XML programming

XML and XSL

XML (Extensible Markup language) is a subset of SGML which was designed to be fully compatible with SGML. XML is not really a programming language, but a standard for creating languages which meet the XML criteria. It describes a syntax which you use to create your own language. You create your own data names with opening and closing tags to categorize data.

XSL are XML style sheets to display the data. One style sheet could be created to display data on several web pages with a consistent layout. This makes design changes much easier to accomplish. XML is great for online catalogs and storing data without needing databases.

XML can be written in any language: English, Chinese, French, Spanish, or any other language. A program called a parser will read the XML syntax and get the information for you. Because not all browsers include the necessary parser to interpret XML, programmers often run the XML and XSL scripts through the parser on their computers and upload the generated HTML documents to the web server for you. You will never see the XML and XSL pages in this case.

There are numerous industry-standard vocabularies to describe various types of data. Scalable Vector Graphics (SVG) is an XML vocabulary for describing two-dimensional graphics. MathML is an XML vocabulary for describing mathematics as a basis for machine to machine communication. Chemical Markup language (CML) is an XML vocabulary for the management of chemical information. There are many more.

The DOM (Document Object Model) provides a means for working with XML documents (and other types of documents) through the use of code, and a way to interface with that code in the programs we write. It uses a lot of memory, uses nodes to find things, uses properties and methods, object (elements) for dynamic web pages. It follows the hierarchy (family tree) to get to the data. Think flow charts.

XHTML is HTML that follows XML standards. All tags are lowercase and have closing tags. XML-related resources:

Ron Bourret's XML Links includes sites in English and German.
XDBM is an embedded database designed specifically to handle XML data. This open source project was written in C programming language for Microsoft or POSIX operating systems.
eXist is an Open Source native XML database featuring pluggable storage backends, efficient, index-based XPath query processing, extensions for keyword search and tight integration with existing XML development tools. The database is lightweight, completely written in Java and may be easily deployed in a number of ways, running either as a stand-alone server process, inside a servlet-engine or directly embedded into an application.
XML and Web Services Magazine for more info