Saturday, October 17, 2009

OPL Layered Systems

Similar to the OPL Pipes & Filters pattern, the OPL Layered Systems pattern is considerably simpler and quicker to grasp than the previously presented pattern.  The previous pattern pointed out (and the OPL pattern omitted) that designing a good error handling system can be difficult in layered systems.  The OPL pattern made more explicit notice of the performance implications, and was more prescriptive in defining how the number of layers should be managed, whereas the previous presentation simply stated that "crossing component boundaries may impede performance".  I'm not sure if it's a strength or weakness of the OPL pattern, but the previous presentation details how to go about deriving a layered architecture, whereas the OPL pattern does not.  I guess this would be an argument for what the contents of a pattern should be.  It's been my feeling, however, that a pattern should read like a short encyclopedia entry--giving enough information to understand the basics, and deferring specific non-core details to other texts.  The OPL pattern does this, whereas the previous presentation goes into considerably more depth.  This may be due to the difference of one being an online library of patterns and the other being a chapter in a book, but to describe the best way to get a grasp of a large number of patterns, the former is more expeditious.

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