Summary: A current hot topic on the web right now are Web Services. This short guide will allow you to learn more about web services.
Web services are not really anything that new, and actually, if you've ever used an RSS or Atom feed to pull news from a website, you have an idea of how a web service might work.
Web services exchange data from a server to a client, using an XML format to send requests, so both the server and the client can understand each other. (XML Introduction).
A better way to understand a web service is to compare it to a HTML form communication with a server side script (such as PHP or ASP) to post and send data. Both web services and forms send and receive requests. The only major difference is that a web service uses XML.
Examples of Web Services In Action
As said before, RSS and Atom feeds are a simple example of how a web service works, most commonly, XML-RPC or SOAP are also used to communicate between a server and a client.
XML-RPC is a type of web service and has been around since 1998, though not an official W3C standard, it is widely used. XML-RPC was developed by Useful Inc, along with Microsoft.
SOAP, a web service, is listed as a W3C standard, and is similar in ways to XML-RPC. SOAP also has backing from IBM, as well as Microsoft.
SOAP or XML-RPC?
Briefly, SOAP was intended to fill gaps in XML-RPC. An example is, it is easier to send a multi-dimensional array with SOAP rather then with XML-RPC. SOAP also has more features then XML-RPC, but XML-RPC on its own, has its uses.