Section 6.1. Role of WSDL in WS-SOA

6.1. Role of WSDL in WS-*/SOA

WSDL is the foundation of a set of specifications in the area of describing a servicethat is, for capturing service metadata. As such, WSDL plays a critical role in enabling many of the advantages of Web services and service orientation, such as loose coupling and future proofing. In particular, designing systems around service contracts as defined by WSDL gives those systems flexibility to apply late or dynamic binding and overall looser coupling.

WSDL is used in Web services in two distinct scenarios:

• Describing a service for its clients In this case, the WSDL document describes a published service for its clients. The description contains message declarations, operation or message exchange declarations, and the location of a service that processes those messages, in addition to mechanisms for interacting with that service. The primary purpose of WSDL in this scenario is to enable a client of that service to use that service effectively.

• Describing a standard service for service implementors In this case, the WSDL documents a standard service. An example is a vertical market segment, such as manufacturers of automotive tires, getting together and agreeing on what the tire-buying service that is offered to car manufacturers looks like. After the message formats and the interactions involved with tire buying have been agreed to by the tire manufacturers, a WSDL document describes them. Then a specific tire manufacturer can start with that WSDL and offer the service, which results in another WSDL. This other WSDL plays the role of a WSDL from the previous scenario: Its clients (automotive manufacturers) can use it.