Page 23 - GAO-02-327 Electronic Government: Challenges to Effective Adoption of the Extensible Markup Language

Chapter 1: Background: Features and Current
Federal Use of XML

document. XSL-FO provides the formatting vocabulary to carry out such a
transformation.
• The XML Schema standard provides a superset of the capabilities found in
XML 1.0 for document type definitions (DTDs). It offers comprehensive
instructions for describing the structure and constraining the contents of
XML documents. The XML Schema standard also specifies a robust system
of data types, including a number of predefined data types that can be
associated with XML data elements and attributes to help manage dates,
numbers, and other special forms of information.
• The XML Namespace standard provides guidelines for uniquely identifying
the data definitions that appear in an XML document, thus avoiding
ambiguity among data elements with the same name that may come from
different sources.

In addition to these core standards, a number of supplemental standards
have been developed or are proposed to codify how additional functions
should be performed. When developers identify a need for new functions
to be incorporated into XML technology, new supplemental specifications
can be developed as extensions to the core XML standards. These
supplemental specifications have been designed as separate standards so
that they can be used when needed as modular enhancements to
individual implementations. Examples of supplemental technical
standards include the following:

• The Document Object Model (DOM) is a platform-independent and
language-neutral application-programming interface. DOM allows
programmers to develop applications that can dynamically access and
update the content and structure of XML documents.
• The XML Linking Language (XLink) standard allows XML documents to
contain links similar to HTML hyperlinks. While XLink is similar to HTML
linking, it adds new features to make links more flexible and precise. For
example, XLink allows a link to point to a specific reference within an
external file rather than simply pointing to the file as a whole, as in HTML.
• XML Path Language (XPath) provides a common syntax and semantics for
addressing specific parts of an XML document. XPath gets its name
through its use of a path notation for navigating through the hierarchical
structure of an XML document.

XML Was Designed to An important advantage of XML is that it is flexible enough to
accommodate an unlimited number of uses. Each new use is
Accommodate accommodated by the development and standardization of extensions to
Numerous Extensions the core set of XML standards. This is what makes XML “extensible”; its
structure can be adapted (or extended) to meet many different needs.

Page 19 GAO-02-327 Electronic Government