The Web Server Environment - Database Processing: Fundamentals, Design, and Implementation - page 521

Standard Description

XML Extensible Markup Language. A document markup language

that started the following:

XSL XSLT Stylesheet. The document that provides the {match,

action} pairs and other data for XSLT to use when transforming
an XML document.

XSLT A program (or process) that applies XSLT Stylesheets to an XML

document to produce a transformed XML document.

XML Schema An XML-compliant language for constraining the structure of an

XML document. Extends and replaces DTDs. Under
development and very important to database processing.

XPath A sublanguage within XSLT that is used to identify parts of an

XML document to be transformed. Can also be used for
calculations and string manipulation. Comingled with XSLT.

XPointer A standard for linking one document to another. XPath has

many elements from XPointer.

SAX Simple API (application program interface) for XML. An event-

based parser that notifies a program when the elements of an
XML document have been encountered during document
parsing.

DOM Document Object Model. An API that represents an XML

document as a tree. Each node of the tree represents a piece of
the XML document. A program can directly access and
manipulate a node of the DOM representation.

XQuery A standard for expressing database queries as XML documents.

The structure of the query uses XPath facilities, and the result of
the query is represented in an XML format. Under development
and likely to be important in the future.

XML
Namespaces

A standard for allocating terminology to defined collections.
X:Name is interpreted as the element Name as defined in
namespace X. Y:Name is interpreted as the element Name as
defined in namespace Y. Useful for disambiguating terms.

Figure 11-63
Important XML Standards

XQuery is the W3C standard for querying XML documents. You can think of it as SQL for
XML documents. Visit www.w3.org/standards/xml/query for more information on XQuery.
The last XML standard we will mention, XML Namespaces, is very important because it is
used to combine different vocabularies into the same XML Schema. It can be used to define and
support domains and to disambiguate terms. The need for the latter occurs when a document
contains synonyms. For example, consider a document that has two different uses for the term
Instrument . Suppose that one use of this term refers to musical instruments and has the subele-
ments {Manufacturer, Model, Material}, as in {Horner, Bflat Clarinet, Wood}, and a second use
of this term refers to electronic instruments and has the subelements {Manufacturer, Model,
Voltage}, as in {RadioShack, Ohm-meter, 12-volt}. The author of the XML Schema for such a docu-
ment can define two different namespaces that each contains one of these definitions. Then the
complexType definition for each of these definitions of Instrument can be prefixed by the label of
the namespace, as was done in our schema documents when we used the label xsd. There is more
to XML Namespaces, and you will undoubtedly learn more as you work with XML.
The XML Standards Committee continues its important work, and more standards will
be developed as the needs arise. At present, work is under way for developing security stan-
dards. Keep checking www.w3.org f or more information.