Interoperability has highest priority.
When all major platforms could access the Web using Web browsers, different platforms could interact. For these platforms to work together, Web applications were developed.
Web applications are simple applications run on the web. These are built around the Web browser standards and can mostly be used by any browser on any platform.
Web services take Web applications to the next level.
Using Web services your application can publish its function or message to the rest of the world.
Web services uses XML to code and decode your data and SOAP to transport it using open protocols.
With Web services your accounting departments Win 2k servers billing system can connect with your IT suppliers UNIX server.
Web services have two types of uses.
Reusable application components
There are things different applications need very often. So why make these over and over again?
Web services can offer application components like currency conversion, weather reports or even language translation as services.
Ideally, there will only be one type of each application component, and anyone can use it in their application.
Connect existing software
Web services help solve the interoperability problem by giving different applications a way to link their data.
Using Web services you can exchange data between different applications and different platforms.