The task of modelling an Asset is more than just describing a single simple Asset. It is modelling the relationships between the Assets. In OPC UA, relationships can be modelled as References, where a Reference provides semantic information about the relationship. OPC UA has defined a number of References in OPC 10000-23 that can be used for modelling Assets. This list is extended by this document. The following ReferenceTypes will be illustrated in various examples in this annex:

Additional References may be defined or used to show additional relationships.