A few years ago Web services were not fast enough to be interesting.
When all major platforms could access the Web using Web browsers, different platforms couldn't interact. For these platforms to work together, Web-applications were developed.
Web-applications are simply applications that run on the web. These are built around the Web browser standards and can be used by any browser on any platform.
By using Web services, your application can publish its function or message to the rest of the world.
Web services use XML to code and to decode data, and SOAP to transport it (using open protocols).
With Web services, your accounting department's Win 2k server's billing system can connect with your IT supplier's UNIX server.
There are things 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.
Connect existing software.
Web services can help to solve the interoperability problem by giving different applications a way to link their data.
With Web services you can exchange data between different applications and different platforms.
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