@InProceedings{Giese+1999g,
  AUTHOR = {Giese, Holger and Graf, Jörg and Wirtz, Guido},
  TITLE = {{Closing the Gap Between Object-Oriented Modeling of Structure
  and Behavior}},
  YEAR = {1999},
  MONTH = {October},
  BOOKTITLE = {UML'99 - The Second International Conference on The
  Unified Modeling Language Fort Collins, Colorado, USA},
  VOLUME = {1723},
  PAGES = {534-549},
  EDITOR = {France, Robert and Rumpe, Bernhard},
  SERIES = {Lecture Notes in Computer Science (LNCS)},
  PUBLISHER = {Springer Verlag},
  PS = {uml99.ps.gz},
  ABSTRACT = {The UML as standardized language for visual object-oriented
  modeling allows to capture the requirements as well as the structure
  and behavior of complex software systems. With the increasing demands
  of todays systems, behavior aspects like concurrency, distribution and
  reactivity become more important. But the language concepts of the UML
  for describing behavioral aspects are weak compared to its concepts
  for describing structures. Besides a lack of visual expressiveness, a
  deeper integration with the structure specification is missing. In order
  to close this gap, an expressive language for modeling object-oriented
  behavior is proposed with the OCoN approach. It describes contracts,
  object scheduling as well as control and data flow of services
  in a Petri-net-like form. A seamless visual embedding of contract
  specifications into service and object scheduling specifications is
  provided by different net types.}
}