Date: 2004-03-12T11:34:31
Editor: AaronFarr <[EMAIL PROTECTED]>
Wiki: Apache Avalon Wiki
Page: SeparationOfConcerns
URL: http://wiki.apache.org/avalon/SeparationOfConcerns
explaination of SoC -farra
New Page:
= Separation Of Concerns =
Separation Of Concerns (SoC) is a DesignPattern which states that problems can be
seperated into a set of components each of which focus on only one core concern.
== A Simple SoC Example ==
In order to understand SoC, let's look at a simple example: Java Servlet Programming.
When Java servlets first arrived on the scene, it wasn't too hard to find web
application designed like this:
{{{
+-------------------------------------+
___________
+----------+ | SERVLET | (
)
| | | o parses request |
|`----------|
| BROWSER | <== HTTP ==>| o retrieves data from database | <-- JDBC -->|
|
| | | o creates HTML results | |
DATABASE |
+----------+ | | |
|
+-------------------------------------+
\-----------/
}}}
While for simple applications this design worked just find, it quickly became
unmanagable as the problem scales. Any change to the HTML look and feel would require
recompiling the servlet. Business logic and display logic was closely tied together.
This is an example of no seperation of concerns. Everything jumbled together in one
monolithic heap.
Thankfully designs and technology evolved and we soon saw a new design pattern being
applied to Java web applications -- Model View Controller (MVC). The MVC appraoch
divides the single monolithic servlet into a Model (handles business data and rules),
a View (handles presentation logic), and a Controller (parses request and controls
execution flow). Various web frameworks built on this MVC idea such as Jakarta
Turbine and Jakarta Stuts. So instead of the one servlet above, we end up with:
{{{
+------ web application ---------+
| |
+------------+ | +---------------+ |
| | === HTTP ===> +--> | CONTROLLER | --| |
___________
| | | +---------------+ V | (
)
| BROWSER | | +-------+ |
|`----------|
| | | +----------+ | MODEL | ------JDBC---->|
|
| | <=== HTTP === |----| VIEW | +-------+ | |
DATABASE |
+------------+ | +----------+ <-------| | |
|
+--------------------------------+
\-----------/
}}}
As we can see MVC is a type of Separation of Concerns. There are numerous advantages
to this approach of software design, one of which is the easier application of
[wiki:WhatIsIoC Inversion of Control].
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