Database Reference
In-Depth Information
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 the semantics of a vocabulary. XML Schema Definition
(XSD) is the language for defining XML vocabularies.
The World Wide Web Consortium (W3C) developed XML in 1996. Intended to support 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 provides 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 documents into other XML documents.
Why XML
XML is a multipurpose, extensible data representation technology. XML increases the possibilities for
applications to consume and manipulate data. XML is different from the relational data; XML data can
be structured, semistructured, or unstructured. XML support in SQL Server 2012 is fully integrated with
the relational engine and query optimizer, allowing you to retrieve and modify XML data and even
convert 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:
•
Since XML is self-describing, applications can consume XML data without
knowing the schema or structure. XML data is always arranged hierarchically in a
tree structure. The XML tree structure must always have a root, or parent node,
which is known as the XML
document
.
•
XML maintains document ordering. Because XML is arranged in a tree structure,
maintaining node order becomes easy.
•
XML Schema is used to define valid XML document structure.
•
Because of XML's hierarchical structure, you can search inside the tree structures.
XQuery and XPath are the query languages designed to search XML data.
•
Data stored as XML is extensible. It is easy to manipulate XML data by inserting,
modifying, and deleting nodes.
