Introduction to XML Web Services Created with ASP.NET

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1

An XML Web service is a programmable entity that provides a particular function, such as application logic, and is accessible to systems using Internet standards such as XML, HTTP, and SOAP. Applications written in any language and running on any operating system can call XML Web services.

An XML Web service can be used internally by a single application or exposed externally over the Internet for use by any number of applications. Because it is accessible through a standard interface, an XML Web service allows heterogeneous systems to work together as a single web of computation. One of the core characteristics of an XML Web service is the high degree of abstraction that exists between the implementation and consumption of a service. Because an XML Web service is created and accessed using XML-based messaging, the XML Web service provider and the client need no knowledge of each other beyond inputs, outputs, and location.

The XML Web services infrastructure provides a discovery mechanism to locate XML Web services, a service description for defining how to use those services, and standard wire formats for communication.

Discovery is the process of locating one or more documents that describe a particular XML Web service using the Web Services Description Language (WSDL). Once a service is found, the WSDL document provides a description of the interactions that the service supports. XML Web services communicate using open wire formats, which are protocols that can be understood by any system capable of supporting the most common Web standards. SOAP is the key protocol for XML Web service communication.

ASP.NET enables you to build and publish XML Web services using the same programming constructs that are used to build and publish ASP.NET Web pages. XML Web services created with ASP.NET use the industry standards shown in the following table.

Industry standard	Use in XML Web services created with ASP.NET
XML	The text format used when communicating with XML Web services using SOAP. When communicating with XML Web services using the HTTP-GET and HTTP-POST protocols, XML is used to encode the response.
SOAP	An XML-based message exchange protocol used for communication between XML Web services and their clients.
Web Services Description Language (WSDL)	Describes the contract of messages that an XML Web service can interpret when communicating with an XML Web service client.
XML Schema Definition language (XSD)	Provides a universal type system, allowing data types to be defined and passed across platforms. For an XML Web service, XSD defines the structure and data types for the XML encapsulated within a SOAP message sent to and from an XML Web service.
application/x-www-form-url encoded	A MIME type used for encoding parameters on a URL. This encoding is used for encoding request parameters to XML Web services using the HTTP-GET and HTTP-POST protocols.