Web Service

Web Service Technologies and Protocols

Web services rely on a low-level Web communication protocol, Hypertext Transfer Protocol (HTTP), and a group of high-level communication standards that describe the syntax and semantics of software communication, including Simple Object Access Protocol (SOAP); Web Service Description Language (WSDL); and Universal Description, Discovery, and Integration (UDDI). Software developers can use these protocols and languages to create Web services. SOAP is an XML-based protocol (built on the top of HTTP) to describe semantics for the data exchange and access functions in a distributed network environment. UDDI is an XML-based registry to help search and discovery Web services cross the network. A UDDI node (a server) will accept the submission of Web service metadata (WSDL documents) from Web service providers and populate the registry to facilitate future search and access of Web services. WSDL is used for describing the capabilities/functions of a Web service, and a WSDL document is actually a metadata file for Web services. In addition, there are other complementary specifications for Web services, such as WS-Security (for network security), WS-ReliableMessaging (for messaging reliability), and BPEL4WS (for business process).

An important concept in the development of Web services is the service-oriented architecture (SOA). SOA can allow multiple applications running on heterogeneous platforms to be connected to each other and create a chain of Web services for different users and applications. For example, a bank customer can ask his or her online banking Web service to pay electric and gas bills automatically every month (chaining an online banking service with a billing service from an energy company). There are three major components [Page 514]in SOA: service providers, service consumers, and service registry agents. Service providers create Web services for potential customers (or users). Service consumers search and utilize Web services for their own needs. Service registry agents are information brokers who can provide the linkage between the service providers and the service consumers. Registry agents will tell the consumers where to find the Web services they requested and also help the service providers publish and advertise their Web services.

Interoperability and openness are the two key advantages for the development of Web services. The openness of Web services specifications encourages software developers to create flexible and customizable Web applications based on Web services standards. Interoperable Web services can allow end users or service consumers to combine multiple functions and operations into a single Web document for their own needs. Some commonly used object programming languages in developing Web service applications are C++, C#, and Java.

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