Metacat

<h2>Model-View-Controller design pattern</h2>

<p>

A Mapbuilder configuration file closely follows the Model-View-Controller (MVC)

design pattern.

There are many descriptions of the MVC design pattern 

<a href="http://www.google.ca/search?hl=en&q=Model+View+Controller+design+pattern">available;</a>

a brief description of it as it applies to Mapbuilder is provided below.

It is a very useful design pattern for web applications because it provides

good separation between the information content, the presentation of that

information and the application state.

</p>

<div id="mainMapPane" style="float:right">

<img src="http://mapbuilder.sourceforge.net/mapbuilder/docs/design/images/mvc.gif"/>

</div>

<p>

A <span class="regbld">Model</span> represents the information of the application,

typically in the form of an XML document retreived from a web service or in the

the form of a static file at a URL.

Models provide "get" methods to retrieve particular pieces of information or 

state and "set" methods to update the information and state of the model.

When set methods are used, views are notified of the change by calling 

listeners that can be registered with the model.

</p>

<p>

A <span class="regbld">View</span> is a representation of the information 

in a model.

Views can register themselves with a model to be notified of changes in the model

that may affect the view.

This is typically using "listener" callback methods which are called for 

various event types.

Views may also provide means to send user gestures (e.g. mouse clicks) to a 

controller.

In Mapbuilder, views are called widgets.

</p>

<p>

A <span class="regbld">Controller</span> translates interactions with the view 

into actions to be performed by the model.

Controllers modify the information and state of a model.

In Mapbuilder, views are called tools.

</p>

<p>

The separation of model and view allows multiple views to use the same model. 

Consequently, model components are easier to implement, test, and maintain, 

since all access to the model goes through these components.

This also makes it easy to extend because you can simply write a view and 

some controller logic and wire them into the existing application.

</p>

<p>

Mapbuilder can dynamically retrieve and store many different models within the 

same web application.

In order to provide some structure to the various models that can be realized, 

a model may contain an array of other models in a parent-child replationship.

For example, a WFS DescribeFeatureType response model can be logically represented

as a child of a WFS GetCapabilities model since they are initimately related.

</p>

<p>

In the Mapbuilder object-oriented design, models, widgets and tools are all 

realized as object instances in Javascript.

The list of objects to be created and the relationship between them is

specified in the configuration file.  

Properties are also optionally assigned to each object in the configuration file.

The actual objects that mapbuilder supports and the properties that can be 

assigned to them is detailed in the <a href="docs/register">Component register.</a>

</p>

<p>

</p>

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