The term architecture is used here to describe the attributes of a system as seen by the programmer, i.e., the conceptual structure and functional behavior, as distinct from the organization of the data flow and controls, the logical design, and the physical implementation.
This isnt about structural relationships between components, its about hiding that structure and focusing instead on behavior. Nowadays, wed say it defines architecture as the properties of a class of objects. How did we get from external properties to internal structure? Thats largely the doing of Edsgar Dijkstra, when in 1968 he laid the foundations for the idea of software architecture. Theres a good discussion of this at the Software Engineering Institute (SEI) websitehttp://www.sei.cmu.edu.
When you consider enterprise architecture, things get even more curious. Neither IEEE nor The Open Group define enterprise architecture explicitly. The most commonly cited first use of enterprise architecture doesnt actually call it enterprise architecture, and thus doesnt define it.
John Zachman first applied the idea of architecture to an enterprise-wide (though IT-focused) scope in his paper A framework for information systems architecture (IBM Systems Journal, Vol. 26, No. 3, 1987). Note that Zachman did not call it enterprise architecture, rather he called it information systems architecture. Five years later he was still not calling it enterprise architecture, but somebody else was.
The first actual use of enterprise architecture I have found is by Steven Spewak in his book Enterprise Architecture Planning: Developing a Blueprint for Data, Applications and Technology (Wiley, 1992). Note that the subtitle limits the scope to data, applications and technology.
Spewak loosely defines architecture as being like blueprints, drawings or models. He defines enterprise by writing the term enterprise should include all areas that need to share substantial amounts of data.
More recent definitions of enterprise architecture tend to put less emphasis on architecture and more on the delivery of business value, in response to the pursuit of the perennially elusive business/IT alignment.
For example, researchers at the MIT Sloan Center for Information Systems Research (CISR) published Enterprise Architecture as Strategy: Creating a Foundation for Business Execution (Ross, Weill and Robertson; Harvard Business School Press; 2006), where they define enterprise architecture as:
The organizing logic for core business processes and IT infrastructure reflecting the standardization and integration of a companys business model.
And the Wikipedia entry for enterprise architecture defines it thus:
Enterprise Architecture is the description of current and/or future structure and behavior of organizations processes, information systems, personnel and organizational sub-units, aligned with the organizations core goals and strategic direction. Although often associated strictly with information technology, it relates more broadly to the practice of business optimization in that it addresses business architecture, performance management, organizational structure and process architecture as well.
As I said earlier, I am reminded of the blind men and the elephant. Is it possible to see the whole elephant for what it really is? Is there a single useful definition of our kind of architecture that encompasses all of these different perspectives and their implied needs? I believe there is. In my next article, Ill describe my quest for it.
Len Fehskens is The Open Groups vice president and global professional lead for enterprise architecture. He has extensive experience in the IT industry, within both product engineering and professional services business units. Len most recently led the Worldwide Architecture Profession Office at Hewlett-Packards Services business unit, and has previously worked for Compaq, Digital Equipment Corporation (DEC), Prime Computer and Data General Corporation.