UML for Modeling Complex Real-Time Systems

The embedded real-time software systems encountered in applications such
as telecommunications, aerospace, and defense typically tend to be large and
extremely complex. It is crucial in such systems that the software is designed with a
sound architecture. A good architecture not only simplifies construction of the initial
system, but even more importantly, readily accommodates changes forced by a
steady stream of new requirements. In this paper, we describe a set of constructs that
facilitate the design of software architectures in this domain. The constructs, derived
from field-proven concepts originally defined in the ROOM modeling language, are
specified using the Unified Modeling Language (UML) standard.

Modeling Structure

The structure of a system identifies the entities that are to be modeled and
the relationships between them (e.g., communication relationships, containment
relationships). UML provides two fundamental complementary diagram types for
capturing the logical structure of systems: class diagrams and collaboration diagrams.
Class diagrams capture universal relationships among classes— those relationships
that exist among instances of the classes in all contexts. Collaboration diagrams
capture relationships that exist only within a particular context— a pattern of usage for
a particular purpose that is not inherent in the class itself. Collaboration diagrams
therefore include a distinction between the usage of different instances of the same
class, a distinction captured in the concept of role. In the modeling approach
described here, there is a strong emphasis on using UML collaboration diagrams to
explicitly represent the interconnections between architectural entities. Typically, the
complete specification of the structure of a complex real-time system is obtained
through a combination of class and collaboration diagrams.

Specifically three principal constructs for modeling structure:

· capsules
· ports
· connectors

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