The disadvantage of a small conference is that speakers tend to drop out more frequently than you’ll find in large conferences, and this afternoon my first choice didn’t show. However, it had been a tough choice in any case, so I was happy to attend the session with Rob Cloutier of Stevens Institute of Technology on patterns in enterprise architecture.
The analysis of patterns has been around along time in mathematics and engineering, but they’re often difficult to capture and reuse in real life. There are some real business drivers for enterprise architecture patterns: much of the knowledge about systems is still gathered through artifacts, not patterns, making it difficult to reuse on other projects. It also tends to control complexity, since systems are based on standard patterns, and creates a common syntax and understanding for discussing projects. This has the impact of reducing risk, since the patterns are well understood.
Patterns are not created, they’re mined from successful projects by determining the elements contributing to the success of the projects.
In an enterprise architecture sense, there’s the issue of the level of these patterns; Cloutier’s premise is that you define and use patterns relative to your scope within the architecture, so may be a system architecture pattern. He laid out a topology of patterns relative to the views within the Zachman framework: organization, business and mission patterns at the contextual/scope level; structure, role, requirements, activities and system processes at the conceptual/enterprise model level, system analysis, system design, system test, software architecture, software analysis, software requirements, hardware requirements, hardware design and operational patterns at the logical/system model level, and so on. He focused primarily on the five patterns in the enterprise model level.
He walked through an example with use cases, generalizing the purchase of a specific item to the purchase of any product: the actors, functions and data flow can be generalized, then adapted to any similar system or process by changing the names and dropping the pieces that aren’t relevant. He listed the characteristics of a pattern that need to be documented, and pointed out that it’s critical to model interfaces.
He showed the analysis that he had done of multiple command-and-control systems to create a command-and-control pattern containing four basic steps in an IDEF model — plan, detect, control and act — with the input, outputs, strategy and resources for each step. In fact, each of those steps was itself a pattern that could be used independently.
He had an interesting analogy of the electricity and distribution system as a service-oriented architecture: you can plug in a new device without notifying the provider, you might be served by multiple electricity producers without knowing, your usage is metered for your service provider to bill you for the usage, and the details of how electricity is generated is generally not known to you.
Like any enterprise architecture initiative, the development of EA patterns is often considered overhead in organizations, so may never be done. You have to take the time up front to discover and document the pattern so that it can be reused later; it’s at the first point of reuse where you start to save money, and subsequent reuses where it really starts to pay off. Although many examples of software patterns exist, enterprise architecture patterns are much rarer: Cloutier is researching the creation of an EA pattern repository in his work at Stevens Institute of Technology. Ultimately, the general availability of enterprise architecture patterns that have been created by others — a formalization of best practices — is where the real benefits lie, and can help to foster the acceptance of EA in more organizations.
