2.4 Zachman Framework

Many authorities in the software industry have thoroughly considered the needs discussed here. Two leading meta-architectural frameworks guide the development of software system architecture. One of the popular frameworks originated at IBM and is called the Zachman Framework. The Zachman Framework predated the popularity of object orientation and took the perspective of separating data from process. The Zachman Framework includes six information system viewpoints as well as five levels of design abstraction. The original Zachman Framework published in 1987 contained viewpoints for the network, the data, and the process of the information system [Zachman 1997]. A subsequent revision introduced three additional viewpoints. The current framework resembles the set of traditional journalistic questions, which include who, what, when, why, where, and how. Each viewpoint in the Zachman Framework answers a chief set of questions to ensure that a complete system engineering architecture is created.

The Zachman Framework formed a matrix of architectural descriptions that are also organized in terms of levels. There are five levels of description above the information system implementation. They range from architectural planning done by individual programmers at the finest grain to the overall enterprise requirements from the investors' perspective of the information system. In total, the Zachman Framework identifies thirty architectural specifications, which provide a complete description of the information system. In practice, no real-world project is capable of creating these thirty or more detailed plans and keeping them all in synchronization. When the Zachman Framework is applied, systems architects partition the viewpoint into various categories and create architectural specifications that cover some or all of the different Zachman descriptions without having to create the large number of individual specification documents that the Zachman Framework spans. One example is a very successful architectural initiative by the U.S. Department of Defense (DOD) called the C4ISR architectural framework, where C4ISR stands for Command and Control, Computers, Communication, Intelligence Surveillance, and Reconnaissance. The C4ISR architectural framework is used to describe DOD information technology at the highest echelons of the organization. The primary benefit in this case is that different service organizations and agencies can communicate their architectural plans through common-viewpoint description.

Beyond the Zachman Framework, object-oriented architects have discovered additional needs for defining computational architecture and other viewpoints that are not obvious applications of the Zachman principles. The ISO has also considered these architectural issues. The ISO reference model for open distributed processing called RM-ODP was recently completed. This model belongs to a category of ISO standards called Open Distributed Processing. ODP is an outgrowth of earlier work by ISO in open systems interoperability. The Open Systems Interconnection (OSI) seven-layer reference model identified an application layer that provided minimal structure and guidance for the development of application systems. In fact, the seventh layer for application organizes remote procedure calls, directory services, and all other forms of application-level services within the same architectural category, without defining any particular structure or guidance for this significant category of functionality.