With the term "big" web services [1,2] we refer to web services that are implemented using technologies like XML [3], WSDL [4] and SOAP [5]. This kind of web services does not follow the REST architectural style and rather proposes a distributed computing paradigm that is inspired by more traditional technologies, such as CORBA or DCOM, that follow an object-oriented implementation style, however with message exchanges at runtime. WSDL/SOAP web services can be complex beasts that may maintain internal state and may require the client to follow a pre-defined order of interaction (a so-called protocol). They may also come with a set of advanced features, such as transactions, usage policies, service level agreements, security, etc., that are typically not supported by state-of-the-art RESTful web services.
This style of web services is important for the development of distributed, mission-critical and enterprise-level applications.
In order to enable developers to discover a given web service, it is important that the existence of this web services is known to the developers. For this to happen, it is typically not enough to deploy a web service on a web server. It is important to properly document, i.e., describe the service, so that others can search for descriptions, inspect them, and understand how to interact with the service [1]. In this context of "big" web services, the Web Services Description Language (WSDL [2]) is used for this purpose. The language targets both machines and humans, the former to enable the automation of repetitive programming tasks, the latter to enable understanding the service.
Learn here how to describe your own services and how to make good use of service descriptions.
Here you can download the slides of the lesson:
Introduction to SOAP/WSDL Web Services
An example of SOAP/WSDL Web Service
Draft of WSDL file for the previous SOAP/WSDL Web Service example: wsdl
Test here your comprehension and preparation.