XQuery Reference Guide
This chapter describes the version of the XQuery specification implemented in BEA Liquid Data for WebLogic. It also briefly describes the XQuery specification and provides links to more information about XQuery.
For a list and the syntax of the functions and operators implemented in Liquid Data, see Functions Reference.
XML is evolving from a W3C specification for a markup language to an entire family of specifications and technologies. The W3C has chartered working groups focused on creating, among other things, specifications for schemas and a query language. The evolving query language is XQuery, which gives XML developers a structured solution for accessing and querying XML data. The W3C Query Working Group used a formal approach by defining a data model as the basis for XQuery. XQuery uses a simple type system and supports query optimization. It is statically typed, which supports compile-time type checking.
Whereas SQL is a well-known query language for querying relational databases, XQuery is a query language for querying XML-based information. Developers who are familiar with SQL will find XQuery to be a natural next step.
However, unlike SQL, which always returns two-dimensional result sets (rows and columns), XQuery results can conform to a complex XML schema. The XML schema can represent a hierarchy of nested elements that represent very detailed and complicated business data and information.
For information about the syntax of XQuery in Liquid Data, see Understanding XQuery in Liquid Data.
Liquid Data models various types of data sources as XML schemas. You can combine elements and attributes of the schemas in a query written in the XQuery language. The Liquid Data Server then executes the query and returns the results.
Once you have configured Liquid Data access to the data sources you want to use (relational databases, Web Services, application views, data views, and so on), you can query the data by issuing queries written in XQuery to Liquid Data, and the Liquid Data Server will fetch the data from the underlying data sources and return the query results.
The Data View Builder provided with Liquid Data is a tool that generates queries in the XQuery language. You can combine data from multiple sources by dragging-and-dropping the XML schemas and a full complement of functions to generate queries in XQuery. The Data View Builder also allows you to test, save, and deploy queries. For details on the Data View Builder, see Building Queries and Data Views.
You can learn more about XML schemas on the W3C Web site at http://www.w3.org/XML/Schema and http://www.w3.org/2001/12/xmlbp/xml-schema-wg-charter.html.
You can learn more about the standard on the W3C Web site at http://www.w3.org/TR/xquery/.
For a comprehensive list of relevant XQuery references, see XQuery Links in the Liquid Data Product Overview.
For the syntax of XQuery in Liquid Data, see Understanding XQuery in Liquid Data.