Databases Get Better At Managing XML Data

The explosive growth of XML data on the Web has pushed large database vendors and standards organizations into action.
The Web supports a massive amount of content formatted in XML, the standard method for structuring online documents and data. Relational databases, however, have had a hard time handling XML documents, which are structured as a hierarchy--a set of nodes, stored in sequence--and don't fit the rows-and-columns tabular format used by those databases.

That's starting to change. Oracle 10g, Microsoft SQL Server 2005, and IBM's DB2 9.0, released last week, include XML handling capabilities, an important step in making XML queries easier. Database users can further benefit from XQuery, an XML data-access language and emerging standard.

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The updated SQL/XML standard will simplify:
Retrieval of XMLcontent from relational databases using SQL and XQuery
Storage of XMLdocuments in relational databases, by putting content into SQL-accessible tables
Publication of XMLdocuments built from results of both XQuery and SQL queries

These developments are important for businesses looking to include dissimilar types of information in a database. Beth Israel Deaconess Medical Center in Boston uses InterSystems' hybrid object/relational database system, Cache, for its CareWeb system used by doctors. Charts, images, subtle relationships between medicines, allergies, and reports on a patient's vital signs from operating room to recovery all can be represented in CareWeb, while older relational systems would be too slow to build screens of such dissimilar types of data. Growing support for XML in standard databases eventually may eliminate the need for a specialized one, says Robert Beckley, Beth Israel's director of information systems. The hospital already provides content to public health officials in XML. "Someday, all that CareWeb data could be XML," he says.

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Some businesses have been storing XML data in the form of messages and documents in specialized XML systems, such as Software AG's Tamino and Ipedo's Ipedo XIP. These systems break content into a sequence of nodes that can be tagged, then invoked to retrieve either a single piece of data or an entire document.

Oracle, Microsoft, and IBM don't want to concede their data-storage dominance to interlopers such as Ipedo and Tamino. The big three's databases also support XQuery, which is approaching final approval by the World Wide Web Consortium. It defines a means of accessing XML data from different sources and building new documents from it.

Digital Steps, a developer of apps for the energy industry, can manage XML data using XQuery with Gamma, its system for tracking energy suppliers' assets and inventories. Digital Steps used to have to modify or rebuild parts of Gamma for different customers, leading to maintenance complexities. Thanks to Oracle 10g's support of XML, "we're much closer to having a single standard platform across our client base," says Peter Black, managing director of Digital Steps.

Meanwhile, the American National Standards Institute, the standards-keeper of the SQL query language used by relational databases, is working on a version of the SQL/XML standard that will support XQuery in the next version of SQL, due out in 2007. Some vendors' databases already support the SQL/XML standard.