What is XML?

XML stands for Extensible Markup Language. XML provides a structured way to define data in plain text format, so that data can be exchanged between computers. SOAP messages are XML documents, which are just text files formatted according to some very specific guidelines. (SOAP is the specification that defines the guidelines used to describe remote procedure calls using XML.) XML provides the syntax needed to define a markup vocabulary—the tags and attributes needed to describe a particular type of data. XML files can be created using a simple text editor, such as Notepad. XML is more flexible than comma-delimited or fixed-length formats, since XML encloses information inside descriptive tags in a tree-based hierarchy. Before a SOAP request can be transported to another computer, the request is structured using XML so that the remote system can interpret the request in accordance with the SOAP specification. Responses from the remote procedure are returned as XML documents.

SOAP uses XML to package the data passed to a method, or received as a response. SOAP itself is nothing more than a set of rules that define how to describe method calls and return values using XML syntax. XML merely describes data, without consideration for the way that the data is processed or presented.

To summarize, SOAP defines conventions needed to invoke the methods of a web service. SOAP tools on CIC allow web services to be created using Interaction Designer. SOAP uses existing transport protocols (such as HTTP) to transmit an XML payload to another computer. The payload contains everything that the remote computer needs to execute a function (arguments and data). Services that understand SOAP requests can be expected to return XML responses in accordance with the rules of SOAP. The relationship between SOAP and XML can be expressed this way:

SOAP documents are XML documents that conform to a particular specification, allowing the exchange of messages. Therefore, to understand SOAP, you need a working knowledge of XML.