XML Gets Organized

Computerworld - When the Classwell Learning Group began building a database of online lesson plans and other information for teachers, it needed to store and access content ranging from word processing files to copy scanned from textbooks. Because it needed to store, access and query all those data types, the publisher chose an XML database product.

"XML was pretty much a no-brainer for us," says Brendan Collins, director of IT at Classwell, a division of publisher Houghton Mifflin Co. in Boston.

IT organizations are using XML for everything from integrating applications to content management and access control. Native XML databases can help with storing and managing the resulting flood of XML documents, but they're not the only option. Major databases now offer XML translator features that transform XML documents into fields within their relational structures. That transformation process can eliminate many of the benefits of using XML, however, so SQL database vendors say they're planning to add native XML capabilities to their products.

In the meantime, third-party vendors offer tools that they claim offer more complete integration among XML, relational and even flat-file databases.

Deciding which XML data store is right for you depends on whether you have a stable schema, or design, for your XML data; the degree to which you need to store and audit transactions in their original form; and whether the application is critical enough to justify the expense of a separate, native XML database, say users and software vendors.

XML is a hierarchical data description language that uses tags, such as "customer," to define the data components within a document. In contrast, relational databases such as Oracle, Microsoft SQL Server or IBM's DB2 organize data in well-defined rows and columns within tables.

The fact that XML documents carry not only the data but also the definitions of that data makes it easier for those documents to "describe themselves" to multiple applications during a transaction. Compared with SQL, XML is also much more capable of dealing with unstructured data and data that can be more dynamic in both its meaning and its structure, says Paul Hessinger, executive vice president of HealthRamp Inc. in New York. HealthRamp develops software that allows doctors to prescribe medications using handheld computers. "The permanent data we need to take care of we store in SQL Server. But as we move the data from a handheld device to a Web server, that's largely done via XML," he says.

Choosing an Approach

XML also makes it easier to change the type or format of data stored in a database, says Jake Freivald, director of marketing at iWay Software, a division of New York-based Information Builders Inc. that develops XML integration tools. In an XML database, he says, adding a business-address field to a database only requires creating an extra set of data description tags within the document. In a relational database, he says, that change would require a new set of tables for the business addresses and defining how those new tables relate to every existing table in the database.