Don't let all the buzz about "web services" fool you; the basic idea of a web service is very simple. It is simply a matter of providing data in response to a request using standard web transport protocols (i.e. HTTP / HTTPS). Everything else (XML, SOAP, WSDL, etc.) is just a layered technology that allows you to extend the basic functionality of the service. REST-based services are basically the simplest simple services you can create — they are built on the basic HTTP / S protocol and not much more.
The main difference between a service and a traditional website is that the service is data-oriented, not presentation-oriented; that is, services are usually not related to how the data is formatted and displayed (it depends on the client), but rather what data is returned. So ... are you delivering XML data via HTTP? Check it out. You have a service. Congratulations!
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