XML: Structuring Data for the Web: An Introduction
May 3rd 1998
The XML Specifications
Note: If you are unfamiliar with the meaning of the W3C terms
"Recommendation", "Proposed Recommendation",
"Working Draft", and "Note", refer to the
World Wide Web
Consortium Process pages, especially the
Documents
section.
The 250+ member
World Wide Web Consortium
approved the
XML 1.0 Specification
as a W3C Recommendation on February 10, 1998. However, the W3C XML
efforts began in July 1996 when the SGML Editorial Review Board became
the XML Working Group, eventually producing the first XML draft in
November 1996. (These and other events are detailed in the W3C's
Timeline: Events and
Publications, as well as in the author's
Timeline
of XML Events.)
It's important to understand that XML is really a collection of
emerging specifications and related "vocabularies" based
upon the XML syntax. Formally, XML is actually three specifications
(or four depending on where you draw the line), each presently at a
different level of maturity (listed in order of most mature to least
mature):
- XML 1.0 Recommendation -
this is the Extensible Markup Language
specification
which explains the syntax of the meta language in great detail;
- XML Linking Language
(XLink) and
XPointer - these two
related W3C Working Drafts describe numerous ways to express complex
but flexible linking relationships between documents (and sections);
and
- Extensible Style Language
(XSL)
- currently still a W3C Note, XSL describes how XML may be rendered
using different style sheets, perhaps targeted for different devices.
As you might imagine, the specifications are a bit difficult to
understand, so I'd recommend instead consulting
The Annotated XML
Specification by Tim Bray (one of the XML specification's
authors from
Textuality
and also a Netscape consultant).
Several other specifications are related to the overall
XML activities
of the W3C. The
Document Object Model
Specification (fourth Working Draft, dated 4/16/98), which
describes "a platform- and language-neutral interface that will
allow programs and scripts to dynamically access and update the
content, structure and style of [HTML and XML] documents",
contains a large
section
devoted to XML. Another related Working Draft is
Namespaces in XML,
which introduces the notion of qualified names to prevent potential
conflicts between identically named XML elements by associating a
prefix which identifies an intended namespace with an URI.
Resource Description
Framework (RDF) is the Working Draft that describes a language
for writing metadata. The W3C Note simply called
XML-Data
submitted by Microsoft, ArborText, DataChannel and Inso Corp.. is a
proposal to make XML database-ready, especially for three-tier
architectures and heterogeneous databases. They introduce a suggested
syntax for schemas and a model for extending XML elements (by adding
data types, presentation rules, inheritance, etc.). [As a W3C Note, XML- Data is not yet officially endorsed by the World Wide Web
Consortium.]
See also the discussion of
Emerging XML Vocabularies
for additional related documents. A subsequent WDVL article will
cover XML syntax in detail.
XML: Structuring Data for the Web: An Introduction
XML: Structuring Data for the Web: An Introduction
XML: Structuring Data for the Web: An Introduction
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