@InProceedings{Richters:1998:ER,
  author =       "Mark Richters and Martin Gogolla",
  title =        "On Formalizing the {UML} {Object Constraint Language}
                  {OCL}",
  booktitle =    "Proc. 17th Int. Conf. Conceptual Modeling (ER'98)",
  year =         "1998",
  editor =       "Tok Wang Ling and Sudha Ram and Mong Li Lee",
  volume =       "1507",
  series =       "LNCS",
  pages =        "449--464",
  publisher =    "Springer",
  isbn =         "3-540-65189-6",
  abstract =     "We present a formal semantics for the Object Constraint
                  Language (OCL) which is part of the Unified Modeling
                  Language (UML) -- an emerging standard language and
                  notation for object-oriented analysis and design.  In
                  context of information systems modeling, UML class
                  diagrams can be utilized for describing the overall
                  structure, whereas additional integrity constraints and
                  queries are specified with OCL expressions. By using OCL,
                  constraints and queries can be specified in a formal yet
                  comprehensible way. However, the OCL itself is currently
                  defined only in an informal way. Thus the semantics of
                  constraints is in general not precisely defined. Our
                  approach gives precise meaning to OCL concepts and to
                  some central aspects of UML class models. In consequence,
                  a formal semantics facilitates verification, validation
                  and simulation of models improving the quality of models
                  and software design.",
}