/**
+	 * Dislike a message ("I don't like the post")
+	 *
+	 * @see http://purl.org/macgirvin/dfrn/1.0/dislike
+	 * @var string
+	 */
+	const DISLIKE = ActivityNamespace::DFRN . '/dislike';
+
+	/**
+	 * Attend an event
+	 *
+	 * @see https://github.com/friendica/friendica/wiki/ActivityStreams#activity_attend
+	 * @var string
+	 */
+	const ATTEND      = ActivityNamespace::ZOT . '/activity/attendyes';
+	/**
+	 * Don't attend an event
+	 *
+	 * @see https://github.com/friendica/friendica/wiki/ActivityStreams#activity_attendno
+	 * @var string
+	 */
+	const ATTENDNO    = ActivityNamespace::ZOT . '/activity/attendno';
+	/**
+	 * Attend maybe an event
+	 *
+	 * @see https://github.com/friendica/friendica/wiki/ActivityStreams#activity_attendmaybe
+	 * @var string
+	 */
+	const ATTENDMAYBE = ActivityNamespace::ZOT . '/activity/attendmaybe';
+
+	/**
+	 * Indicates the creation of a friendship that is reciprocated by the object.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#verbs
+	 * @var string
+	 */
+	const FRIEND      = ActivityNamespace::ACTIVITY_SCHEMA . 'make-friend';
+	/**
+	 * Indicates the creation of a friendship that has not yet been reciprocated by the object.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#verbs
+	 * @var string
+	 */
+	const REQ_FRIEND = ActivityNamespace::ACTIVITY_SCHEMA . 'request-friend';
+	/**
+	 * Indicates that the actor has removed the object from the collection of friends.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#verbs
+	 * @var string
+	 */
+	const UNFRIEND   = ActivityNamespace::ACTIVITY_SCHEMA . 'remove-friend';
+	/**
+	 * Indicates that the actor began following the activity of the object.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#verbs
+	 * @var string
+	 */
+	const FOLLOW     = ActivityNamespace::ACTIVITY_SCHEMA . 'follow';
+	/**
+	 * Indicates that the actor has stopped following the object.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#verbs
+	 * @var string
+	 */
+	const UNFOLLOW   = ActivityNamespace::ACTIVITY_SCHEMA . 'stop-following';
+	/**
+	 * Indicates that the actor has become a member of the object.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#verbs
+	 * @var string
+	 */
+	const JOIN       = ActivityNamespace::ACTIVITY_SCHEMA . 'join';
+	/**
+	 * Implementors SHOULD use verbs such as post where the actor is adding new items to a collection or similar.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#verbs
+	 * @var string
+	 */
+	const POST       = ActivityNamespace::ACTIVITY_SCHEMA . 'post';
+	/**
+	 * The "update" verb indicates that the actor has modified the object.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#verbs
+	 * @var string
+	 */
+	const UPDATE     = ActivityNamespace::ACTIVITY_SCHEMA . 'update';
+	/**
+	 * Indicates that the actor has identified the presence of a target inside another object.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#verbs
+	 * @var string
+	 */
+	const TAG        = ActivityNamespace::ACTIVITY_SCHEMA . 'tag';
+	/**
+	 * Indicates that the actor marked the object as an item of special interest.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#verbs
+	 * @var string
+	 */
+	const FAVORITE   = ActivityNamespace::ACTIVITY_SCHEMA . 'favorite';
+	/**
+	 * Indicates that the actor has removed the object from the collection of favorited items.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#verbs
+	 * @var string
+	 */
+	const UNFAVORITE = ActivityNamespace::ACTIVITY_SCHEMA . 'unfavorite';
+	/**
+	 * Indicates that the actor has called out the object to readers.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#verbs
+	 * @var string
+	 */
+	const SHARE      = ActivityNamespace::ACTIVITY_SCHEMA . 'share';
+	/**
+	 * Indicates that the actor has deleted the object.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#verbs
+	 * @var string
+	 */
+	const DELETE     = ActivityNamespace::ACTIVITY_SCHEMA . 'delete';
+	/**
+	 * Indicates that the actor is calling the target's attention the object.
+	 *
+	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-announce
+	 * @var string
+	 */
+	const ANNOUNCE   = ActivityNamespace::ACTIVITY2 . 'Announce';
+
+	/**
+	 * Pokes an user.
+	 *
+	 * @see https://github.com/friendica/friendica/wiki/ActivityStreams#activity_poke
+	 * @var string
+	 */
+	const POKE       = ActivityNamespace::ZOT . '/activity/poke';
+
+
+	const O_UNFOLLOW    = ActivityNamespace::OSTATUS . '/unfollow';
+	const O_UNFAVOURITE = ActivityNamespace::OSTATUS . '/unfavorite';
+
+	/**
+	 * likes (etc.) can apply to other things besides posts. Check if they are post children,
+	 * in which case we handle them specially
+	 *
+	 * Hidden activities, which doesn't need to be shown
+	 */
+	const HIDDEN_ACTIVITIES = [
+		Activity::LIKE, Activity::DISLIKE,
+		Activity::ATTEND, Activity::ATTENDNO, Activity::ATTENDMAYBE,
+		Activity::FOLLOW,
+		Activity::ANNOUNCE,
+	];
+
+	/**
+	 * Checks if the given activity is a hidden activity
+	 *
+	 * @param string $activity The current activity
+	 *
+	 * @return bool True, if the activity is hidden
+	 */
+	public function isHidden(string $activity)
+	{
+		foreach (self::HIDDEN_ACTIVITIES as $hiddenActivity) {
+			if ($this->match($activity, $hiddenActivity)) {
+				return true;
+			}
+		}
+
+		return false;
+	}
+
 	/**
 	 * Compare activity uri. Knows about activity namespace.
 	 *
@@ -15,9 +196,10 @@ final class Activity
 	 *
 	 * @return boolean
 	 */
-	public function match(string $haystack, string $needle) {
+	public function match(string $haystack, string $needle)
+	{
 		return (($haystack === $needle) ||
 		        ((basename($needle) === $haystack) &&
-		         strstr($needle, NAMESPACE_ACTIVITY_SCHEMA)));
+		         strstr($needle, ActivityNamespace::ACTIVITY_SCHEMA)));
 	}
 }
diff --git a/src/Protocol/Activity/ObjectType.php b/src/Protocol/Activity/ObjectType.php
new file mode 100644
index 0000000000..313378b3e9
--- /dev/null
+++ b/src/Protocol/Activity/ObjectType.php
@@ -0,0 +1,105 @@
+<?php
+
+namespace Friendica\Protocol\Activity;
+
+use Friendica\Protocol\ActivityNamespace;
+
+/**
+ * This class contains the different object types in activities
+ */
+final class ObjectType
+{
+	/**
+	 * The "bookmark" object type represents a pointer to some URL -- typically a web page.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#bookmark
+	 * @var string
+	 */
+	const BOOKMARK = ActivityNamespace::ACTIVITY_SCHEMA . 'bookmark';
+	/**
+	 * The "comment" object type represents a textual response to another object.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#comment
+	 * @var string
+	 */
+	const COMMENT = ActivityNamespace::ACTIVITY_SCHEMA . 'comment';
+	/**
+	 * The "comment" object type represents a textual response to another object.
+	 * (Default type for items)
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#note
+	 * @var string
+	 */
+	const NOTE = ActivityNamespace::ACTIVITY_SCHEMA . 'note';
+	/**
+	 * The "person" object type represents a user account.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#person
+	 * @var string
+	 */
+	const PERSON = ActivityNamespace::ACTIVITY_SCHEMA . 'person';
+	/**
+	 * The "image" object type represents a graphical image.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#image
+	 * @var string
+	 */
+	const IMAGE = ActivityNamespace::ACTIVITY_SCHEMA . 'image';
+	/**
+	 * @var string
+	 */
+	const PHOTO = ActivityNamespace::ACTIVITY_SCHEMA . 'photo';
+	/**
+	 * The "video" object type represents video content,
+	 * which usually consists of a motion picture track and an audio track.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#video
+	 * @var string
+	 */
+	const VIDEO = ActivityNamespace::ACTIVITY_SCHEMA . 'video';
+	/**
+	 * @var string
+	 */
+	const PROFILE_PHOTO = ActivityNamespace::ACTIVITY_SCHEMA . 'profile-photo';
+	/**
+	 * @var string
+	 */
+	const ALBUM = ActivityNamespace::ACTIVITY_SCHEMA . 'photo-album';
+	/**
+	 * The "event" object type represents an event that occurs in a certain place during a particular interval of time.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#event
+	 * @var string
+	 */
+	const EVENT = ActivityNamespace::ACTIVITY_SCHEMA . 'event';
+	/**
+	 * The "group" object type represents a grouping of objects in which member objects can join or leave.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#group
+	 * @var string
+	 */
+	const GROUP = ActivityNamespace::ACTIVITY_SCHEMA . 'group';
+
+
+	/**
+	 * @var string
+	 */
+	const HEART = ActivityNamespace::DFRN . '/heart';
+	/**
+	 * @var string
+	 */
+	const TAGTERM = ActivityNamespace::DFRN . '/tagterm';
+	/**
+	 * @var string
+	 */
+	const PROFILE = ActivityNamespace::DFRN . '/profile';
+
+
+	/**
+	 * The "question" object type represents a question or poll.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html#question
+	 * @var string
+	 */
+	const QUESTION = 'http://activityschema.org/object/question';
+}
diff --git a/src/Protocol/ActivityNamespace.php b/src/Protocol/ActivityNamespace.php
new file mode 100644
index 0000000000..c504f28339
--- /dev/null
+++ b/src/Protocol/ActivityNamespace.php
@@ -0,0 +1,132 @@
+<?php
+
+namespace Friendica\Protocol;
+
+/**
+ * Activity namespaces constants
+ */
+final class ActivityNamespace
+{
+	/**
+	 * Zot is a WebMTA which provides a decentralised identity and communications protocol using HTTPS/JSON.
+	 *
+	 * @var string
+	 * @see https://zotlabs.org/page/zotlabs/specs+zot6+home
+	 */
+	const ZOT             = 'http://purl.org/zot';
+	/**
+	 * Friendica is using ActivityStreams in version 1.0 for its activities and object types.
+	 * Additional types are used for non standard activities.
+	 *
+	 * @var string
+	 * @see https://github.com/friendica/friendica/wiki/ActivityStreams
+	 */
+	const DFRN            = 'http://purl.org/macgirvin/dfrn/1.0';
+	/**
+	 * This namespace defines an extension for expressing threaded
+	 * discussions within the Atom Syndication Format [RFC4287]
+	 *
+	 * @see https://tools.ietf.org/rfc/rfc4685.txt
+	 * @var string
+	 */
+	const THREAD          = 'http://purl.org/syndication/thread/1.0';
+	/**
+	 * This namespace adds mechanisms to the Atom Syndication Format
+	 * that publishers of Atom Feed and Entry documents can use to
+	 * explicitly identify Atom entries that have been removed.
+	 *
+	 * @see https://tools.ietf.org/html/rfc6721
+	 * @var string
+	 */
+	const TOMB            = 'http://purl.org/atompub/tombstones/1.0';
+	/**
+	 * This specification details a model for representing potential and completed activities
+	 * using the JSON format.
+	 *
+	 * @see https://www.w3.org/ns/activitystreams
+	 * @var string
+	 */
+	const ACTIVITY2       = 'https://www.w3.org/ns/activitystreams#';
+	/**
+	 * Atom Activities 1.0
+	 *
+	 * This namespace presents an XML format that allows activities on social objects
+	 * to be expressed within the Atom Syndication Format.
+	 *
+	 * @see http://activitystrea.ms/spec/1.0
+	 * @var string
+	 */
+	const ACTIVITY        = 'http://activitystrea.ms/spec/1.0/';
+	/**
+	 * This namespace presents a base set of Object types and Verbs for use with Activity Streams.
+	 *
+	 * @see http://activitystrea.ms/head/activity-schema.html
+	 * @var string
+	 */
+	const ACTIVITY_SCHEMA = 'http://activitystrea.ms/schema/1.0/';
+	/**
+	 * Atom Media Extensions
+	 *
+	 * @var string
+	 */
+	const MEDIA           = 'http://purl.org/syndication/atommedia';
+	/**
+	 * The Salmon Protocol is an open, simple, standards-based solution that lets
+	 * aggregators and sources unify the conversations.
+	 *
+	 * @see http://www.salmon-protocol.org/salmon-protocol-summary
+	 * @var string
+	 */
+	const SALMON_ME       = 'http://salmon-protocol.org/ns/magic-env';
+	/**
+	 * OStatus is a minimal specification for distributed status updates or microblogging.
+	 *
+	 * @see https://ostatus.github.io/spec/OStatus%201.0%20Draft%202.html
+	 * @var string
+	 */
+	const OSTATUSSUB      = 'http://ostatus.org/schema/1.0/subscribe';
+	/**
+	 * GeoRSS was designed as a lightweight, community driven way to extend existing feeds with geographic information.
+	 *
+	 * @see http://www.georss.org/
+	 * @var string
+	 */
+	const GEORSS          = 'http://www.georss.org/georss';
+	/**
+	 * The Portable Contacts specification is designed to make it easier for developers
+	 * to give their users a secure way to access the address books and friends lists
+	 * they have built up all over the web.
+	 *
+	 * @see http://portablecontacts.net/draft-spec/
+	 * @var string
+	 */
+	const POCO            = 'http://portablecontacts.net/spec/1.0';
+	/**
+	 * @var string
+	 */
+	const FEED            = 'http://schemas.google.com/g/2010#updates-from';
+	/**
+	 * OStatus is a minimal specification for distributed status updates or microblogging.
+	 *
+	 * @see https://ostatus.github.io/spec/OStatus%201.0%20Draft%202.html
+	 * @var string
+	 */
+	const OSTATUS         = 'http://ostatus.org/schema/1.0';
+	/**
+	 * @var string
+	 */
+	const STATUSNET       = 'http://status.net/schema/api/1/';
+	/**
+	 * This namespace describes the Atom Activity Streams in RDF Vocabulary (AAIR),
+	 * defined as a dictionary of named properties and classes using W3C's RDF technology,
+	 * and specifically a mapping of the Atom Activity Streams work to RDF.
+	 *
+	 * @see http://xmlns.notu.be/aair/#RFC4287
+	 * @var string
+	 */
+	const ATOM1           = 'http://www.w3.org/2005/Atom';
+	/**
+	 * @var string
+	 */
+	const MASTODON        = 'http://mastodon.social/schema/1.0';
+}
diff --git a/src/Protocol/ActivityPub/Processor.php b/src/Protocol/ActivityPub/Processor.php
index 50e8dd91e8..f2b277e44e 100644
--- a/src/Protocol/ActivityPub/Processor.php
+++ b/src/Protocol/ActivityPub/Processor.php
@@ -4,20 +4,21 @@
  */
 namespace Friendica\Protocol\ActivityPub;
 
-use Friendica\Database\DBA;
 use Friendica\Content\Text\BBCode;
 use Friendica\Content\Text\HTML;
 use Friendica\Core\Config;
-use Friendica\Core\PConfig;
 use Friendica\Core\Logger;
+use Friendica\Core\PConfig;
 use Friendica\Core\Protocol;
-use Friendica\Model\Contact;
+use Friendica\Database\DBA;
 use Friendica\Model\APContact;
-use Friendica\Model\Item;
+use Friendica\Model\Contact;
 use Friendica\Model\Event;
+use Friendica\Model\Item;
+use Friendica\Model\Mail;
 use Friendica\Model\Term;
 use Friendica\Model\User;
-use Friendica\Model\Mail;
+use Friendica\Protocol\Activity;
 use Friendica\Protocol\ActivityPub;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\JsonLD;
@@ -167,15 +168,15 @@ class Processor
 	public static function createItem($activity)
 	{
 		$item = [];
-		$item['verb'] = ACTIVITY_POST;
+		$item['verb'] = Activity::POST;
 		$item['thr-parent'] = $activity['reply-to-id'];
 
 		if ($activity['reply-to-id'] == $activity['id']) {
 			$item['gravity'] = GRAVITY_PARENT;
-			$item['object-type'] = ACTIVITY_OBJ_NOTE;
+			$item['object-type'] = Activity\ObjectType::NOTE;
 		} else {
 			$item['gravity'] = GRAVITY_COMMENT;
-			$item['object-type'] = ACTIVITY_OBJ_COMMENT;
+			$item['object-type'] = Activity\ObjectType::COMMENT;
 		}
 
 		if (empty($activity['directmessage']) && ($activity['id'] != $activity['reply-to-id']) && !Item::exists(['uri' => $activity['reply-to-id']])) {
@@ -254,7 +255,7 @@ class Processor
 		$item['verb'] = $verb;
 		$item['thr-parent'] = $activity['object_id'];
 		$item['gravity'] = GRAVITY_ACTIVITY;
-		$item['object-type'] = ACTIVITY_OBJ_NOTE;
+		$item['object-type'] = Activity\ObjectType::NOTE;
 
 		$item['diaspora_signed_text'] = $activity['diaspora:like'] ?? '';
 
diff --git a/src/Protocol/ActivityPub/Receiver.php b/src/Protocol/ActivityPub/Receiver.php
index f23269615e..1bc6f90415 100644
--- a/src/Protocol/ActivityPub/Receiver.php
+++ b/src/Protocol/ActivityPub/Receiver.php
@@ -12,6 +12,7 @@ use Friendica\Model\APContact;
 use Friendica\Model\Conversation;
 use Friendica\Model\Item;
 use Friendica\Model\User;
+use Friendica\Protocol\Activity;
 use Friendica\Protocol\ActivityPub;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\HTTPSignature;
@@ -400,26 +401,26 @@ class Receiver
 						$announce_object_data['object_id'] = $object_data['object_id'];
 						$announce_object_data['object_type'] = $object_data['object_type'];
 
-						ActivityPub\Processor::createActivity($announce_object_data, ACTIVITY2_ANNOUNCE);
+						ActivityPub\Processor::createActivity($announce_object_data, Activity::ANNOUNCE);
 					}
 				}
 				break;
 
 			case 'as:Like':
 				if (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
-					ActivityPub\Processor::createActivity($object_data, ACTIVITY_LIKE);
+					ActivityPub\Processor::createActivity($object_data, Activity::LIKE);
 				}
 				break;
 
 			case 'as:Dislike':
 				if (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
-					ActivityPub\Processor::createActivity($object_data, ACTIVITY_DISLIKE);
+					ActivityPub\Processor::createActivity($object_data, Activity::DISLIKE);
 				}
 				break;
 
 			case 'as:TentativeAccept':
 				if (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
-					ActivityPub\Processor::createActivity($object_data, ACTIVITY_ATTENDMAYBE);
+					ActivityPub\Processor::createActivity($object_data, Activity::ATTENDMAYBE);
 				}
 				break;
 
@@ -444,7 +445,7 @@ class Receiver
 					ActivityPub\Processor::followUser($object_data);
 				} elseif (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
 					$object_data['reply-to-id'] = $object_data['object_id'];
-					ActivityPub\Processor::createActivity($object_data, ACTIVITY_FOLLOW);
+					ActivityPub\Processor::createActivity($object_data, Activity::FOLLOW);
 				}
 				break;
 
@@ -452,7 +453,7 @@ class Receiver
 				if ($object_data['object_type'] == 'as:Follow') {
 					ActivityPub\Processor::acceptFollowUser($object_data);
 				} elseif (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
-					ActivityPub\Processor::createActivity($object_data, ACTIVITY_ATTEND);
+					ActivityPub\Processor::createActivity($object_data, Activity::ATTEND);
 				}
 				break;
 
@@ -460,7 +461,7 @@ class Receiver
 				if ($object_data['object_type'] == 'as:Follow') {
 					ActivityPub\Processor::rejectFollowUser($object_data);
 				} elseif (in_array($object_data['object_type'], self::CONTENT_TYPES)) {
-					ActivityPub\Processor::createActivity($object_data, ACTIVITY_ATTENDNO);
+					ActivityPub\Processor::createActivity($object_data, Activity::ATTENDNO);
 				}
 				break;
 
diff --git a/src/Protocol/ActivityPub/Transmitter.php b/src/Protocol/ActivityPub/Transmitter.php
index d2581ff3f4..531b4c6621 100644
--- a/src/Protocol/ActivityPub/Transmitter.php
+++ b/src/Protocol/ActivityPub/Transmitter.php
@@ -10,6 +10,7 @@ use Friendica\Database\DBA;
 use Friendica\Core\Config;
 use Friendica\Core\Logger;
 use Friendica\Core\System;
+use Friendica\Protocol\Activity;
 use Friendica\Util\HTTPSignature;
 use Friendica\Core\Protocol;
 use Friendica\Model\Conversation;
@@ -761,25 +762,25 @@ class Transmitter
 
 		if ($reshared) {
 			$type = 'Announce';
-		} elseif ($item['verb'] == ACTIVITY_POST) {
+		} elseif ($item['verb'] == Activity::POST) {
 			if ($item['created'] == $item['edited']) {
 				$type = 'Create';
 			} else {
 				$type = 'Update';
 			}
-		} elseif ($item['verb'] == ACTIVITY_LIKE) {
+		} elseif ($item['verb'] == Activity::LIKE) {
 			$type = 'Like';
-		} elseif ($item['verb'] == ACTIVITY_DISLIKE) {
+		} elseif ($item['verb'] == Activity::DISLIKE) {
 			$type = 'Dislike';
-		} elseif ($item['verb'] == ACTIVITY_ATTEND) {
+		} elseif ($item['verb'] == Activity::ATTEND) {
 			$type = 'Accept';
-		} elseif ($item['verb'] == ACTIVITY_ATTENDNO) {
+		} elseif ($item['verb'] == Activity::ATTENDNO) {
 			$type = 'Reject';
-		} elseif ($item['verb'] == ACTIVITY_ATTENDMAYBE) {
+		} elseif ($item['verb'] == Activity::ATTENDMAYBE) {
 			$type = 'TentativeAccept';
-		} elseif ($item['verb'] == ACTIVITY_FOLLOW) {
+		} elseif ($item['verb'] == Activity::FOLLOW) {
 			$type = 'Follow';
-		} elseif ($item['verb'] == ACTIVITY_TAG) {
+		} elseif ($item['verb'] == Activity::TAG) {
 			$type = 'Add';
 		} else {
 			$type = '';
@@ -1571,7 +1572,7 @@ class Transmitter
 			$uid = $first_user['uid'];
 		}
 
-		$condition = ['verb' => ACTIVITY_FOLLOW, 'uid' => 0, 'parent-uri' => $object,
+		$condition = ['verb' => Activity::FOLLOW, 'uid' => 0, 'parent-uri' => $object,
 			'author-id' => Contact::getPublicIdByUserId($uid)];
 		if (Item::exists($condition)) {
 			Logger::log('Follow for ' . $object . ' for user ' . $uid . ' does already exist.', Logger::DEBUG);
diff --git a/src/Protocol/DFRN.php b/src/Protocol/DFRN.php
index e1901011e1..2016c7339d 100644
--- a/src/Protocol/DFRN.php
+++ b/src/Protocol/DFRN.php
@@ -10,7 +10,6 @@ namespace Friendica\Protocol;
 
 use DOMDocument;
 use DOMXPath;
-use Friendica\App;
 use Friendica\App\BaseURL;
 use Friendica\BaseObject;
 use Friendica\Content\OEmbed;
@@ -21,7 +20,6 @@ use Friendica\Core\Hook;
 use Friendica\Core\Logger;
 use Friendica\Core\Protocol;
 use Friendica\Core\System;
-use Friendica\Core\Session;
 use Friendica\Database\DBA;
 use Friendica\Model\Contact;
 use Friendica\Model\Conversation;
@@ -34,6 +32,7 @@ use Friendica\Model\Profile;
 use Friendica\Model\User;
 use Friendica\Network\Probe;
 use Friendica\Object\Image;
+use Friendica\Protocol\ActivityNamespace;
 use Friendica\Util\Crypto;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Network;
@@ -382,18 +381,18 @@ class DFRN
 		$type = 'html';
 
 		if ($conversation) {
-			$root = $doc->createElementNS(NAMESPACE_ATOM1, 'feed');
+			$root = $doc->createElementNS(ActivityNamespace::ATOM1, 'feed');
 			$doc->appendChild($root);
 
-			$root->setAttribute("xmlns:thr", NAMESPACE_THREAD);
-			$root->setAttribute("xmlns:at", NAMESPACE_TOMB);
-			$root->setAttribute("xmlns:media", NAMESPACE_MEDIA);
-			$root->setAttribute("xmlns:dfrn", NAMESPACE_DFRN);
-			$root->setAttribute("xmlns:activity", NAMESPACE_ACTIVITY);
-			$root->setAttribute("xmlns:georss", NAMESPACE_GEORSS);
-			$root->setAttribute("xmlns:poco", NAMESPACE_POCO);
-			$root->setAttribute("xmlns:ostatus", NAMESPACE_OSTATUS);
-			$root->setAttribute("xmlns:statusnet", NAMESPACE_STATUSNET);
+			$root->setAttribute("xmlns:thr", ActivityNamespace::THREAD);
+			$root->setAttribute("xmlns:at", ActivityNamespace::TOMB);
+			$root->setAttribute("xmlns:media", ActivityNamespace::MEDIA);
+			$root->setAttribute("xmlns:dfrn", ActivityNamespace::DFRN);
+			$root->setAttribute("xmlns:activity", ActivityNamespace::ACTIVITY);
+			$root->setAttribute("xmlns:georss", ActivityNamespace::GEORSS);
+			$root->setAttribute("xmlns:poco", ActivityNamespace::POCO);
+			$root->setAttribute("xmlns:ostatus", ActivityNamespace::OSTATUS);
+			$root->setAttribute("xmlns:statusnet", ActivityNamespace::STATUSNET);
 
 			//$root = self::addHeader($doc, $owner, "dfrn:owner", "", false);
 
@@ -557,18 +556,18 @@ class DFRN
 			$alternatelink = $owner['url'];
 		}
 
-		$root = $doc->createElementNS(NAMESPACE_ATOM1, 'feed');
+		$root = $doc->createElementNS(ActivityNamespace::ATOM1, 'feed');
 		$doc->appendChild($root);
 
-		$root->setAttribute("xmlns:thr", NAMESPACE_THREAD);
-		$root->setAttribute("xmlns:at", NAMESPACE_TOMB);
-		$root->setAttribute("xmlns:media", NAMESPACE_MEDIA);
-		$root->setAttribute("xmlns:dfrn", NAMESPACE_DFRN);
-		$root->setAttribute("xmlns:activity", NAMESPACE_ACTIVITY);
-		$root->setAttribute("xmlns:georss", NAMESPACE_GEORSS);
-		$root->setAttribute("xmlns:poco", NAMESPACE_POCO);
-		$root->setAttribute("xmlns:ostatus", NAMESPACE_OSTATUS);
-		$root->setAttribute("xmlns:statusnet", NAMESPACE_STATUSNET);
+		$root->setAttribute("xmlns:thr", ActivityNamespace::THREAD);
+		$root->setAttribute("xmlns:at", ActivityNamespace::TOMB);
+		$root->setAttribute("xmlns:media", ActivityNamespace::MEDIA);
+		$root->setAttribute("xmlns:dfrn", ActivityNamespace::DFRN);
+		$root->setAttribute("xmlns:activity", ActivityNamespace::ACTIVITY);
+		$root->setAttribute("xmlns:georss", ActivityNamespace::GEORSS);
+		$root->setAttribute("xmlns:poco", ActivityNamespace::POCO);
+		$root->setAttribute("xmlns:ostatus", ActivityNamespace::OSTATUS);
+		$root->setAttribute("xmlns:statusnet", ActivityNamespace::STATUSNET);
 
 		XML::addElement($doc, $root, "id", System::baseUrl()."/profile/".$owner["nick"]);
 		XML::addElement($doc, $root, "title", $owner["name"]);
@@ -941,18 +940,18 @@ class DFRN
 		if (!$single) {
 			$entry = $doc->createElement("entry");
 		} else {
-			$entry = $doc->createElementNS(NAMESPACE_ATOM1, 'entry');
+			$entry = $doc->createElementNS(ActivityNamespace::ATOM1, 'entry');
 			$doc->appendChild($entry);
 
-			$entry->setAttribute("xmlns:thr", NAMESPACE_THREAD);
-			$entry->setAttribute("xmlns:at", NAMESPACE_TOMB);
-			$entry->setAttribute("xmlns:media", NAMESPACE_MEDIA);
-			$entry->setAttribute("xmlns:dfrn", NAMESPACE_DFRN);
-			$entry->setAttribute("xmlns:activity", NAMESPACE_ACTIVITY);
-			$entry->setAttribute("xmlns:georss", NAMESPACE_GEORSS);
-			$entry->setAttribute("xmlns:poco", NAMESPACE_POCO);
-			$entry->setAttribute("xmlns:ostatus", NAMESPACE_OSTATUS);
-			$entry->setAttribute("xmlns:statusnet", NAMESPACE_STATUSNET);
+			$entry->setAttribute("xmlns:thr", ActivityNamespace::THREAD);
+			$entry->setAttribute("xmlns:at", ActivityNamespace::TOMB);
+			$entry->setAttribute("xmlns:media", ActivityNamespace::MEDIA);
+			$entry->setAttribute("xmlns:dfrn", ActivityNamespace::DFRN);
+			$entry->setAttribute("xmlns:activity", ActivityNamespace::ACTIVITY);
+			$entry->setAttribute("xmlns:georss", ActivityNamespace::GEORSS);
+			$entry->setAttribute("xmlns:poco", ActivityNamespace::POCO);
+			$entry->setAttribute("xmlns:ostatus", ActivityNamespace::OSTATUS);
+			$entry->setAttribute("xmlns:statusnet", ActivityNamespace::STATUSNET);
 		}
 
 		if ($item['private']) {
@@ -1079,9 +1078,9 @@ class DFRN
 		if ($item['object-type'] != "") {
 			XML::addElement($doc, $entry, "activity:object-type", $item['object-type']);
 		} elseif ($item['id'] == $item['parent']) {
-			XML::addElement($doc, $entry, "activity:object-type", ACTIVITY_OBJ_NOTE);
+			XML::addElement($doc, $entry, "activity:object-type", Activity\ObjectType::NOTE);
 		} else {
-			XML::addElement($doc, $entry, "activity:object-type", ACTIVITY_OBJ_COMMENT);
+			XML::addElement($doc, $entry, "activity:object-type", Activity\ObjectType::COMMENT);
 		}
 
 		$actobj = self::createActivity($doc, "activity:object", $item['object']);
@@ -1124,7 +1123,7 @@ class DFRN
 					"link",
 					"",
 					["rel" => "mentioned",
-							"ostatus:object-type" => ACTIVITY_OBJ_GROUP,
+							"ostatus:object-type" => Activity\ObjectType::GROUP,
 							"href" => $mention]
 				);
 			} else {
@@ -1134,7 +1133,7 @@ class DFRN
 					"link",
 					"",
 					["rel" => "mentioned",
-							"ostatus:object-type" => ACTIVITY_OBJ_PERSON,
+							"ostatus:object-type" => Activity\ObjectType::PERSON,
 							"href" => $mention]
 				);
 			}
@@ -1750,7 +1749,7 @@ class DFRN
 		$obj_doc = new DOMDocument("1.0", "utf-8");
 		$obj_doc->formatOutput = true;
 
-		$obj_element = $obj_doc->createElementNS(NAMESPACE_ATOM1, $element);
+		$obj_element = $obj_doc->createElementNS( ActivityNamespace::ATOM1, $element);
 
 		$activity_type = $xpath->query("activity:object-type/text()", $activity)->item(0)->nodeValue;
 		XML::addElement($obj_doc, $obj_element, "type", $activity_type);
@@ -1907,7 +1906,7 @@ class DFRN
 				'source_name'  => $importer['name'],
 				'source_link'  => $importer['url'],
 				'source_photo' => $importer['photo'],
-				'verb'         => ACTIVITY_REQ_FRIEND,
+				'verb'         => Activity::REQ_FRIEND,
 				'otype'        => 'intro']
 		);
 
@@ -2117,7 +2116,7 @@ class DFRN
 		}
 		$xo = XML::parseString($item["object"], false);
 
-		if (($xo->type == ACTIVITY_OBJ_PERSON) && ($xo->id)) {
+		if (($xo->type == Activity\ObjectType::PERSON) && ($xo->id)) {
 			// somebody was poked/prodded. Was it me?
 			$Blink = '';
 			foreach ($xo->link as $l) {
@@ -2186,32 +2185,32 @@ class DFRN
 
 			// Big question: Do we need these functions? They were part of the "consume_feed" function.
 			// This function once was responsible for DFRN and OStatus.
-			if ($activity->match($item["verb"], ACTIVITY_FOLLOW)) {
+			if ($activity->match($item["verb"], Activity::FOLLOW)) {
 				Logger::log("New follower");
 				Contact::addRelationship($importer, $contact, $item);
 				return false;
 			}
-			if ($activity->match($item["verb"], ACTIVITY_UNFOLLOW)) {
+			if ($activity->match($item["verb"], Activity::UNFOLLOW)) {
 				Logger::log("Lost follower");
 				Contact::removeFollower($importer, $contact, $item);
 				return false;
 			}
-			if ($activity->match($item["verb"], ACTIVITY_REQ_FRIEND)) {
+			if ($activity->match($item["verb"], Activity::REQ_FRIEND)) {
 				Logger::log("New friend request");
 				Contact::addRelationship($importer, $contact, $item, true);
 				return false;
 			}
-			if ($activity->match($item["verb"], ACTIVITY_UNFRIEND)) {
+			if ($activity->match($item["verb"], Activity::UNFRIEND)) {
 				Logger::log("Lost sharer");
 				Contact::removeSharer($importer, $contact, $item);
 				return false;
 			}
 		} else {
-			if (($item["verb"] == ACTIVITY_LIKE)
-				|| ($item["verb"] == ACTIVITY_DISLIKE)
-				|| ($item["verb"] == ACTIVITY_ATTEND)
-				|| ($item["verb"] == ACTIVITY_ATTENDNO)
-				|| ($item["verb"] == ACTIVITY_ATTENDMAYBE)
+			if (($item["verb"] == Activity::LIKE)
+				|| ($item["verb"] == Activity::DISLIKE)
+				|| ($item["verb"] == Activity::ATTEND)
+				|| ($item["verb"] == Activity::ATTENDNO)
+				|| ($item["verb"] == Activity::ATTENDMAYBE)
 			) {
 				$is_like = true;
 				$item["gravity"] = GRAVITY_ACTIVITY;
@@ -2238,11 +2237,11 @@ class DFRN
 				$is_like = false;
 			}
 
-			if (($item["verb"] == ACTIVITY_TAG) && ($item["object-type"] == ACTIVITY_OBJ_TAGTERM)) {
+			if (($item["verb"] == Activity::TAG) && ($item["object-type"] == Activity\ObjectType::TAGTERM)) {
 				$xo = XML::parseString($item["object"], false);
 				$xt = XML::parseString($item["target"], false);
 
-				if ($xt->type == ACTIVITY_OBJ_NOTE) {
+				if ($xt->type == Activity\ObjectType::NOTE) {
 					$item_tag = Item::selectFirst(['id', 'tag'], ['uri' => $xt->id, 'uid' => $importer["importer_uid"]]);
 
 					if (!DBA::isResult($item_tag)) {
@@ -2517,7 +2516,7 @@ class DFRN
 		// Now assign the rest of the values that depend on the type of the message
 		if (in_array($entrytype, [DFRN::REPLY, DFRN::REPLY_RC])) {
 			if (!isset($item["object-type"])) {
-				$item["object-type"] = ACTIVITY_OBJ_COMMENT;
+				$item["object-type"] = Activity\ObjectType::COMMENT;
 			}
 
 			if ($item["contact-id"] != $owner["contact-id"]) {
@@ -2541,11 +2540,11 @@ class DFRN
 			$item["wall"] = 1;
 		} elseif ($entrytype == DFRN::TOP_LEVEL) {
 			if (!isset($item["object-type"])) {
-				$item["object-type"] = ACTIVITY_OBJ_NOTE;
+				$item["object-type"] = Activity\ObjectType::NOTE;
 			}
 
 			// Is it an event?
-			if (($item["object-type"] == ACTIVITY_OBJ_EVENT) && !$owner_unknown) {
+			if (($item["object-type"] == Activity\ObjectType::EVENT) && !$owner_unknown) {
 				Logger::log("Item ".$item["uri"]." seems to contain an event.", Logger::DEBUG);
 				$ev = Event::fromBBCode($item["body"]);
 				if ((!empty($ev['desc']) || !empty($ev['summary'])) && !empty($ev['start'])) {
@@ -2642,7 +2641,7 @@ class DFRN
 				Item::distribute($posted_id);
 			}
 
-			if (stristr($item["verb"], ACTIVITY_POKE)) {
+			if (stristr($item["verb"], Activity::POKE)) {
 				$item['id'] = $posted_id;
 				self::doPoke($item, $importer);
 			}
@@ -2731,16 +2730,16 @@ class DFRN
 		@$doc->loadXML($xml);
 
 		$xpath = new DOMXPath($doc);
-		$xpath->registerNamespace("atom", NAMESPACE_ATOM1);
-		$xpath->registerNamespace("thr", NAMESPACE_THREAD);
-		$xpath->registerNamespace("at", NAMESPACE_TOMB);
-		$xpath->registerNamespace("media", NAMESPACE_MEDIA);
-		$xpath->registerNamespace("dfrn", NAMESPACE_DFRN);
-		$xpath->registerNamespace("activity", NAMESPACE_ACTIVITY);
-		$xpath->registerNamespace("georss", NAMESPACE_GEORSS);
-		$xpath->registerNamespace("poco", NAMESPACE_POCO);
-		$xpath->registerNamespace("ostatus", NAMESPACE_OSTATUS);
-		$xpath->registerNamespace("statusnet", NAMESPACE_STATUSNET);
+		$xpath->registerNamespace("atom", ActivityNamespace::ATOM1);
+		$xpath->registerNamespace("thr", ActivityNamespace::THREAD);
+		$xpath->registerNamespace("at", ActivityNamespace::TOMB);
+		$xpath->registerNamespace("media", ActivityNamespace::MEDIA);
+		$xpath->registerNamespace("dfrn", ActivityNamespace::DFRN);
+		$xpath->registerNamespace("activity", ActivityNamespace::ACTIVITY);
+		$xpath->registerNamespace("georss", ActivityNamespace::GEORSS);
+		$xpath->registerNamespace("poco", ActivityNamespace::POCO);
+		$xpath->registerNamespace("ostatus", ActivityNamespace::OSTATUS);
+		$xpath->registerNamespace("statusnet", ActivityNamespace::STATUSNET);
 
 		$header = [];
 		$header["uid"] = $importer["importer_uid"];
@@ -2865,7 +2864,7 @@ class DFRN
 		if ($item['verb']) {
 			return $item['verb'];
 		}
-		return ACTIVITY_POST;
+		return Activity::POST;
 	}
 
 	private static function tgroupCheck($uid, $item)
diff --git a/src/Protocol/Diaspora.php b/src/Protocol/Diaspora.php
index aec3a283f8..dc02366cb1 100644
--- a/src/Protocol/Diaspora.php
+++ b/src/Protocol/Diaspora.php
@@ -32,6 +32,7 @@ use Friendica\Model\Mail;
 use Friendica\Model\Profile;
 use Friendica\Model\User;
 use Friendica\Network\Probe;
+use Friendica\Protocol\ActivityNamespace;
 use Friendica\Util\Crypto;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Map;
@@ -465,7 +466,7 @@ class Diaspora
 			}
 		}
 
-		$base = $basedom->children(NAMESPACE_SALMON_ME);
+		$base = $basedom->children(ActivityNamespace::SALMON_ME);
 
 		// Not sure if this cleaning is needed
 		$data = str_replace([" ", "\t", "\r", "\n"], ["", "", "", ""], $base->data);
@@ -577,7 +578,7 @@ class Diaspora
 			$author_link = str_replace('acct:', '', $idom->author_id);
 		}
 
-		$dom = $basedom->children(NAMESPACE_SALMON_ME);
+		$dom = $basedom->children(ActivityNamespace::SALMON_ME);
 
 		// figure out where in the DOM tree our data is hiding
 
@@ -1845,7 +1846,7 @@ class Diaspora
 		$datarray["guid"] = $guid;
 		$datarray["uri"] = self::getUriFromGuid($author, $guid);
 
-		$datarray["verb"] = ACTIVITY_POST;
+		$datarray["verb"] = Activity::POST;
 		$datarray["gravity"] = GRAVITY_COMMENT;
 
 		if ($thr_uri != "") {
@@ -1854,7 +1855,7 @@ class Diaspora
 			$datarray["parent-uri"] = $parent_item["uri"];
 		}
 
-		$datarray["object-type"] = ACTIVITY_OBJ_COMMENT;
+		$datarray["object-type"] = Activity\ObjectType::COMMENT;
 
 		$datarray["protocol"] = Conversation::PARCEL_DIASPORA;
 		$datarray["source"] = $xml;
@@ -2062,9 +2063,9 @@ class Diaspora
 		// "positive" = "false" would be a Dislike - wich isn't currently supported by Diaspora
 		// We would accept this anyhow.
 		if ($positive == "true") {
-			$verb = ACTIVITY_LIKE;
+			$verb = Activity::LIKE;
 		} else {
-			$verb = ACTIVITY_DISLIKE;
+			$verb = Activity::DISLIKE;
 		}
 
 		$datarray = [];
@@ -2085,7 +2086,7 @@ class Diaspora
 		$datarray["gravity"] = GRAVITY_ACTIVITY;
 		$datarray["parent-uri"] = $parent_item["uri"];
 
-		$datarray["object-type"] = ACTIVITY_OBJ_NOTE;
+		$datarray["object-type"] = Activity\ObjectType::NOTE;
 
 		$datarray["body"] = $verb;
 
@@ -2684,9 +2685,9 @@ class Diaspora
 		$datarray['uri'] = self::getUriFromGuid($author, $datarray['guid']);
 		$datarray['parent-uri'] = $parent['uri'];
 
-		$datarray['verb'] = $datarray['body'] = ACTIVITY2_ANNOUNCE;
+		$datarray['verb'] = $datarray['body'] = Activity::ANNOUNCE;
 		$datarray['gravity'] = GRAVITY_ACTIVITY;
-		$datarray['object-type'] = ACTIVITY_OBJ_NOTE;
+		$datarray['object-type'] = Activity\ObjectType::NOTE;
 
 		$datarray['protocol'] = $item['protocol'];
 
@@ -2757,7 +2758,7 @@ class Diaspora
 		$datarray["guid"] = $guid;
 		$datarray["uri"] = $datarray["parent-uri"] = self::getUriFromGuid($author, $guid);
 
-		$datarray["verb"] = ACTIVITY_POST;
+		$datarray["verb"] = Activity::POST;
 		$datarray["gravity"] = GRAVITY_PARENT;
 
 		$datarray["protocol"] = Conversation::PARCEL_DIASPORA;
@@ -2962,9 +2963,9 @@ class Diaspora
 					XML::unescape($photo->remote_photo_name)."[/img]\n".$body;
 			}
 
-			$datarray["object-type"] = ACTIVITY_OBJ_IMAGE;
+			$datarray["object-type"] = Activity\ObjectType::IMAGE;
 		} else {
-			$datarray["object-type"] = ACTIVITY_OBJ_NOTE;
+			$datarray["object-type"] = Activity\ObjectType::NOTE;
 
 			// Add OEmbed and other information to the body
 			if (!self::isRedmatrix($contact["url"])) {
@@ -2994,7 +2995,7 @@ class Diaspora
 		$datarray["guid"] = $guid;
 		$datarray["uri"] = $datarray["parent-uri"] = self::getUriFromGuid($author, $guid);
 
-		$datarray["verb"] = ACTIVITY_POST;
+		$datarray["verb"] = Activity::POST;
 		$datarray["gravity"] = GRAVITY_PARENT;
 
 		$datarray["protocol"] = Conversation::PARCEL_DIASPORA;
@@ -3780,9 +3781,9 @@ class Diaspora
 
 		$target_type = ($parent["uri"] === $parent["parent-uri"] ? "Post" : "Comment");
 		$positive = null;
-		if ($item['verb'] === ACTIVITY_LIKE) {
+		if ($item['verb'] === Activity::LIKE) {
 			$positive = "true";
-		} elseif ($item['verb'] === ACTIVITY_DISLIKE) {
+		} elseif ($item['verb'] === Activity::DISLIKE) {
 			$positive = "false";
 		}
 
@@ -3811,13 +3812,13 @@ class Diaspora
 		}
 
 		switch ($item['verb']) {
-			case ACTIVITY_ATTEND:
+			case Activity::ATTEND:
 				$attend_answer = 'accepted';
 				break;
-			case ACTIVITY_ATTENDNO:
+			case Activity::ATTENDNO:
 				$attend_answer = 'declined';
 				break;
-			case ACTIVITY_ATTENDMAYBE:
+			case Activity::ATTENDMAYBE:
 				$attend_answer = 'tentative';
 				break;
 			default:
@@ -3913,13 +3914,13 @@ class Diaspora
 	 */
 	public static function sendFollowup(array $item, array $owner, array $contact, $public_batch = false)
 	{
-		if (in_array($item['verb'], [ACTIVITY_ATTEND, ACTIVITY_ATTENDNO, ACTIVITY_ATTENDMAYBE])) {
+		if (in_array($item['verb'], [Activity::ATTEND, Activity::ATTENDNO, Activity::ATTENDMAYBE])) {
 			$message = self::constructAttend($item, $owner);
 			$type = "event_participation";
-		} elseif (in_array($item["verb"], [ACTIVITY_LIKE, ACTIVITY_DISLIKE])) {
+		} elseif (in_array($item["verb"], [Activity::LIKE, Activity::DISLIKE])) {
 			$message = self::constructLike($item, $owner);
 			$type = "like";
-		} elseif (!in_array($item["verb"], [ACTIVITY_FOLLOW, ACTIVITY_TAG])) {
+		} elseif (!in_array($item["verb"], [Activity::FOLLOW, Activity::TAG])) {
 			$message = self::constructComment($item, $owner);
 			$type = "comment";
 		}
@@ -3948,7 +3949,7 @@ class Diaspora
 			$message = ["author" => $item['signer'],
 					"target_guid" => $signed_parts[0],
 					"target_type" => $signed_parts[1]];
-		} elseif (in_array($item["verb"], [ACTIVITY_LIKE, ACTIVITY_DISLIKE])) {
+		} elseif (in_array($item["verb"], [Activity::LIKE, Activity::DISLIKE])) {
 			$message = ["author" => $signed_parts[4],
 					"guid" => $signed_parts[1],
 					"parent_guid" => $signed_parts[3],
@@ -3993,7 +3994,7 @@ class Diaspora
 	{
 		if ($item["deleted"]) {
 			return self::sendRetraction($item, $owner, $contact, $public_batch, true);
-		} elseif (in_array($item["verb"], [ACTIVITY_LIKE, ACTIVITY_DISLIKE])) {
+		} elseif (in_array($item["verb"], [Activity::LIKE, Activity::DISLIKE])) {
 			$type = "like";
 		} else {
 			$type = "comment";
@@ -4054,7 +4055,7 @@ class Diaspora
 
 		if ($item['id'] == $item['parent']) {
 			$target_type = "Post";
-		} elseif (in_array($item["verb"], [ACTIVITY_LIKE, ACTIVITY_DISLIKE])) {
+		} elseif (in_array($item["verb"], [Activity::LIKE, Activity::DISLIKE])) {
 			$target_type = "Like";
 		} else {
 			$target_type = "Comment";
@@ -4320,7 +4321,7 @@ class Diaspora
 			return false;
 		}
 
-		if (!in_array($item["verb"], [ACTIVITY_LIKE, ACTIVITY_DISLIKE])) {
+		if (!in_array($item["verb"], [Activity::LIKE, Activity::DISLIKE])) {
 			return false;
 		}
 
diff --git a/src/Protocol/Feed.php b/src/Protocol/Feed.php
index c678cf0ae8..b7e7ce9201 100644
--- a/src/Protocol/Feed.php
+++ b/src/Protocol/Feed.php
@@ -14,6 +14,7 @@ use Friendica\Core\Protocol;
 use Friendica\Core\System;
 use Friendica\Database\DBA;
 use Friendica\Model\Item;
+use Friendica\Protocol\ActivityNamespace;
 use Friendica\Util\Network;
 use Friendica\Util\XML;
 
@@ -59,13 +60,13 @@ class Feed {
 		$doc = new DOMDocument();
 		@$doc->loadXML(trim($xml));
 		$xpath = new DOMXPath($doc);
-		$xpath->registerNamespace('atom', NAMESPACE_ATOM1);
+		$xpath->registerNamespace('atom', ActivityNamespace::ATOM1);
 		$xpath->registerNamespace('dc', "http://purl.org/dc/elements/1.1/");
 		$xpath->registerNamespace('content', "http://purl.org/rss/1.0/modules/content/");
 		$xpath->registerNamespace('rdf', "http://www.w3.org/1999/02/22-rdf-syntax-ns#");
 		$xpath->registerNamespace('rss', "http://purl.org/rss/1.0/");
 		$xpath->registerNamespace('media', "http://search.yahoo.com/mrss/");
-		$xpath->registerNamespace('poco', NAMESPACE_POCO);
+		$xpath->registerNamespace('poco', ActivityNamespace::POCO);
 
 		$author = [];
 		$entries = null;
@@ -198,8 +199,8 @@ class Feed {
 		$header["origin"] = 0;
 		$header["gravity"] = GRAVITY_PARENT;
 		$header["private"] = 2;
-		$header["verb"] = ACTIVITY_POST;
-		$header["object-type"] = ACTIVITY_OBJ_NOTE;
+		$header["verb"] = Activity::POST;
+		$header["object-type"] = Activity\ObjectType::NOTE;
 
 		$header["contact-id"] = $contact["id"];
 
@@ -420,7 +421,7 @@ class Feed {
 				$item["title"] = "";
 				$item["body"] = $item["body"].add_page_info($item["plink"], false, $preview, ($contact["fetch_further_information"] == 2), $contact["ffi_keyword_blacklist"]);
 				$item["tag"] = add_page_keywords($item["plink"], $preview, ($contact["fetch_further_information"] == 2), $contact["ffi_keyword_blacklist"]);
-				$item["object-type"] = ACTIVITY_OBJ_BOOKMARK;
+				$item["object-type"] = Activity\ObjectType::BOOKMARK;
 				unset($item["attach"]);
 			} else {
 				if (!empty($summary)) {
diff --git a/src/Protocol/OStatus.php b/src/Protocol/OStatus.php
index afd406f972..c88a740c0e 100644
--- a/src/Protocol/OStatus.php
+++ b/src/Protocol/OStatus.php
@@ -10,21 +10,22 @@ use Friendica\Content\Text\BBCode;
 use Friendica\Content\Text\HTML;
 use Friendica\Core\Cache;
 use Friendica\Core\Config;
-use Friendica\Core\PConfig;
 use Friendica\Core\L10n;
-use Friendica\Core\Logger;
 use Friendica\Core\Lock;
+use Friendica\Core\Logger;
+use Friendica\Core\PConfig;
 use Friendica\Core\Protocol;
 use Friendica\Core\System;
 use Friendica\Database\DBA;
+use Friendica\Model\APContact;
 use Friendica\Model\Contact;
 use Friendica\Model\Conversation;
 use Friendica\Model\GContact;
-use Friendica\Model\APContact;
 use Friendica\Model\Item;
 use Friendica\Model\User;
 use Friendica\Network\Probe;
 use Friendica\Object\Image;
+use Friendica\Protocol\ActivityNamespace;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Network;
 use Friendica\Util\Proxy as ProxyUtils;
@@ -261,14 +262,14 @@ class OStatus
 		@$doc->loadXML($xml);
 
 		$xpath = new DOMXPath($doc);
-		$xpath->registerNamespace('atom', NAMESPACE_ATOM1);
-		$xpath->registerNamespace('thr', NAMESPACE_THREAD);
-		$xpath->registerNamespace('georss', NAMESPACE_GEORSS);
-		$xpath->registerNamespace('activity', NAMESPACE_ACTIVITY);
-		$xpath->registerNamespace('media', NAMESPACE_MEDIA);
-		$xpath->registerNamespace('poco', NAMESPACE_POCO);
-		$xpath->registerNamespace('ostatus', NAMESPACE_OSTATUS);
-		$xpath->registerNamespace('statusnet', NAMESPACE_STATUSNET);
+		$xpath->registerNamespace('atom', ActivityNamespace::ATOM1);
+		$xpath->registerNamespace('thr', ActivityNamespace::THREAD);
+		$xpath->registerNamespace('georss', ActivityNamespace::GEORSS);
+		$xpath->registerNamespace('activity', ActivityNamespace::ACTIVITY);
+		$xpath->registerNamespace('media', ActivityNamespace::MEDIA);
+		$xpath->registerNamespace('poco', ActivityNamespace::POCO);
+		$xpath->registerNamespace('ostatus', ActivityNamespace::OSTATUS);
+		$xpath->registerNamespace('statusnet', ActivityNamespace::STATUSNET);
 
 		$contact = ["id" => 0];
 
@@ -342,14 +343,14 @@ class OStatus
 		@$doc->loadXML($xml);
 
 		$xpath = new DOMXPath($doc);
-		$xpath->registerNamespace('atom', NAMESPACE_ATOM1);
-		$xpath->registerNamespace('thr', NAMESPACE_THREAD);
-		$xpath->registerNamespace('georss', NAMESPACE_GEORSS);
-		$xpath->registerNamespace('activity', NAMESPACE_ACTIVITY);
-		$xpath->registerNamespace('media', NAMESPACE_MEDIA);
-		$xpath->registerNamespace('poco', NAMESPACE_POCO);
-		$xpath->registerNamespace('ostatus', NAMESPACE_OSTATUS);
-		$xpath->registerNamespace('statusnet', NAMESPACE_STATUSNET);
+		$xpath->registerNamespace('atom', ActivityNamespace::ATOM1);
+		$xpath->registerNamespace('thr', ActivityNamespace::THREAD);
+		$xpath->registerNamespace('georss', ActivityNamespace::GEORSS);
+		$xpath->registerNamespace('activity', ActivityNamespace::ACTIVITY);
+		$xpath->registerNamespace('media', ActivityNamespace::MEDIA);
+		$xpath->registerNamespace('poco', ActivityNamespace::POCO);
+		$xpath->registerNamespace('ostatus', ActivityNamespace::OSTATUS);
+		$xpath->registerNamespace('statusnet', ActivityNamespace::STATUSNET);
 
 		$hub = "";
 		$hub_items = $xpath->query("/atom:feed/atom:link[@rel='hub']")->item(0);
@@ -428,12 +429,12 @@ class OStatus
 			$item["verb"] = XML::getFirstNodeValue($xpath, 'activity:verb/text()', $entry);
 
 			// Delete a message
-			if (in_array($item["verb"], ['qvitter-delete-notice', ACTIVITY_DELETE, 'delete'])) {
+			if (in_array($item["verb"], ['qvitter-delete-notice', Activity::DELETE, 'delete'])) {
 				self::deleteNotice($item);
 				continue;
 			}
 
-			if (in_array($item["verb"], [NAMESPACE_OSTATUS."/unfavorite", ACTIVITY_UNFAVORITE])) {
+			if (in_array($item["verb"], [Activity::O_UNFAVOURITE, Activity::UNFAVORITE])) {
 				// Ignore "Unfavorite" message
 				Logger::log("Ignore unfavorite message ".print_r($item, true), Logger::DEBUG);
 				continue;
@@ -447,7 +448,7 @@ class OStatus
 				Logger::log('Processing post with URI '.$item["uri"].' for user '.$importer["uid"].'.', Logger::DEBUG);
 			}
 
-			if ($item["verb"] == ACTIVITY_JOIN) {
+			if ($item["verb"] == Activity::JOIN) {
 				// ignore "Join" messages
 				Logger::log("Ignore join message ".print_r($item, true), Logger::DEBUG);
 				continue;
@@ -459,29 +460,29 @@ class OStatus
 				continue;
 			}
 
-			if ($item["verb"] == ACTIVITY_FOLLOW) {
+			if ($item["verb"] == Activity::FOLLOW) {
 				Contact::addRelationship($importer, $contact, $item);
 				continue;
 			}
 
-			if ($item["verb"] == NAMESPACE_OSTATUS."/unfollow") {
+			if ($item["verb"] == Activity::O_UNFOLLOW) {
 				$dummy = null;
 				Contact::removeFollower($importer, $contact, $item, $dummy);
 				continue;
 			}
 
-			if ($item["verb"] == ACTIVITY_FAVORITE) {
+			if ($item["verb"] == Activity::FAVORITE) {
 				$orig_uri = $xpath->query("activity:object/atom:id", $entry)->item(0)->nodeValue;
 				Logger::log("Favorite ".$orig_uri." ".print_r($item, true));
 
-				$item["verb"] = ACTIVITY_LIKE;
+				$item["verb"] = Activity::LIKE;
 				$item["parent-uri"] = $orig_uri;
 				$item["gravity"] = GRAVITY_ACTIVITY;
-				$item["object-type"] = ACTIVITY_OBJ_NOTE;
+				$item["object-type"] = Activity\ObjectType::NOTE;
 			}
 
 			// http://activitystrea.ms/schema/1.0/rsvp-yes
-			if (!in_array($item["verb"], [ACTIVITY_POST, ACTIVITY_LIKE, ACTIVITY_SHARE])) {
+			if (!in_array($item["verb"], [Activity::POST, Activity::LIKE, Activity::SHARE])) {
 				Logger::log("Unhandled verb ".$item["verb"]." ".print_r($item, true), Logger::DEBUG);
 			}
 
@@ -504,7 +505,7 @@ class OStatus
 					if ($valid) {
 						// Never post a thread when the only interaction by our contact was a like
 						$valid = false;
-						$verbs = [ACTIVITY_POST, ACTIVITY_SHARE];
+						$verbs = [Activity::POST, Activity::SHARE];
 						foreach (self::$itemlist as $item) {
 							if (in_array($item['verb'], $verbs) && Contact::isSharingByURL($item['author-link'], $item['uid'])) {
 								$valid = true;
@@ -592,10 +593,10 @@ class OStatus
 	{
 		$item["body"] = HTML::toBBCode(XML::getFirstNodeValue($xpath, 'atom:content/text()', $entry));
 		$item["object-type"] = XML::getFirstNodeValue($xpath, 'activity:object-type/text()', $entry);
-		if (($item["object-type"] == ACTIVITY_OBJ_BOOKMARK) || ($item["object-type"] == ACTIVITY_OBJ_EVENT)) {
+		if (($item["object-type"] == Activity\ObjectType::BOOKMARK) || ($item["object-type"] == Activity\ObjectType::EVENT)) {
 			$item["title"] = XML::getFirstNodeValue($xpath, 'atom:title/text()', $entry);
 			$item["body"] = XML::getFirstNodeValue($xpath, 'atom:summary/text()', $entry);
-		} elseif ($item["object-type"] == ACTIVITY_OBJ_QUESTION) {
+		} elseif ($item["object-type"] == Activity\ObjectType::QUESTION) {
 			$item["title"] = XML::getFirstNodeValue($xpath, 'atom:title/text()', $entry);
 		}
 
@@ -676,7 +677,7 @@ class OStatus
 			}
 		}
 		// Is it a repeated post?
-		if (($repeat_of != "") || ($item["verb"] == ACTIVITY_SHARE)) {
+		if (($repeat_of != "") || ($item["verb"] == Activity::SHARE)) {
 			$link_data = self::processRepeatedItem($xpath, $entry, $item, $importer);
 			if (!empty($link_data['add_body'])) {
 				$add_body .= $link_data['add_body'];
@@ -691,7 +692,7 @@ class OStatus
 		}
 
 		// Mastodon Content Warning
-		if (($item["verb"] == ACTIVITY_POST) && $xpath->evaluate('boolean(atom:summary)', $entry)) {
+		if (($item["verb"] == Activity::POST) && $xpath->evaluate('boolean(atom:summary)', $entry)) {
 			$clear_text = XML::getFirstNodeValue($xpath, 'atom:summary/text()', $entry);
 			if (!empty($clear_text)) {
 				$item['content-warning'] = HTML::toBBCode($clear_text);
@@ -803,9 +804,9 @@ class OStatus
 		@$doc->loadXML($xml);
 
 		$xpath = new DOMXPath($doc);
-		$xpath->registerNamespace('atom', NAMESPACE_ATOM1);
-		$xpath->registerNamespace('thr', NAMESPACE_THREAD);
-		$xpath->registerNamespace('ostatus', NAMESPACE_OSTATUS);
+		$xpath->registerNamespace('atom', ActivityNamespace::ATOM1);
+		$xpath->registerNamespace('thr', ActivityNamespace::THREAD);
+		$xpath->registerNamespace('ostatus', ActivityNamespace::OSTATUS);
 
 		$entries = $xpath->query('/atom:feed/atom:entry');
 
@@ -1067,7 +1068,7 @@ class OStatus
 		$item["object-type"] = XML::getFirstNodeValue($xpath, 'activity:object-type/text()', $activityobject);
 
 		// Mastodon Content Warning
-		if (($item["verb"] == ACTIVITY_POST) && $xpath->evaluate('boolean(atom:summary)', $activityobject)) {
+		if (($item["verb"] == Activity::POST) && $xpath->evaluate('boolean(atom:summary)', $activityobject)) {
 			$clear_text = XML::getFirstNodeValue($xpath, 'atom:summary/text()', $activityobject);
 			if (!empty($clear_text)) {
 				$item['content-warning'] = HTML::toBBCode($clear_text);
@@ -1105,8 +1106,8 @@ class OStatus
 				switch ($attribute['rel']) {
 					case "alternate":
 						$item["plink"] = $attribute['href'];
-						if (($item["object-type"] == ACTIVITY_OBJ_QUESTION)
-							|| ($item["object-type"] == ACTIVITY_OBJ_EVENT)
+						if (($item["object-type"] == Activity\ObjectType::QUESTION)
+							|| ($item["object-type"] == Activity\ObjectType::EVENT)
 						) {
 							$item["body"] .= add_page_info($attribute['href']);
 						}
@@ -1135,7 +1136,7 @@ class OStatus
 						}
 						break;
 					case "related":
-						if ($item["object-type"] != ACTIVITY_OBJ_BOOKMARK) {
+						if ($item["object-type"] != Activity\ObjectType::BOOKMARK) {
 							if (!isset($item["parent-uri"])) {
 								$item["parent-uri"] = $attribute['href'];
 							}
@@ -1281,17 +1282,17 @@ class OStatus
 	 */
 	private static function addHeader(DOMDocument $doc, array $owner, $filter, $feed_mode = false)
 	{
-		$root = $doc->createElementNS(NAMESPACE_ATOM1, 'feed');
+		$root = $doc->createElementNS(ActivityNamespace::ATOM1, 'feed');
 		$doc->appendChild($root);
 
-		$root->setAttribute("xmlns:thr", NAMESPACE_THREAD);
-		$root->setAttribute("xmlns:georss", NAMESPACE_GEORSS);
-		$root->setAttribute("xmlns:activity", NAMESPACE_ACTIVITY);
-		$root->setAttribute("xmlns:media", NAMESPACE_MEDIA);
-		$root->setAttribute("xmlns:poco", NAMESPACE_POCO);
-		$root->setAttribute("xmlns:ostatus", NAMESPACE_OSTATUS);
-		$root->setAttribute("xmlns:statusnet", NAMESPACE_STATUSNET);
-		$root->setAttribute("xmlns:mastodon", NAMESPACE_MASTODON);
+		$root->setAttribute("xmlns:thr", ActivityNamespace::THREAD);
+		$root->setAttribute("xmlns:georss", ActivityNamespace::GEORSS);
+		$root->setAttribute("xmlns:activity", ActivityNamespace::ACTIVITY);
+		$root->setAttribute("xmlns:media", ActivityNamespace::MEDIA);
+		$root->setAttribute("xmlns:poco", ActivityNamespace::POCO);
+		$root->setAttribute("xmlns:ostatus", ActivityNamespace::OSTATUS);
+		$root->setAttribute("xmlns:statusnet", ActivityNamespace::STATUSNET);
+		$root->setAttribute("xmlns:mastodon", ActivityNamespace::MASTODON);
 
 		$title = '';
 		$selfUri = '/feed/' . $owner["nick"] . '/';
@@ -1461,9 +1462,9 @@ class OStatus
 		$author = $doc->createElement("author");
 		XML::addElement($doc, $author, "id", $owner["url"]);
 		if ($owner['account-type'] == User::ACCOUNT_TYPE_COMMUNITY) {
-			XML::addElement($doc, $author, "activity:object-type", ACTIVITY_OBJ_GROUP);
+			XML::addElement($doc, $author, "activity:object-type", Activity\ObjectType::GROUP);
 		} else {
-			XML::addElement($doc, $author, "activity:object-type", ACTIVITY_OBJ_PERSON);
+			XML::addElement($doc, $author, "activity:object-type", Activity\ObjectType::PERSON);
 		}
 		XML::addElement($doc, $author, "uri", $owner["url"]);
 		XML::addElement($doc, $author, "name", $owner["nick"]);
@@ -1544,7 +1545,7 @@ class OStatus
 			return $item['verb'];
 		}
 
-		return ACTIVITY_POST;
+		return Activity::POST;
 	}
 
 	/**
@@ -1556,11 +1557,11 @@ class OStatus
 	 */
 	private static function constructObjecttype(array $item)
 	{
-		if (!empty($item['object-type']) && in_array($item['object-type'], [ACTIVITY_OBJ_NOTE, ACTIVITY_OBJ_COMMENT])) {
+		if (!empty($item['object-type']) && in_array($item['object-type'], [Activity\ObjectType::NOTE, Activity\ObjectType::COMMENT])) {
 			return $item['object-type'];
 		}
 
-		return ACTIVITY_OBJ_NOTE;
+		return Activity\ObjectType::NOTE;
 	}
 
 	/**
@@ -1589,9 +1590,9 @@ class OStatus
 			return $xml;
 		}
 
-		if ($item["verb"] == ACTIVITY_LIKE) {
+		if ($item["verb"] == Activity::LIKE) {
 			return self::likeEntry($doc, $item, $owner, $toplevel);
-		} elseif (in_array($item["verb"], [ACTIVITY_FOLLOW, NAMESPACE_OSTATUS."/unfollow"])) {
+		} elseif (in_array($item["verb"], [Activity::FOLLOW, Activity::O_UNFOLLOW])) {
 			return self::followEntry($doc, $item, $owner, $toplevel);
 		} else {
 			return self::noteEntry($doc, $item, $owner, $toplevel, $feed_mode);
@@ -1705,11 +1706,11 @@ class OStatus
 
 		$title = $owner["nick"]." repeated a notice by ".$contact["nick"];
 
-		self::entryContent($doc, $entry, $item, $owner, $title, ACTIVITY_SHARE, false);
+		self::entryContent($doc, $entry, $item, $owner, $title, Activity::SHARE, false);
 
 		$as_object = $doc->createElement("activity:object");
 
-		XML::addElement($doc, $as_object, "activity:object-type", NAMESPACE_ACTIVITY_SCHEMA."activity");
+		XML::addElement($doc, $as_object, "activity:object-type", ActivityNamespace::ACTIVITY_SCHEMA . "activity");
 
 		self::entryContent($doc, $as_object, $repeated_item, $owner, "", "", false);
 
@@ -1759,7 +1760,7 @@ class OStatus
 
 		$entry = self::entryHeader($doc, $owner, $item, $toplevel);
 
-		$verb = NAMESPACE_ACTIVITY_SCHEMA."favorite";
+		$verb = ActivityNamespace::ACTIVITY_SCHEMA . "favorite";
 		self::entryContent($doc, $entry, $item, $owner, "Favorite", $verb, false);
 
 		$parent = Item::selectFirst([], ['uri' => $item["thr-parent"], 'uid' => $item["uid"]]);
@@ -1790,7 +1791,7 @@ class OStatus
 	private static function addPersonObject(DOMDocument $doc, array $owner, array $contact)
 	{
 		$object = $doc->createElement("activity:object");
-		XML::addElement($doc, $object, "activity:object-type", ACTIVITY_OBJ_PERSON);
+		XML::addElement($doc, $object, "activity:object-type", Activity\ObjectType::PERSON);
 
 		if ($contact['network'] == Protocol::PHANTOM) {
 			XML::addElement($doc, $object, "id", $contact['url']);
@@ -1858,7 +1859,7 @@ class OStatus
 			$connect_id = 0;
 		}
 
-		if ($item['verb'] == ACTIVITY_FOLLOW) {
+		if ($item['verb'] == Activity::FOLLOW) {
 			$message = L10n::t('%s is now following %s.');
 			$title = L10n::t('following');
 			$action = "subscription";
@@ -1918,7 +1919,7 @@ class OStatus
 
 		$entry = self::entryHeader($doc, $owner, $item, $toplevel);
 
-		XML::addElement($doc, $entry, "activity:object-type", ACTIVITY_OBJ_NOTE);
+		XML::addElement($doc, $entry, "activity:object-type", Activity\ObjectType::NOTE);
 
 		self::entryContent($doc, $entry, $item, $owner, $title, '', true, $feed_mode);
 
@@ -1950,16 +1951,16 @@ class OStatus
 				$entry->appendChild($author);
 			}
 		} else {
-			$entry = $doc->createElementNS(NAMESPACE_ATOM1, "entry");
+			$entry = $doc->createElementNS(ActivityNamespace::ATOM1, "entry");
 
-			$entry->setAttribute("xmlns:thr", NAMESPACE_THREAD);
-			$entry->setAttribute("xmlns:georss", NAMESPACE_GEORSS);
-			$entry->setAttribute("xmlns:activity", NAMESPACE_ACTIVITY);
-			$entry->setAttribute("xmlns:media", NAMESPACE_MEDIA);
-			$entry->setAttribute("xmlns:poco", NAMESPACE_POCO);
-			$entry->setAttribute("xmlns:ostatus", NAMESPACE_OSTATUS);
-			$entry->setAttribute("xmlns:statusnet", NAMESPACE_STATUSNET);
-			$entry->setAttribute("xmlns:mastodon", NAMESPACE_MASTODON);
+			$entry->setAttribute("xmlns:thr", ActivityNamespace::THREAD);
+			$entry->setAttribute("xmlns:georss", ActivityNamespace::GEORSS);
+			$entry->setAttribute("xmlns:activity", ActivityNamespace::ACTIVITY);
+			$entry->setAttribute("xmlns:media", ActivityNamespace::MEDIA);
+			$entry->setAttribute("xmlns:poco", ActivityNamespace::POCO);
+			$entry->setAttribute("xmlns:ostatus", ActivityNamespace::OSTATUS);
+			$entry->setAttribute("xmlns:statusnet", ActivityNamespace::STATUSNET);
+			$entry->setAttribute("xmlns:mastodon", ActivityNamespace::MASTODON);
 
 			$author = self::addAuthor($doc, $owner);
 			$entry->appendChild($author);
@@ -2111,14 +2112,14 @@ class OStatus
 				XML::addElement($doc, $entry, "link", "",
 					[
 						"rel" => "mentioned",
-						"ostatus:object-type" => ACTIVITY_OBJ_GROUP,
+						"ostatus:object-type" => Activity\ObjectType::GROUP,
 						"href" => $mention]
 				);
 			} else {
 				XML::addElement($doc, $entry, "link", "",
 					[
 						"rel" => "mentioned",
-						"ostatus:object-type" => ACTIVITY_OBJ_PERSON,
+						"ostatus:object-type" => Activity\ObjectType::PERSON,
 						"href" => $mention]
 				);
 			}
@@ -2231,7 +2232,7 @@ class OStatus
 
 		if ($filter === 'comments') {
 			$condition[0] .= " AND `object-type` = ? ";
-			$condition[] = ACTIVITY_OBJ_COMMENT;
+			$condition[] = Activity\ObjectType::COMMENT;
 		}
 
 		if ($owner['account-type'] != User::ACCOUNT_TYPE_COMMUNITY) {
diff --git a/src/Worker/OnePoll.php b/src/Worker/OnePoll.php
index d9bdd66fbd..3f8b98ead1 100644
--- a/src/Worker/OnePoll.php
+++ b/src/Worker/OnePoll.php
@@ -14,6 +14,7 @@ use Friendica\Database\DBA;
 use Friendica\Model\Contact;
 use Friendica\Model\Item;
 use Friendica\Model\User;
+use Friendica\Protocol\Activity;
 use Friendica\Protocol\ActivityPub;
 use Friendica\Protocol\Email;
 use Friendica\Protocol\PortableContact;
@@ -493,8 +494,8 @@ class OnePoll
 					Logger::log("Mail: Parsing mail ".$msg_uid, Logger::DATA);
 
 					$datarray = [];
-					$datarray['verb'] = ACTIVITY_POST;
-					$datarray['object-type'] = ACTIVITY_OBJ_NOTE;
+					$datarray['verb'] = Activity::POST;
+					$datarray['object-type'] = Activity\ObjectType::NOTE;
 					$datarray['network'] = Protocol::MAIL;
 					// $meta = Email::messageMeta($mbox, $msg_uid);
 
diff --git a/tests/src/Protocol/ActivityTest.php b/tests/src/Protocol/ActivityTest.php
index b6fcbf3954..a3e9c11487 100644
--- a/tests/src/Protocol/ActivityTest.php
+++ b/tests/src/Protocol/ActivityTest.php
@@ -3,6 +3,7 @@
 namespace Friendica\Test\Protocol;
 
 use Friendica\Protocol\Activity;
+use Friendica\Protocol\ActivityNamespace;
 use Friendica\Test\MockedTest;
 
 class ActivityTest extends MockedTest
@@ -16,13 +17,13 @@ class ActivityTest extends MockedTest
 				'assert' => true,
 			],
 			'simple' => [
-				'haystack' => ACTIVITY_OBJ_TAGTERM,
-				'needle' => ACTIVITY_OBJ_TAGTERM,
+				'haystack' => Activity\ObjectType::TAGTERM,
+				'needle' => Activity\ObjectType::TAGTERM,
 				'assert' => true,
 			],
 			'withNamespace' => [
 				'haystack' => 'tagterm',
-				'needle' => NAMESPACE_ACTIVITY_SCHEMA . ACTIVITY_OBJ_TAGTERM,
+				'needle' => ActivityNamespace::ACTIVITY_SCHEMA . Activity\ObjectType::TAGTERM,
 				'assert' => true,
 			],
 			'invalidSimple' => [
@@ -32,12 +33,12 @@ class ActivityTest extends MockedTest
 			],
 			'invalidWithOutNamespace' => [
 				'haystack' => 'tagterm',
-				'needle' => ACTIVITY_OBJ_TAGTERM,
+				'needle' => Activity\ObjectType::TAGTERM,
 				'assert' => false,
 			],
 			'withSubPath' => [
 				'haystack' => 'tagterm',
-				'needle' =>  NAMESPACE_ACTIVITY_SCHEMA . '/bla/' . ACTIVITY_OBJ_TAGTERM,
+				'needle' => ActivityNamespace::ACTIVITY_SCHEMA . '/bla/' . Activity\ObjectType::TAGTERM,
 				'assert' => true,
 			],
 		];
@@ -54,4 +55,12 @@ class ActivityTest extends MockedTest
 
 		$this->assertEquals($assert, $activity->match($haystack, $needle));
 	}
+
+	public function testIsHidden()
+	{
+		$activity = new Activity();
+
+		$this->assertTrue($activity->isHidden(Activity::LIKE));
+		$this->assertFalse($activity->isHidden(Activity\ObjectType::BOOKMARK));
+	}
 }