CQS – A Literary Perspective

If you have been following the DDD and DDDD waves, you’re sure to have come across the CQS pattern. When I first heard of this, I immediately liked it but thought it was surely a pattern for very, very large systems. Most systems probably don’t need CQS, but this morning over breakfast, a discussion with my wife on child learning patterns made me rethink this.

We have a friend whose children have grown at very different rates of reading comprehension and writing skill. The interesting part is that the rates are nearly opposite from one another. The one with excellent reading comprehension does not excel at writing while the other is and excellent writer but has trouble reading. I found this somewhat strange. After all, logically, I would think that the one who reads should be able to write better. But that’s not the case. No one can do everything best. The same is true of databases.

This is such a true statement that in the Collective Intelligence session at the Houston ALT.NET Open Spaces, four distinct database tiers were promoted for proper separation of concerns to allow each tier to most effectively perform its task. Is this necessary for every application? Probably not, but as we move toward a more virtualized server world, the cost is really swinging in the favor of using multiple databases for reading and writing concerns. This may break the YAGNI principle, but I think we may often find that simplest may really be the best, simplest, smallest part that can fit the bill. (I’m sure that last statement will really ruffle feathers, but that’s where I am atm.)

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