Content of reference variables. Points to a data object (data reference) or an instance of a class (object reference). References in reference variables are either heap references or stack references. Internally, strings, internal tables, and boxed components are also addressed using references. From a technical point of view, an object in ABAP is referenced in more than one step. A reference is the address of an internal header (object header, string header, or table header), which contains the address of the actual object and other administrative information such as the data type of a referenced data object.