DevChannel.org
Title
DevChannel: Resources for Enterprise Developers
Description
A Document Type Definition (DTD) is an optional part of an XML document that defines the document's exact layout and structure. Although they're not essential, there are several advantages to using DTDs, and these advantages become more obvious as the size and complexity of the XML code increases. Most non-trivial applications of XML benefit from a DTD, so most document authors need to know how to write them, and most software developers working with XML need to know how to take advantage of them.
While there are many different implementations of the Simple Object Access Protocol (SOAP), powers Web services, there is one commonality among them all: They all have a Web service Description Language interface. WSDL is an XML document format that contains a complete specification, a sort of blueprint, of a Web service. It contains everything needed to make requests to Web services, such as operation names, their input and output parameters, and their schema types.
An application developer can choose any one of a number of strategies to read and use an XML document. In some very simple examples a script containing a number of regular expressions might do the job, but normally a more rigorous technique is required. The Simple API for XML (SAX) is one of the two key techniques for analysing and processing XML documents (the other is the more complicated Document Object Model (DOM)).
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