Web Services Made Easy With Delphi

SOAP is a protocol that enables applications to send messages to each other without the hassle of having to worry about interoperability or firewall access. Interoperability in this case means that you should not have to worry or even know about what platform a service is running on or its implementation, if and when you want to use it. A comparable protocol and by far the most popular in use today is HTTP. We use this protocol to access web pages or to surf the net. HTTP ensures that you do not have to worry about what kind of server (Windows, UNIX, etc.) serves you the pages you are viewing or if the pages that you are viewing are made available by a PHP or ASP script.

Can you imagine the inconvenience if you had to use a different web browser for each type of web page that you wanted to visit? All that you need to know to view a website is its URL. In a similar manner, SOAP takes care of those problems for applications that communicate across networks such as the Internet.

All that you need to know to use a web service are its methods and the parameters that it requires. Then you need a client program to access the "services." Firewalls should not be a problem if the client program is configured correctly.

To summarize:

• SOAP is used to transfer messages between applications. It puts the message in a SOAP "envelope" tag like so: <SOAP-ENV:Env,elope      xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">
  </SOAP-ENV:Envelope>

• SOAP takes care of interoperability and security when applications exchange data.

Say you've found a web service on the Internet. How would you know what methods are available and how to use them? This is where WSDL comes in.