A Web service is a set of related application functions that can be programmatically invoked over the Internet. Businesses can dynamically mix and match Web services to perform complex transactions with minimal programming. Web services allow buyers and sellers all over the world to discover each other, connect dynamically, and execute transactions in real time with minimal human interaction.
Web services might be anything, for example, theatre review articles, weather reports, credit checks, stock quotations, travel advisories, or airline travel reservation processes. Each of these self-contained business services is an application that can easily integrate with other services, from the same or different companies, to create a complete business process. This interoperability allows businesses to dynamically publish, discover, and bind a range of Web services through the Internet.
Web services are part of an emerging technology that offers the dual promise of simplicity and pervasiveness. Much of the simplicity is due to the common XML (Extensible Markup Language) foundation that underlies most Web service protocols. Web services provide a ubiquitous model for offering business services over the Internet as well as within organizations. Web services are of particular interest for their ability to incorporate third-party applications or legacy applications.
In the most primitive sense, Web services can be viewed as any mechanism by which an application service may be provided to other applications on the Internet. Web services are described in WSDL (Web Services Description Language). The WSDL description may be registered in the UDDI (Universal Description, Discovery, and Integration) repository. UDDI provides a set of application programming interfaces (APIs) to register and search for Web services.
Web services may be informational or transactional. That is, some services will provide information of interest to the requestor, whereas other services may actually lead to the invocation of business processes. Informational Web services available today range from simple weather or stock-quote services to the access of nucleotide sequence data or corporate in-formation. Transactional Web services are being defined by organizations such as ebXML and XML.org to facilitate standardization of business-to-business processes.