Working With Data in Flex-2

When retrieving data, one needs to know the structure of XML being fetched. In order to form a collection out of the same on needs to point to the repeating structure. For eg. in the following XML:
<parent>
<child>
<name>child1</name>
<id>0</id>
</child>
<child>
<name>child2</name>
<id>1</id>
</child>
<child>
<name>child3</name>
<id>2</id>
</child>
<child>
<name>child4</name>
<id>3</id>
</child>
</parent>
we would have some function:

[Bindable]
private var resultList:ArrayCollection=new ArrayCollection();

public function getResult(event:ResultEvent):void{
resultList = event.result.parent.child;
}

In this case child is the repeating unit.
When using a list-based control we could directly specify the data from this xml as follows:
<mx:List id="id" rowCount="3" dataProvider="{resultList}" labelField="name"/>
Note that for labelField we have directly specified the name of the node to be used.

The actual call will happen only when the send method is invoked using the id given to HTTPService class. It is prudent to call it on creationComplete event of application if data is to be used application wide. Else on creationComplete of the specific ui objects.

Always use collections instead of arrays for data-binding. Much more useful. By default complex data-structure is returned as an ArrayCollection. Multiple control enable display datastructures using the dataProvider property. List-based controls (List,Tree,DataGrid,TileList,ComboBox) use this property for sure. dataProvider control have a lot of advantage in the sense they are dynamic and can be used to populate multiple controls. UI control data-binding does not happen with AS2.0 Array. You can pass the array to creation constructor of a collection to form a collection with the array elements.

Questions:

1. What is the advantage of using collections instead of arrays for data-binding?
2. Explain usage of HTTPService with an example.
3. When does the call to the URL mentioned in HTTPService happen?