Like Hypertext Markup Language (HTML), XML is a markup language and a subset of Standardized General Markup Language (SGML). XML, however, is more complete and disciplined, and it allows you to define your own application-oriented markup tags. These properties make XML particularly suitable for data interchange.

You can generate XML-formatted documents from data stored in Adaptive Server and, conversely, store XML documents and data extracted from them in Adaptive Server. You can also use Adaptive Server to search XML documents stored on the Web.

Adaptive Server uses the XML Query Language (XQL) to search XML documents. XQL is a path-based query language that searches the XML documents using the XML structure.

Many of the XML tools needed to generate and process XML documents are written in Java. Java in Adaptive Server provides a good base for XML-SQL applications using both general and application-specific tools.

The XQL processor is a Java ficility that is included with the Adaptive Server. It allows you to query and access XML data stored in Adaptive Server, and to display the result set as XML documents. See Chapter 7, “Selecting Data with XQL.”