From: "Guerry A. Semones" <gsemones@...>
Date: 2001-03-10T02:44:22+09:00
Subject: [ruby-talk:12342] Re: Understanding Design Patterns Was: GUI Toolkit for Ruby

<snipped some of Pete's comments>
> While someone could possibly build a really generic interface to all
of
> the libraries, I'd suggest that a clean separation between the
> presentation logic and everything else is a better way to go.
> 
> The Facade design pattern kind of explains this, but it is shown
much
> better in Martin Fowler's "Analysis Patterns" book. The idea is that
you
> provide a Facade that can be used to drive your application. Then
you
> craft whatever user interface you want (Command line or GUI) and
that
> then drives the application using the methods exposed by the Facade.
> 
> If you do this right it is then a relatively simple task to put a
> different user interface on the application.

This happens to be precisely what Ben Tilley was asking for in his
recent post to the GUI discussion.  I wholeheartedly agree.  

The Facade pattern according to Fowler: "A facade is a type that
provides a simplified interface to a complicated model" (Analysis
Patterns, p.247).  The Model-View-Controller (MVC) pattern essentially
tries to separate the model (data and logic) and the view (UI) with a
controller (which knows about both).  Please don't anyone slam my
definition, I'm sure its not sufficient, but I've got the flu and
other such excuses :-).

By combining the two, you get some really excellent benefits.  As you
said one can swap out the UI or provide multiple UI in front of the
business logic.  Also (here's my addition) one can write tests against
the business logic and not have to worry about testing business logic
tangled in the GUI.  

Most simply put, the GUI should not do much more than delegate calls
to non-GUI classes that do the real work.  The GUI code should deal
with GUI issues, the business logic should deal with business logic.  

We are currently doing a project where we've done just this.  All
business logic and validation are done separate from the GUI, and the
GUI just delegates back.  Most of the core business also delegates
back to a mid-tier.  The core point, however, is that we will be
taking the business and validation logic and put it, unchanged, into
an MVC designed web architecture: same code, same tests, different
interfaces.

Thanks,

Guerry

-- 
G. Semones, gsemones@treenleaf.com, http://www.treenleaf.com
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