With the release of Visual Studio. Config.web files are human readable, XML files that are used to configure almost every aspect of your web applications. Handlers are instances of classes that implement the System. The ProcessRequest method takes an HttpContext object as a parameter and is where the developer of a HTTP handler begins to do his work. After a handler is developed, it is configured in the config.web file of the application.
Handlers accept requests and produce a response.
When the HTTP runtime sees a request for a file with the extension of .aspx the handler that is registered to handle .aspx files is called. This is the same way in which .asmx files are handled. The generated HTML page also provides the user with a way in which to test the web methods within the service. SDL is an XML based grammar for describing the capabilities of web services. SDL allows a web service to be queried by potential consumers of your service you can think of it as an XML based type library made available via the web.