Mechanisms for Automatic Web Service Composition

Background

In this section, we introduce some web service composition related terms and standards used in this chapter.

WSDL (Web Service Definition Language) is an XML-based language used for describing web services as a collection of endpoints that operate on messages that contain procedure or document-oriented information. When a client program connects to a web service, it can read the WSDL to determine what functions are available to be used. More information can be found in (Chinnici, 2007). WSDL is often used in conjunction with the Simple Object Access Protocol (SOAP).

SOAP is a protocol for exchanging XML-based messages over the internet. It defines an extensible messaging framework containing a message structure that is exchanged over different application-level protocols, such as HTTP or SMTP. SOAP is used in the context of web services to perform remote procedure calls and it has gained a considerable broader user base than CORBA or DCOM due to the ability of HTTP and HTTPS traffic to pass through firewalls. Additional information on SOAP can be found in (Gudgin, 2007).

UDDI (Universal Description, Discovery and Integration) (OASIS, 2008) is platform-independent XML-based registry that provides interfaces for publishing and searching services, defining thus how these services interact over the internet. UDDI is probed by SOAP messages and also provides access to WSDL documents describing the protocol bindings and message formats required to interact with the services listed in its directory.