Tuesday, March 30, 2010

Evolving Gracefully - Example I

In my posts, "What is Architecture", Part I and Part II, I argued that architecture is essentially what enables a system to evolve gracefully and traverse an optimal path in response to changes (requirements, assumptions, context, inputs etc.). In this post (and in a few more) I give examples of such changes and possible optimal/graceful (or non-optimal/disruptive) responses of a system.

Take "Accessibility Requirement" as an example. Few software systems are designed with the explicit goal of accessibility as one of the main architecture and design goals. However, some systems at some point must comply to certain accessibility standards and guidelines (it is good usability practices, the right thing to do, good business and the law) - see a very good introduction to accessibility from WebAIM.org here.

Now, if some one came one morning and asked you to make sure every image in every single HTML page of your site has an alt tag, what would be your response? Remember this maybe 1000s or image tag in 10s or 100s of applications produced by developers across three continents.

If your architecture (and the design and implementation of it) decoupled model construction from actual rendering, and a centralized rendering engine that takes a data structure (such as DOM) and uses a rendering strategy to produce XHTML, then your architecture (and you) has no problem responding to this new requirement easily. You'd simply make sure that when the render visit an element, it finds an alt attribute. This is an optimal response to change. Although the system was not particullary designed with accessibility in mind, since it was built based on the right architecture, it can evolve to accommodate change.

However, if the 1000s HTML pages on your site are produced by 100s of JSP scripts, a few PHP scripts, some XSL, a few instances of dynamically created tags in JavsScript etc. You would have a nightmare on your hand. This is an example of architecture that can not evolve ...


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