Programming .NET 3.5

Implementing Web Services

It is important to recognize that a web service is just one of many service implementations. That said, the increasing ease with which one can create a web service has been a catalyst for the explosion of SOA implementations in recent years. It is the basic nature of the web service, "a programmable application component accessible via standard web protocols," that is helping deliver on the promise of SOA. In a nutshell, you can think of SOA as having three components:

• Standard protocols—HTTP, SMTP, FTP with HTTP

• Service description—WSDL and XSD

• Service discovery—UDDI and other "yellow pages"

The protocol stack for WCF's implementation of web services is outlined in Figure 10-3. Web services typically flow from top to bottom (discovery, then description, then messaging).

To consume a web service, you need to know that it exists, what it does, what kind of interface it offers, and so on. You should also note that with WCF, you are strongly encouraged to use UDDI for publishing your web service's metadata exchange endpoints, and to query the service directly for the WSDL document and policies. After all of this has been accomplished, your client can invoke the web service via SOAP.

We'll start at the bottom of the stack and work our way back up.

SOAP: More Than Just a Cleanser

SOAP is the preferred protocol for exchanging XML-based messages over computer networks using the standard transport mechanisms outlined in the preceding section. SOAP is the top end of the ...