SOA with .NET and Windows Azure : Web Services (ASMX and WSE)

XML Web Services (ASMX)

Web services were officially referred to as “XML Web Services” and were further termed with the ASMX acronym because, when developed with ASP.NET, their logic was placed into a file with the .asmx extension.

Specifically, this file contained:

• the ASP.NET @WebService directive

• code to implement the Web service or a reference to a file that implements the Web service logic (also known as the “code-behind” file)

The typical implementation for a Web service was contained in a code-behind file that is actually referenced using the @WebService directive, as follows:

Example 1.

<%
  @WebService
  Language="C#"
  CodeBehind="~/App_Code/DemoService.cs"
  Class="DemoService"
%>

The .NET API used to implement a Web service was contained in the System.Web.Services namespace. Classes and attributes from the namespace used to implement the Web service included:

• WebService attribute

• WebMethod attribute

Let’s briefly explain each.

The WebService Attribute

This attribute has to be applied to a class in order to designate it as a Web service, as follows:

Example 2.

using System;
using System.Web;
using System.Web.Services;
using System.Web.Services.Protocols;
[WebService(Description = "Demo Service",
            Namespace = "http://www.example.org")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
interface IDemoService
{
    string Greet();
}
public class DemoService : System.Web.Services.WebService, IDemoService
{
[WebMethod]
public string Greet() {
    return "Hello World";
}
}

In this example, the Web service was defined using a .NET interface definition, thereby decoupling the service definition from the service contract (which, incidentally, makes the service easier to manage, reuse, and migrate to WCF).

The WebService attribute accepted three parameters, as shown in Table 1.

The WebMethod Attribute

The WebMethod attribute was used to tag operations in a class that could be exposed by a Web service. For an operation to be available to the service consumer it had to be a public method and further had to be annotated with a WebMethod attribute, as was shown in Example 2.

The WebMethod attribute contained optional parameters that could be used to customize each operation, as listed in Table 2.

Web Service Enhancements (WSE)

ASMX primarily supported the creation of Web services based on SOAP and WSDL. It originally did not include support for other WS-* industry standards, most notably WS-Security.

Microsoft subsequently released Web Services Enhancements (WSE) as an extension for the initial ASMX platform. WSE added support for various WS-* standards that introduced new features, such as message-layer security, content-based routing, and support for policies (which corresponded to the WS-Security, WS-Addressing, and WS-Policy standards respectively).