The following topics introduce basic XQuery concepts and
describe how XQuery works with a DB2® database.
Introduction to XQuery XQuery is a functional programming language that was
designed by the World Wide Web Consortium (W3C) to meet specific requirements
for querying and modifying XML data.
Comparison of XQuery to SQL
DB2 databases support
storing well-formed XML data in a column of a table and retrieving
the XML data from the database by using SQL, XQuery, or a combination
of SQL and XQuery. Both languages are supported as primary query languages,
and both languages provide functions for invoking the other language.
Retrieving DB2 data with XQuery functions
In XQuery, a query can call one of the following functions
to obtain input XML data from a DB2 database: db2-fn:sqlquery and db2-fn:xmlcolumn.
XQuery and XPath data model
XQuery expressions operate on instances of the XQuery and XPath
data model (XDM) and return instances of the data model. The XDM provides
an abstract representation of one or more XML documents or fragments. The
data model defines all permissible values of expressions in XQuery, including
values that are used during intermediate calculations.
Serialization of the XDM
The result of an XQuery expression, which is an instance
of the XDM, can be transformed into an XML representation through
a process called serialization.
XML namespaces and QNames
XML namespaces prevent naming collisions. An XML namespace is
a collection of names that is identified by a namespace URI. Namespaces provide
a way of qualifying names that are used for elements, attributes, data types,
and functions in XQuery. A name that is qualified with a namespace prefix
is a qualified name (QName).
Language conventions
XQuery language conventions are described in the following topics.
DB2 Version 9.7 for Linux, UNIX, and Windows