Abstract:

This book examine architectures for software systems as well as better ways to support software development. We attempt to bring together the useful abstractions of systems design and the notations and tools of the software developer, and look at patterns used for system organization.

We present an introduction to the field of software architecture. Our purpose is to illustrate the discipling and examine the ways in which architectural design can impact software design. Our selection emphasizes informal descriptions, touching lightly on formal notations and specifications and on tools to support them.

The book serves two groups: First, professional software developers looking for new patterns for system organization. By identifying useful patterns clearly, giving examples, comparing them, and evaluating their utility in various settings, the book will sharpen their understanding and broaden their options. Second, students with interersts in software system organization.

Education in Software Architecture

This book can be used for a course, Architectures for Software Systems, that brings together the emerging models for software archtitectures and shows how to approach systems from an architectural point of view.

• Teaches how to understand and evaluate the design of existing software systems from an architectural persperctive,
• Provides the intellectual building blocks for designing new systems in principled ways using well-understood architectural paradigms,
• Shows how formal notations and models can be used to characterize and reason about a system design,
• Presents concrete examples of actual system architectures that can serve as models for new designs

Abstract: Software architecture is receiving increasing attention as a powerful way to deal with the complexity of large software systems. It has emerged as a distinct form of abstraction for software systems with its own set of design issues, vocabulary, and goals. Like designers in other disciplines, software architects can gain significant leverage by using powerful design environments and tools. Powerful design tools generally encapsulate a relatively small amount of design expertise that provides the important functionality of the tool within a relatively large support infrastructure. In this position paper I argue that in order to make the development of specialized architectural design tools practical it must be relatively easy and inexpensive to capture and make use of the desired design expertise. I then briefly describe an emerging approach for capturing this design expertise so that it can be used to incrementally configure architectural design environments.

Abstract: A question that frequently arises for architectural design is 'When can I implement a design in style S1 using a design in style S2?' In this paper I propose a technique for structuring a solution to this kind of problem using the idea of substyles. This technique leads to a two-step process in which first, useful subsets of a family of architectures are identified, and second, refinement rules specific to these subsets are established. I will argue that this technique, in combination with an unconventional interpretation of refinement, clarifies how engineers actually carry out architectural refinement and provides a formal framework for establishing the correctness of those methods.

Abstract: Dynamically composed systems are able to incorporate new components as they execute. Therefore, configurations of these systems are not fully elaborated until at least the time that they are executed, and they are perhaps never fully elaborated. Such incomplete configurations are termed partially bound configurations. Although partially bound, it is still important to be able to analyse these configurations to ascertain whether they meet certain assumptions about their composition. We are endevouring to provide such support for the construction of dynamically composed systems through the application of configuration management concepts. One way in which these concepts can be applied in this domain is to explicitly state such assumptions and hence be able to validate partially bound configurations against these assumptions; in this way, inconsistencies can be reported as soon as they arise. This paper disucsses the issues involved in providing this kind of consistency mechanism for dynamically composed systems.

Abstract: Although numerous mechanisms for promoting software reuse have been proposed and implemented over the years, most have focused on the reuse of implementation code. There is much conjecture and some empirical evidence, however, that the most effective forms of reuse are generally found at more abstract levels of software design. In this paper we discuss software reuse at the architectural level of design. Specifically, we argue that the concept of 'architectural style' is useful for supporting the classification, storage, and retrieval of reusable architectural design elements. We briefly describe the Aesop system's Software Shelf, a tool that assists designers in selecting appropriate design elements and patterns based on stylistic information and design constraints.

Abstract: Software architecture is receiving increasingly attention as a critical design level for software systems. However, the current practice of architectural description is largely informal and ad hoc, with the consequence that architectural documents serve as a poor communication mechanism, are difficult to analyze, and may have very little relationship to the implemented system. In an attempt to address these problems several researchers have experimented with formalisms for architectural specification and modelling. One such formalism is Wright. In this paper we show how Wright can be used to provide insight into an architectural design by modelling a prototype implementation of part of the AEGIS Weapons System.

Abstract: The ability to update a software system as it is being used is increasingly important and manifests itself in systems that must be maintained while executing, in systems where choices about which components comprise a system are deferred until their use, and where systems can be customised. Systems that fit one or more of these characteristics we call Dynamically Composed Systems (DCSs). Although some attention has been given to providing tools to support dynamic updates, and models of such dynamic updates have been constructed, little work as been done in examining this from a configuration management perspective. This paper describes a model of configuration management for dynamically composed systems, based on an existing model of configuration management for statically composed systems. The model includes a dynamic configuration description language, DCDL, and a formalization in terms of many-sorted algebraic specification techniques. The use of this model to design tools to support configuration management for dynamically composed systems is then discussed.