OTHER ARCHITECTURAL CONCEPTS

The following sections describe several other topics related to software architecture.

Architectural Style

A software architecture, or an architectural view, may have an attribute called architectural style, which reduces the set of possible forms and imposes a certain degree of uniformity on the architecture. The style may be defined by the selection of an architectural framework, by middleware, by a recommended set of patterns, or by an architecture description technique or tool.

Examples of architectural styles are pipe-and-filter, client-server, and event-driven styles.

Architectural Mechanism

An architectural mechanism is a class, a group of classes, or a pattern that provides a common solution to a common problem. It is used to give life ”that is, behavior ”to other classes. Mechanisms are found primarily in the middle and lower layers of an architecture. They are analogous to the standard heating conduits and plumbing fixtures that are available to the architect of a building. They provide a means of rapidly implementing desired solutions.

Examples of architectural mechanisms include a database management system (DBMS), an event broadcasting system, and a transaction server.

Architectural Pattern

A pattern addresses and presents a common solution to a recurring design problem that arises in specific design situations. Patterns document existing, well-proven design experience. They identify abstractions that are above the level of classes, instances, and components . They provide a common vocabulary and understanding of design principles and are therefore a means of documenting software architectures. Patterns are larger-scale than mechanisms are; patterns describe broad interactions of abstract design elements that help the architect and designers think about a complex problem in an intuitive shorthand.

Software architectural patterns are analogous to patterns of architecture in buildings . When someone says that a building is a skyscraper, immediately a mental picture of the kind of building and the kind of project leaps to mind. We know that the structure is made of steel and concrete and not of wood. The design includes elevators in addition to stairways.

Patterns and mechanisms provide the architect with a growing tool-kit for solving architectural problems. Just as building architects have evolved a representation and symbology of the various problems they encounter, so too have software architects evolved intellectual tools (and software tools) to manage the complexity of systems. Patterns and mechanisms play a growing part in this toolkit. ^[6]

^[6] See Frank Buschmann, R gine Meunier, Hans Rohnert, Peter Sommerlad, and Michael Stahl, Pattern-Oriented Software Architecture: A System of Pattterns . New York: John Wiley and Sons, 1996.

Examples of architectural patterns are Model-View-Controller (MVC) and Object Request Broker (ORB).