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Building Queries and Data Views

W3C XQuery, XML, and Liquid Data

XQuery is a World Wide Web consortium (W3C) standard XML-based Query language. 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. Liquid Data uses XQuery to query multiple types of data sources—the structure of which are represented as XML by the query engine.

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, a more approachable XML language for database developers, including the published specifications for schemas and a query language. The evolving language is XQuery, which gives XML developers a structured solution for accessing XML data. The W3C Query Working Group used a formal approach by defining a data model and formal query algebra 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. It includes familiar database operations such as projection, iteration, selection, and join.

XQuery Use in Liquid Data and Data View Builder

BEA Liquid Data uses a stable components of the W3C XQuery specification to take advantage of XML query power as the standards continue to evolve. By using XQuery, Liquid Data can model XML schemas for various types of data sources. These schemas are surfaced as design tools in the Data View Builder, which generates queries in XQuery in the background. The Liquid Data server can process ad hoc or Builder-generated queries in XQuery syntax and use them to query all different kinds of data sources (relational databases, Web services, application views, data views, and so on) and return results in XML.

Once you have configured Liquid Data access to the data sources you want to use (see the Liquid Data Administration Guide), you can query the data by sending queries written in XQuery to the data sources via Liquid Data.

The Role of XML in Creating Global Business Solutions

By supporting XML technology, creating specifications, fostering software development, the W3C hopes to use XML as a forum for information exchange, business development, and global communication.

XML is being used on the Internet is to create a simple way to exchange data among diverse clients. Proprietary data definitions and access methods inhibit data exchange. They lock you into using only those products and programs that can send, receive, and process your data.

You could compare the universality of XML to a global monetary exchange standard, or to an international spoken language that removes barriers to global commerce and communication. Data View Builder and the Liquid Data query generation engine adhere to these standards to facilitate cross-platform and cross-repository access to critical business information.

You can learn more about XML on the W3C Web site at http://www.w3.org/XML/.

Supported XML Schema Versions In Liquid Data

XML schemas are used in Liquid Data to describe the hierarchical structure of the various data sets with which you are working. Liquid Data recognizes XML Schema versions 2001, 2000/08, and 2000/10.

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.

For an introduction on working with schemas in the Data View Builder see Source and Target Schemas.

Learning More About the XQuery Language

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 the topic XQuery Links in "Liquid Data Concepts" in the Liquid Data Product Overview.