XML eXplained

XML has generated acronyms to well beyond the point of confusion. Here are the key terms, in alphabetical order:

CDATA: A section of an XML document, delimited by CDATA markers, that contains raw character data. Characters that would otherwise be interpreted as tags or other XML metadata can be included in a CDATA section, where they are treated as ordinary characters without any special meaning.

DOM: Document Object Model. This is a way of representing an XML document as a hierarchy of objects that can be manipulated programmatically.

DTD: Document Type Definition. A document which defines elements, attributes and other constraints so that XML documents of the specified type can be validated. An alternative to DTDs are XML Schema.

Namespace: A means of resolving naming conflicts by defining a globally unique name for a particular set of elements. In an XML document, you can tell which namespace an element belongs too either by checking its prefix, or by looking for the default namespace. Namespace prefixes are defined with the xmlns attribute.

RSS: An XML document that wraps a collection of web links in metadata that defines properties such as title, description, creator, date, and rights. RSS documents are used for newsfeeds and for weblogs ("blogs"). As to what the letters stand for, that is contentious. They might stand for RDF Site Summary, or possibly Really Simple Syndication. These indicate the two streams of RSS development, with each side adopting a different interpretation.

SAX: Simple API For XML. Originally a JAVA API for parsing XML. It works by raising events as each significant item in the document being parsed.

SMIL: Synchronized Multimedia Integration Language. An XML application for multimedia and animation.

SOAP:Simple Object Access Protocol. An XML protocol for doing application messaging and remote procedure calls over the internet.

SVG: Scalable Vector Graphics. An XML application for defining vector graphics. In theory SVG is the official web standard for vector graphics, but Macromedia’s proprietary and non-XML Flash is the current real-world standard.

UDDI: Universal Description, Discovery and Integration. A public registry that enables businesses to publish information about the web services they offer. UDDI offers a programmatic interface as well as a user interface.

Web Service: An application accessible over the Internet through an XML interface.

WSDL: Web Service Description Language. An XML format for describing XML web services, including the type definitions, messages and actions used by that service. The WSDL document should tell applications all they need to know to invoke a particular web service.

XDR: XML Data Reduced: an early version of XML Schema, developed by Microsoft and still used by some Microsoft products. Uses the file extension .xdr.

XHTML: Extensible HTML, a reformulation of HTML as a validated XML.application.

XML: Extensible Markup Language, a specification for defining mark-up languages.

XML-RPC: XML Remote Procedure Call, an older alternative to SOAP that has the advantage of being a simpler, settled standard.

XML Schema: An XML format for constraining and validating XML documents and defining data types.

XSD: XML Schema Definition. A document containing an XML Schema, with an .xsd extension.

XSLT: Extensible StyleSheet Language Transformations. An XML application that defines rules by which an XML document can be transformed into another type of document, which might or might not be XML.

XLINK: XML Linking, or hyperlinks on steroids. An attribute-based language for linking a resource to one or more other resources, with extended information about what type of link it is and how it should be rendered. Links may be bidirectional, and can be defined outside the documents they link.

XPATH: A non-XML language for identifying specific parts of an XML document. This is not just for use in navigation, but also in querying and transforming XML. XPATH expressions are frequently used in XSLT.

XPOINTER: A non-XML language for referencing a point or a range within an XML document. Builds on XPATH.

XQUERY: XML Query Language. Work in progress to define a language for querying one or more XML documents, a sort of XML equivalent to SQL (Structured Query Language). XPATH, XPOINTER, XQUERY and XSLT have considerable overlap, a fact which is recognized by the various working groups.

Continue to part 4: resources

Copyright Tim Anderson January 2004. All rights reserved.
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