Contracts and types

Web services are gaining momentum as a platform, both conceptual and technological, upon which to develop applications that take advantage of the Internet infrastructure. The popularity of standards and proposed standards like XML, WSDL [4], WS-ReliableMessaging [2], WS-Security [2], BEPL4WS [5], WSCI [1], and others lend credence to this claim. Much to their credit, these and other standards have led to the development of a basic substrate of tools for wiring together the nodes of a dis-tributed application. For example, Microsoft’s.Net offering provides support for XML and WSDL, and its WSE 1.0 supports many WS-* standards and proposals. On the other hand, by and large, these stan-dards say little about the correct functioning o