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Web Services Developer's Guide
Introducing Business Process Server Web Services : Web Services standards

Web Services standards

Web Services are based on standard infrastructures, using XML to communicate across such standard protocols as HTTP, TCP/IP, SMTP or FTP. Because all communication is in XML, Web Services are not tied to any one operating system or programming language.
Web Services also use newer standards that include such terms as SOAP, WSDL, and UDDI. These Web Services-specific standards are described below:
*WSDL. The Web Services Description Language provides a standard XML-based language used to describe Web Services. You can use a WSDL document to capture service descriptions that determine the operations a Web service provides and to execute them. WSDL uses an XML format to describe network services as a set of endpoints operating on messages containing either document-oriented or procedure-oriented information. The operations and messages are described abstractly, and are then bound to a concrete network protocol and message format to define an endpoint.
*SOAP. Simple Object Access Protocol is a standard for an XML-based exchange of information between distributed applications, transferring data over such standard transport protocols as HTTP. SOAP is a lightweight, platform-independent protocol consisting of the following parts:
*An envelope that defines a framework for describing what is in a message and how to process it.
*A set of encoding rules for expressing instances of application-defined data types.
*A convention for representing remote procedure calls and responses.
*A binding convention for exchanging messages using an underlying protocol.
*UDDI. Universal Description, Discovery and Integration registry is a searchable directory of Web services that Service Requesters can use to search for Web Services and access WSDL documents. UDDI provides a distributed registry of businesses and their service descriptions implemented in a common XML format, and acts as a "Yellow Pages" service that defines a way to publish and discover information about Web Services.
In summary, UDDI enables users to publish and/or find specified web services; WSDL enables users to describe web services in a standard, accessible format; and SOAP enables users to bind and use the Web Services from an application. These Web Services-specific standards provide the infrastructure to publish (using WSDL and UDDI), find (using WSDL and UDDI) and bind (using WSDL and SOAP) Web Services in an interoperable manner.