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POPractical example of architecture using EBC?
 

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    <p>I was intrigued by Robert Martin's talk about <a href="http://confreaks.net/videos/759-rubymidwest2011-keynote-architecture-the-lost-years">"Architecture: The Lost Years"</a>. In it he discusses the Entity, Boundary, Control design pattern on which MVC is based. I love the idea of deferring architectural decisions. He described deferring the decision about how to implement the DB layer in his own wiki app FitNesse. I have organically deferred decisions like this in my own coding, though there wasn't a preconceived modular design that brought this about.</p> <p>I want to better understand this EBC architecture (which seems closely related to DCI) from a practical standpoint so that I can begin using in a small project. I want to capitalize on "deferring decisions" and the ability to swap out aspects of the design like the UI.</p> <p>Rails, for example, uses a form of EBC (MVC) but it's so heavily baked in that one could not easily substitute an alternate UI thus converting a Rails app to a console app or a desktop app. The intriguing thing about design for me is this ability to transform applications by swapping one thing out and plugging another in. That is, I wonder at the idea of designing an architecture so that one can, in a manner of speaking, swap out the UI or the persistence layer. I feel that if the architecture is well designed, the coupling will be low, and such a feat will be within grasp. </p> <p>I've ordered <a href="http://rads.stackoverflow.com/amzn/click/0201544350">the book</a> by Ivar Jacobson that Bob mentioned in his talk. I've search online quite a bit but all of the examples I've found show simple diagrams. I speak code. I would benefit more from looking over a few simple classes that demonstrate the concept and show how one might swap out one layer (UI, DB) for some other implementation through the use of boundary classes. </p> <p>If someone can't point me to a good resource illustrating this, would this be hard to whip up? Maybe we could use the standby example used in lots of software books: a video rental store (almost a relic these days). Please demonstrate how the UI or DB layer could be swapped. One thing that's confusing me is views. I can't tell from the diagrams I've seen if the views are the boundary classes themselves or if they just communicate with them. Also, Bob mentioned that the original intent of EBC was that we'd have lots of micro-views not a single macro-view (as we do in typical MVC); I'm curious what this might look like. (I prefer Ruby or JavaScript but, as beggars can't be choosers, any example would be fine.)</p> <p>Thank you.</p>
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    1. CORails is mostly model and controller; replace render and redirect with versions that accepted "txt" and "gui" formats you're basically done--actions only need a params hash. Just need additional handlers, and a less-HTTP-oriented routing/command definition system, although the current one could be co-opted by assuming request types are command modifiers. In the Java world things are decoupled like this all the time.
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    2. COThanks, Dave. I'm not after any sort of Rails retrofit. I just want to know some practical ways I might implement EBC in a greenfield app.
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    3. COI understand; I'm simply saying that making Rails do that wouldn't be the Herculean effort it appears at first. But this is a pretty nebulous question--as long as the layers are separated, it's all pretty straight-forward. What, precisely, are you looking for, and what would constitute a "successful" implementation?
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