Hitchhiker's Guide to Software Architecture and Everything Else - by Michael Stal

Saturday, February 28, 2015

Are Patterns like Mummies?

In 1994, the Gang of Four, Erich Gamma, Richard Helm, Ralph Johnson, John Vlissides published their groundbreaking book on design patterns. At almost the same time we were creating the first POSA book (Pattern-Oriented Software Architecture) which was eventually published in 1996. The software engineering community got flooded by the Pattern Wave. And soon there arrived an inflation of pattern books, some of them excellent, but many of them of mediocre quality.

I remember, that almost every software development magazine addressed patterns regularly and enthusiastically in the Nineties. The GoF became the Beatles of architects and developers. And most experts anticipated a myriad of new patterns rising at the horizon.

Actually, several pattern books have been published until now, but without the impact the GoF had. If you ask software engineers about the patterns they know, almost all will mention GoF patterns, many may illustrate some POSA patterns as well, and only a few will come up with other patterns such as those in Martin Fowlers book on Enterprise patterns.

This could suggest, that no other important patterns can be found in software habitats anymore, because GoF already got them all. But even if this were the case for general purpose design patterns, shouldn't there be some excellent patterns lurking in more specific domains? Pattern experts have tried to come up with complete pattern languages for their domains. In theory, such pattern languages are beneficial. In practice, it is impossible to cover a medium to large-sized domain with a pattern language because of the inherent complexity involved. Thus, it is not surprising that existing languages cover only tiny domains or fail to completely cover larger domains.

Does the whole universe only know the GoF patterns and that's it? In this case the seminal GoF book would be the holy grail of software development. If not, where do all the unknown patterns hide?

Let us assume we are asked to improve the GoF book, what exactly would we change. Patterns like the Null Object Pattern or the Extension Interface pattern (see POSA Vol. 2) could be added, the Singleton pattern removed and other patterns such as Abstract Factory improved. Patterns are not carved in stone but subject to future changes, albeit not with a high evolution speed.

If you look at patterns from 30000 feet, you'll recognize that there are some benefits of patterns not related to coding.

Pattern forms are a good mental tool to document design. For example, they comprise a name, a context, a problem with forces, and a solution. This helps document all kinds of architecture decisions in a structured way

Patterns are also applicable to document best practices for transformations, data representations, and many other topics. For example, each refactoring can be considered a transformation pattern. Best Practices are ideal candidates for patterns

Patterns introduce an idiomatic viewpoint, as they define a language. Effective usage of software platforms in terms of best practices for frameworks, libraries, APIs and protocols are idiomatic as well. Experience shows that idiomatic approaches help better understand structures and concepts. In software engineering all structures are idiomatic. Languages change and so do Patterns.

The value of patterns is not their content, but also their usage as good mental tools, with the capability of addressing all activities. Patterns help share best practices with others. They unfold a language of idioms that provide understandability, maintainability.

Patterns are dead. Long live patterns.

- Posted using BlogPress from my iPad



  • I liked the head first design patterns which dates back to the 2004. Now 10 years later, I'm wondering if there are newer, updated references that I should get my hands on.

    Welcome back btw.

    By Blogger Vincent Ho, at 11:30 AM  

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