Question

Suppose all that happens initially in a client swf is a user clicks a hyperlink in a text object of the swf, so this requests a “page” from the server. In response the server just modifies that existing swf in the client browser, by for example (?) invoking public functions of it, and possibly passing in as parameters the name of image or data files which were also downloaded in response to the URL request. The crucial part is that all that can happen initially in the SWF is a URL “page” request. Is this commonly done and if so, how.

Answer 1

Clicking on an hyperlink in AS3 will trigger a TextEvent.LINK event, you can then listen to this event and in your function proceed to call the relevant service which in turn will send you a response which you can use to update your swf data.

Check the docs here for the TextEvent class
http://www.adobe.com/livedocs/flash/9.0/ActionScriptLangRefV3/

Now, it all depends on what your link is, if it loads an XML ,then you can use the URLLoader class to load the XML data

 private function init():void
 {
     var tf:TextField = new TextField();
     tf.htmlText = "<a href='http://example.com/data.xml'>Update Data</a>";
     tf.addEventListener(TextEvent.LINK, clickHandler);
     addChild(tf);
 }

 private function clickHandler(e:TextEvent):void 
 {
    trace(e.type); // link
    trace(e.text); // http://example.com/data.xml

    var loader:URLLoader = new URLLoader();
    loader.addEventListener( Event.COMPLETE , dataLoaded );
    loader.load( new URLRequest( e.text ) );
 }

 private function dataLoaded(event:Event):void
 {
    trace( event.target.data );// xml content
    //from here you can then parse the XML & update your swf
 }