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Managing data sources with XSLT: an approach to transform any type of data source to XML. (XML & XSLT).

Article Excerpt
I and a colleague were working on a research project when we saw an opportunity to approach our data management from a different angle, XML appeared on the scene, and when IBM alpha Works released its first parser we were on our way, using XML to solve our data access problems.

During several Department of Defense research projects since the mid-1990s, my colleague and I have had the opportunity to explore various techniques for accessing different types of data sources using XML. These data sources include relational databases, CORBA objects, flat files, and, more recently, LDAP and the J2EE Connector architecture. Initially we used JDBC to access the relational data sources. The JDBC code was tedious to write, however, and difficult to update when new database schemas were released.

XML As a Data Access Language

We started out using XML as a way to specify the common parts of our JDBC code. This provided a static approach for defining our basic access requirements--such as the database URL and our queries--as data within elements of the XML document. We could then hand this document, with the embedded instructions, to a database manager and tell it to pass back a result set by running a specified query. This approach did give us the flexibility of placing our queries in an external file, but the source code required to implement the result set processing was more than we wanted to write and maintain. This document structure was also limited because conditional processing and multiple database accesses were difficult to express as straight XML in the document.

The client part of our program was already completely dynamic. Everything about the client, including the menu bar and dialog boxes, was defined by property files, and the code needed to run the interface wasn't known until runtime. We took the lessons learned from the client side and applied them to the server side of the program. Our desire for a completely dynamic processing engine on the server side pushed us to look deeper for ways to use XML technologies to manipulate data sources without writing any Java code.

Along the way we looked at using XSLT to provide a conditional execution and transformation environment. This turned out to be exactly what was needed. XSLT provided the technology necessary to make our static documents dynamic. The next step was to make our instruction set dynamic and build an extensible processing engine for the instructions.

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