Impact of the Internet and emergence of Web services

The emergence of the Internet as a business channel, many applications need to be made available over the Internet in some form or the other. This has led to the development of Web services. Web services are self-contained, applications that can be described, published, located, and invoked over networks. Web services encapsulate business functions, ranging from simple queries to full business process interactions. The services can be new or wrap around existing applications.

The following are the core technologies used for Web services:

• Extensible Markup Language (XML) is the markup language that underlies most of the specifications used for Web services. XML is a generic language that can be used to describe any kind of content in a structured way, separated from its presentation to a specific device.
• SOAP (originally an acronym for Simple Object Access Protocol) is an application-to-application protocol that isolates network, transport, programming language, and platform differences to allow a client to call a remote service without knowledge of how the service is coded or where the service is hosted. The message format is XML.
• Web Services Description Language (WSDL) is an XML-based interface and interface description language. The service provider uses a WSDL document in order to specify the operations a Web service provides, the parameters and data types of these operations and the location and transport bindings to be used to access the service.
• Web Services Inspection Language (WSIL) is an XML-based specification about how to locate Web services without the necessity of using UDDI. However, WSIL can be also used together with UDDI, that is, it is orthogonal to UDDI and does not replace it.
• Universal Description, Discovery, and Integration (UDDI) is both a client-side API and a SOAP-based server implementation that can be used to store and retrieve information on service providers and Web services.
• The evolution and wide acceptance of Web services on the back of the Internet has taken Enterprise Application Integration to a new level. It has led to new architectures like service-oriented architecture (SOA) and patterns like Enterprise Service Bus (ESB). These have helped to overcome some of the practical problems associated with using Web services. We discuss SOA and ESB in more detail in the next subsection.