Beginning Web Development, Silverlight, and ASP.NET AJAX

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CHAPTER 5 ■ ASP.NET WEB SERVICES
document containing its response to you (this style of web service is more formally called
an XML web service).
Another interesting facet of modern XML web services is that the service describes
itself also using XML. Based on this description, you can craft your requests and understand
the responses you receive. Nowhere in this picture are you bound to a particular
web presentation technology; therefore, when using web services, you can (in theory at
least) present your data to clients that use a different technology base (such as Java 2
Platform Enterprise Edition [J2EE]), or conversely, consume data that is available on a
different technology base.
In this chapter, you’ll look at web services with ASP.NET. You’ll look into how to create
and consume them, and you’ll explore interoperability technologies that will ensure that
your applications can be consumed by others.
Web Services Architecture
XML web services are defined by the W3C as a software system designed to support
interoperable machine-to-machine interaction over a network. The XML Web Services
specification serves as the basis for communicating information that is well defined and
generally available for any technology that implements the specification. The concept
of computer-to-computer data communication isn’t new; technologies such as DCOM
(Distributed Component Object Model) and CORBA (Common Object Request Broker
Architecture) have had this functionality for some time. Where XML web services differ is
in how they achieve this goal. Instead of using a proprietary data representation, often
called a “wire protocol,” they use XML, which has become a leading standard for communicating
data across the network.
Web services come from the application of several different technologies. These are
as follows:
Hypertext Transmission Protocol (HTTP): This is the well-known means of clientserver
communication that the Internet is built on.
XML: This enables data to be encoded in a machine-readable, richly attributed
format.
Simple Object Access Protocol (SOAP): This is a variant of XML and is used to encode
requests to a service and response data from the service.
Web Services Description Language (WSDL): This is a variant of XML and is used to
describe a web service. This description can be interpreted by a client machine to
decipher how the SOAP document structure will be set up to talk to a specific server’s
web service.