Almost all entities in the CDM are subclasses of VersionableEntity. This means that the changing (persistent) state of an entity through time can be recorded in the database, and recovered. This is quite a complex idea and is covered in full in the chapter on versioning. Versionable entities have two additional properties: updated, that holds the date-time when the object was last made persistent, and updatedBy, that provides the user that last updated the entity. Both work in an identical way to created and createdBy.