  In this document, we introduce a system model as a semantic domain for the
Unified Modeling Language (UML) [OMG07a, OMG07b]. The system model is supposed
to form a possible core and foundation of the UML semantics definition. For
that purpose, the definitions in this document are targeted towards UML which
means that central concepts of UML have been formalized as theories of the
system model. This document is structured as follows: In the rest of Chapter 1,
we discuss the general approach and highlight the main decisions. This chapter
is important to understand the rest of this document. Chapter 2 contains the
definition of the structural part of the system model. Chapters 3 and 4 contain
the control and communication related definition definitions which form the
basis to describe the state of a system in Chapter 5. Two variants of state
transitions systems are introduced to define object behavior in Chapters 6
(event-based) and 7 (timed). Chapter 8 concludes the document. This document is
the second version of the system model which is the result of a major effort to
define the structure, behavior and interaction of object oriented, possibly
distributed systems abstract enough to be of general value, but also in
sufficient detail for a semantic foundation of the UML. The first version of
the system model can be found in [BCR06, BCR07a, BCR07b].
