diff --git a/lib/public/comments/icomment.php b/lib/public/comments/icomment.php
new file mode 100644
index 0000000000000000000000000000000000000000..c8f407624a01f9f25dc49a6bbd541004b382934a
--- /dev/null
+++ b/lib/public/comments/icomment.php
@@ -0,0 +1,199 @@
+<?php
+
+namespace OCP\Comments;
+
+/**
+ * Interface IComment
+ *
+ * This class represents a comment and offers methods for modification.
+ *
+ * @package OCP\Comments
+ * @since 9.0.0
+ */
+interface IComment {
+
+ /**
+ * returns the ID of the comment
+ *
+ * It may return an empty string, if the comment was not stored.
+ * It is expected that the concrete Comment implementation gives an ID
+ * by itself (e.g. after saving).
+ *
+ * @return string
+ * @since 9.0.0
+ */
+ public function getId();
+
+ /**
+ * sets the ID of the comment and returns itself
+ *
+ * It is only allowed to set the ID only, if the current id is an empty
+ * string (which means it is not stored in a database, storage or whatever
+ * the concrete implementation does), or vice versa. Changing a given ID is
+ * not permitted and must result in an IllegalIDChangeException.
+ *
+ * @param string $id
+ * @return IComment
+ * @throws IllegalIDChangeException
+ * @since 9.0.0
+ */
+ public function setId($id);
+
+ /**
+ * returns the parent ID of the comment
+ *
+ * @return string
+ * @since 9.0.0
+ */
+ public function getParentId();
+
+ /**
+ * sets the parent ID and returns itself
+ *
+ * @param string $parentId
+ * @return IComment
+ * @since 9.0.0
+ */
+ public function setParentId($parentId);
+
+ /**
+ * returns the number of children
+ *
+ * @return int
+ * @since 9.0.0
+ */
+ public function getChildrenCount();
+
+ /**
+ * sets the number of children
+ *
+ * @param int $count
+ * @return IComment
+ * @since 9.0.0
+ */
+ public function setChildrenCount($count);
+
+ /**
+ * returns the message of the comment
+ *
+ * @return string
+ * @since 9.0.0
+ */
+ public function getMessage();
+
+ /**
+ * sets the message of the comment and returns itself
+ *
+ * @param string $message
+ * @return IComment
+ * @since 9.0.0
+ */
+ public function setMessage($message);
+
+ /**
+ * returns the verb of the comment
+ *
+ * @return string
+ * @since 9.0.0
+ */
+ public function getVerb();
+
+ /**
+ * sets the verb of the comment, e.g. 'comment' or 'like'
+ *
+ * @param string $verb
+ * @return IComment
+ * @since 9.0.0
+ */
+ public function setVerb($verb);
+
+ /**
+ * returns the actor type
+ *
+ * @return string
+ * @since 9.0.0
+ */
+ public function getActorType();
+
+ /**
+ * returns the actor ID
+ *
+ * @return string
+ * @since 9.0.0
+ */
+ public function getActorId();
+
+ /**
+ * sets (overwrites) the actor type and id
+ *
+ * @param string $actorType e.g. 'user'
+ * @param string $actorId e.g. 'zombie234'
+ * @return IComment
+ * @since 9.0.0
+ */
+ public function setActor($actorType, $actorId);
+
+ /**
+ * returns the creation date of the comment.
+ *
+ * If not explicitly set, it shall default to the time of initialization.
+ *
+ * @return \DateTime
+ * @since 9.0.0
+ */
+ public function getCreationDateTime();
+
+ /**
+ * sets the creation date of the comment and returns itself
+ *
+ * @param \DateTime $dateTime
+ * @return IComment
+ * @since 9.0.0
+ */
+ public function setCreationDateTime(\DateTime $dateTime);
+
+ /**
+ * returns the date of the most recent child
+ *
+ * @return \DateTime
+ * @since 9.0.0
+ */
+ public function getLatestChildDateTime();
+
+ /**
+ * sets the date of the most recent child
+ *
+ * @param \DateTime $dateTime
+ * @return IComment
+ * @since 9.0.0
+ */
+ public function setLatestChildDateTime(\DateTime $dateTime);
+
+ /**
+ * returns the object type the comment is attached to
+ *
+ * @return string
+ * @since 9.0.0
+ */
+ public function getObjectType();
+
+ /**
+ * returns the object id the comment is attached to
+ *
+ * @return string
+ * @since 9.0.0
+ */
+ public function getObjectId();
+
+ /**
+ * sets (overwrites) the object of the comment
+ *
+ * @param string $objectType e.g. 'file'
+ * @param string $objectId e.g. '16435'
+ * @return IComment
+ * @since 9.0.0
+ */
+ public function setObject($objectType, $objectId);
+
+}
+
diff --git a/lib/public/comments/icommentsmanager.php b/lib/public/comments/icommentsmanager.php
new file mode 100644
index 0000000000000000000000000000000000000000..ebf7a34bf27a67898cf47775103e3bf498851b7b
--- /dev/null
+++ b/lib/public/comments/icommentsmanager.php
@@ -0,0 +1,161 @@
+<?php
+
+namespace OCP\Comments;
+
+/**
+ * Interface ICommentsManager
+ *
+ * This class manages the access to comments
+ *
+ * @package OCP\Comments
+ * @since 9.0.0
+ */
+interface ICommentsManager {
+
+ /**
+ * returns a comment instance
+ *
+ * @param string $id the ID of the comment
+ * @return IComment
+ * @throws NotFoundException
+ * @since 9.0.0
+ */
+ public function get($id);
+
+ /**
+ * returns the comment specified by the id and all it's child comments
+ *
+ * @param string $id
+ * @param int $limit max number of entries to return, 0 returns all
+ * @param int $offset the start entry
+ * @return []
+ * @since 9.0.0
+ *
+ * The return array looks like this
+ * [
+ * 'comment' => IComment, // root comment
+ * 'replies' =>
+ * [
+ * 0 =>
+ * [
+ * 'comment' => IComment,
+ * 'replies' =>
+ * [
+ * 0 =>
+ * [
+ * 'comment' => IComment,
+ * 'replies' => [ … ]
+ * ],
+ * …
+ * ]
+ * ]
+ * 1 =>
+ * [
+ * 'comment' => IComment,
+ * 'replies'=> [ … ]
+ * ],
+ * …
+ * ]
+ * ]
+ */
+ public function getTree($id, $limit = 0, $offset = 0);
+
+ /**
+ * returns comments for a specific object (e.g. a file).
+ *
+ * The sort order is always newest to oldest.
+ *
+ * @param string $objectType the object type, e.g. 'files'
+ * @param string $objectId the id of the object
+ * @param int $limit optional, number of maximum comments to be returned. if
+ * not specified, all comments are returned.
+ * @param int $offset optional, starting point
+ * @param \DateTime $notOlderThan optional, timestamp of the oldest comments
+ * that may be returned
+ * @return IComment[]
+ * @throws NotFoundException in case the requested type or id is not present
+ * @since 9.0.0
+ */
+ public function getForObject(
+ $objectType,
+ $objectId,
+ $limit = 0,
+ $offset = 0,
+ \DateTime $notOlderThan = null
+ );
+
+ /**
+ * @param $objectType string the object type, e.g. 'files'
+ * @param $objectId string the id of the object
+ * @return Int
+ * @throws NotFoundException in case the requested type or id is not present
+ * @since 9.0.0
+ */
+ public function getNumberOfCommentsForObject($objectType, $objectId);
+
+ /**
+ * creates a new comment and returns it. At this point of time, it is not
+ * saved in the used data storage. Use save() after setting other fields
+ * of the comment (e.g. message or verb).
+ *
+ * @param string $actorType the actor type (e.g. 'user')
+ * @param string $actorId a user id
+ * @param string $objectType the object type the comment is attached to
+ * @param string $objectId the object id the comment is attached to
+ * @return IComment
+ * @since 9.0.0
+ */
+ public function create($actorType, $actorId, $objectType, $objectId);
+
+ /**
+ * permanently deletes the comment specified by the ID
+ *
+ * When the comment has child comments, their parent ID will be changed to
+ * the parent ID of the item that is to be deleted.
+ *
+ * @param string $id
+ * @return bool
+ * @since 9.0.0
+ */
+ public function delete($id);
+
+ /**
+ * saves the comment permanently and returns it
+ *
+ * if the supplied comment has an empty ID, a new entry comment will be
+ * saved and the instance updated with the new ID.
+ *
+ * Otherwise, an existing comment will be updated.
+ *
+ * Throws NotFoundException when a comment that is to be updated does not
+ * exist anymore at this point of time.
+ *
+ * @param IComment
+ * @return bool
+ * @throws NotFoundException
+ * @since 9.0.0
+ */
+ public function save(&$comment);
+
+ /**
+ * removes references to specific actor (e.g. on user delete) of a comment.
+ * The comment itself must not get lost/deleted.
+ *
+ * @param string $actorType the actor type (e.g. 'user')
+ * @param string $actorId a user id
+ * @return boolean
+ * @since 9.0.0
+ */
+ public function deleteReferencesOfActor($actorType, $actorId);
+
+ /**
+ * deletes all comments made of a specific object (e.g. on file delete)
+ *
+ * @param string $objectType the object type (e.g. 'file')
+ * @param string $objectId e.g. the file id
+ * @return boolean
+ * @since 9.0.0
+ */
+ public function deleteCommentsAtObject($objectType, $objectId);
+
+}
diff --git a/lib/public/comments/illegalidchangeexception.php b/lib/public/comments/illegalidchangeexception.php
new file mode 100644
index 0000000000000000000000000000000000000000..4e13ef6e444098b1bcb551a90be9a6f642b95f2f
--- /dev/null
+++ b/lib/public/comments/illegalidchangeexception.php
@@ -0,0 +1,9 @@
+<?php
+
+namespace OCP\Comments;
+
+/**
+ * Exception for illegal attempts to modify a comment ID
+ * @since 9.0.0
+ */
+class IllegalIDChangeException extends \Exception {}
diff --git a/lib/public/comments/notfoundexception.php b/lib/public/comments/notfoundexception.php
new file mode 100644
index 0000000000000000000000000000000000000000..a82e703b79e7aac5ea1972b7d70a5291bf9f8e7b
--- /dev/null
+++ b/lib/public/comments/notfoundexception.php
@@ -0,0 +1,9 @@
+<?php
+
+namespace OCP\Comments;
+
+/**
+ * Exception for not found entity
+ * @since 9.0.0
+ */
+class NotFoundException extends \Exception {}