Web Services Overview

The Internet today has many different technologies and protocols for moving information from one place to another and enabling communication between systems. As time passes, it seems that the number of new ways to perform these functions increases as companies innovate and add proprietary standards into their infrastructures. Although innovation is great and growth is welcome, the expense associated with all these systems and standards increases also.

The cost of Enterprise Application Integration (EAI) is huge and increases every year as businesses merge and information systems must integrate. It is easy to use terms such as CORBA, RMI, EDI, TCP/IP, HTTP, and so on as the list grows and complexity increases. There is no telling which companies will merge or be bought out by others tomorrow, requiring expensive information systems integration. To manage the complexity and reduce the costs, businesses need a way to manage their EAI requirements in an efficient manner.

The .NET solution to this problem is Web services: reusable APIs that enable computer systems to interoperate. They are based on open standards that make them platform- and language-independent. These open standards are independent of transport layer protocols. Web Service messages are transported in an XML-based SOAP envelope.

Although most Web services use HTTP for a transport layer, the formal specification is written so that other transports, such as SMTP, may be used also. Web services package messages into SOAP envelopes, which is a standard XML format for Web Services communications.

WHAT DOES SOAP MEAN?

SOAP originally was an acronym for "Simple Object Access Protocol." However, the words don't accurately reflect what Web services are, so the latest standards simply use SOAP as a term that stands on its own. Most notably, SOAP is not object-oriented it is a message-passing protocol.

Normally, a client connecting to a Web service knows which Web service it will be using and adds a URL to a configuration file that the application picks up at runtime. Another open standard, Universal Description Discovery and Integration (UDDI), is a directory service that helps find and identify available Web services.

Applications that want to communicate with Web services must have some way of knowing what interface a Web service exposes. The Web Service Description Language (WSDL) is an XML document that describes the messages a Web service may accept and how to connect with the Web service.