5 - Structural Modeling for Real-Time Embedded Systems with SysML and UML

Summary

This chapter describes how structural modeling can be used as an integrated approach for system and software modeling of embedded systems consisting of both hardware and software components. The structural view of a system is a static modeling view, which does not change with time. A static model describes the static structure of the system being modeled, first the static structure of the total hardware/software system followed by the static structure of the software system.

Since a class is a software concept describing a software element, a more general term is needed to refer to a system element. SysML uses the concept of a block as a system structural element, which is a broader modeling concept than a class that can be used to refer to a hardware, software, or person structural element. In this chapter, the term structural element is used to refer to either a block or class.

The SysML block definition diagram notation is used to depict the static model of the total hardware/software system and the UML class diagram notation is used to depict the static model of the software system. SysML block definition diagrams and UML class diagrams were first introduced in Chapter 2. For system modeling, this chapter describes system-wide structural modeling concepts including blocks, attributes of blocks, and relationships between blocks. For software modeling, this chapter describes software structural modeling concepts including classes, attributes of classes and relationships between classes. Software design concepts such as class operations (methods) are deferred to software class design as described in Chapter 14.

The objective of the model-based approach described in this chapter is to clearly delineate between total system (i.e., hardware and software) modeling and strictly software modeling, with a well-defined transition between the two modeling activities. This chapter starts with a brief description of static modeling, in particular the relationships between structural elements (blocks or classes) in Section 5.1. Three types of relationship are described: associations, composition and aggregation relationships, and generalization/specialization relationships. After the introduction to static modeling, this chapter addresses the categorization of blocks and classes using stereotypes in Section 5.2, structural modeling of the problem domain with SysML in Section 5.3, structural modeling of the system context in Section 5.4, hardware/software boundary modeling in Section 5.5, …