In software design, designers frequently encounter a problem that they have solved before on a previous project. Often the context of the problem is different; it might be a different application, a different platform, or a different programming language. Because of the different context, a designer usually ends up redesigning and reimplementing the solution, thereby falling into the trap of “reinventing the wheel.” The field of software patterns, including architectural and design patterns, is helping developers avoid unnecessary redesign and reimplementation.

In software development, the field of design patterns was popularized by Gamma, Helm, Johnson, and Vlissides in their book Design Patterns (1995), in which they described twenty-three design patterns. Later, Buschmann et al. (1996) described patterns that span different levels of abstraction, from high-level architectural patterns through design patterns to low-level idioms.

This chapter describes several software architectural patterns that can be used in the development of real-time embedded systems. Section 11.1 provides an overview of the different kinds of software patterns. Sections 11.2 through 11.7 describe the different software architectural patterns, with Sections 11.2 through 11.4 focusing on patterns that address the structure of the software architecture and Sections 11.5 through 11.7 discussing patterns that address the message communication among distributed components of the software architecture. Section 11.8 describes how to document software architectural patterns using a standard template. Section 11.9 describes how to apply software architectural patterns to build a new software architecture.

SOFTWARE DESIGN PATTERNS

A design pattern describes a recurring design problem to be solved, a solution to the problem, and the context in which that solution works (Buschmann et al. 1996, Gamma et al. 1995). The description is in terms of communicating objects and classes customized to solve a general design problem in a particular context. A design pattern is a larger-grained form of reuse than a class. A design pattern involves more than one class along with the interconnection among the different classes.

After the original success of the design pattern concept, other kinds of patterns were developed. The main kinds of reusable patterns are given below:

1. • Design patterns. In a widely cited book (Gamma et al. 1995), design patterns were described by four software designers – Erich Gamma, Richard Helm, Ralph Johnson, […]