Appendix A. UML Metamodel
UML Definition Documents
The uml is defined by a set of documents published by the Object Management Group [UML-04]. These documents may be found on the OMG website (www.omg.org). They may be updated from time to time by the OMG. This appendix explains the structure of the UML semantic model described in the documents.
The UML is formally defined using a metamodel—that is, a model of the constructs in UML. The metamodel itself is expressed in UML. This is an example of a metacircular interpreter—that is, a language defined in terms of itself. Things are not completely circular. Only a small subset of UML is used to define the metamodel. ...