OTHER STUFF
There’s much more to UML 2.0 than we’ve talked about here, but probably the most important thing to remember is that your UML 1.x models will remain completely valid in most cases. There’s been very significant redesign and re-redesign of the internal metamodel structure. This continues as technical details are hashed out, rethought, and hashed out again. Many small, and yet important (to some people), changes are being made to associations, association subsetting, merging actions and activities, and so on. The fundamental nature and expressiveness of the UML remains. However, three large-scale things must be briefly mentioned:
First, interaction overview diagrams have merged activity diagrams with sequence diagrams, allowing an activity diagram to serve as a "master chart" for a set of sequence diagrams. This allows you to construct a "map" of sequence diagrams and navigate easily among them.
Second, activity diagrams in UML 1.x have the same semantic basis as statecharts. In other words, they can say exactly the same things although they use a different notation. In UML 2.0, activity diagrams are now based on Petri net token-based semantics, rather then finite state automata, and are more expressive. While this is less important for computational algorithms, it aids in process modeling.
Finally, UML 2.0 now includes Flow Diagrams that can show data flow among structural elements (object roles). Note that this is similar to, but not the same as message flow on collaboration diagrams. But for those modelers who wish to do data-flow-diagram (DFD)-style models, you will be able to do this with the UML as illustrated in Figure 9.
The UML 2.0 has its basis firmly set upon UML 1.x. Most UML 1.x models are valid in UML 2.0 However, UML 2.0 has a number of significant, if incremental, improvements for architectural modeling. These include structured classes, elaborated interfaces and ports, scalability, interaction fragments and operators, and enhanced modeling of behavior over time. And let’s not forget timing diagrams. However, you don’t have to worry about these new features if you don’t want to. You can still build significantly complex systems using only three diagrams—class, sequence, and state diagrams.
While the final release of the UML 2.0 is still at least some months away, we know some of its major features and characteristics. And we—as developers of complex, next-generation real-time and embedded systems—have a lot to look forward to.
Bruce Powel Douglass is the chief evangelist at I-Logix Inc. (www.ilogix.com), Andover, Mass. He holds a PhD from the University of South Dakota in Vermillion. Douglass can be reached at bpd@ilogix.com.