Using XML - Beginning C# 2008 Databases: From Novice to Professional - page 119

n Note In essence, each XML document is an instance of a language defined by the XML elements used
in the document. The specific language may or may not have been explicitly defined, but professional use of
XML demands carefully planning one's XML vocabulary and specifying its definition in a schema that can be
used to validate that documents adhere to both the syntax and semantics of a vocabulary. The XML Schema
Definition language (usually referred to as XSD) is the language for defining XML vocabularies.
The World Wide Web Consortium (W3C) developed XML in 1996. Intended to sup-
port a wide variety of applications, XML was used by the W3C to create eXtensible HTML
(XHTML), an XML vocabulary. Since 1996, the W3C has developed a variety of other
XML-oriented technologies, including eXtensible Stylesheet Language (XSL), which pro-
vides the same kind of facility for XHTML that Cascading Style Sheets (CSS) does for
HTML, and XSL Transformations (XSLT), which is a language for transforming XML doc-
uments into other XML documents.
Why XML?
XML is multipurpose, extensible data representation technology. XML increases the pos-
sibilities for applications to consume and manipulate data. XML data is different from
relational data in that it can be structured, semistructured, or unstructured. XML support
in SQL Server 2005 is fully integrated with the relational engine and query optimizer,
allowing the retrieval and modification of XML data and even the conversion between
XML and relational data representations.
Benefits of Storing Data As XML
XML is a platform-independent, data-representation format that offers certain benefits
over a relational format for specific data representation requirements.
Storing data as XML offers many benefits, such as the following:
• Since XML is self-describing, applications can consume XML data without know-
ing the schema or structure. XML data is always arranged hierarchically in a tree
structure form. XML tree structure must always have a root, or parent node, which
is known as an XML document .
• XML maintains document ordering. Because XML is arranged in tree structure,
maintaining node order becomes easy.
• XML Schema is used to define valid XML document structure.