Chapter 9. The Database Zone

No matter what some industry pundits might say, the relational database is in no danger of being replaced by XML database servers anytime soon. Looking at the history of databases, we see that the idea of a hierarchical database is not a new one. The Information Management Systems of the 1950s and 1960s eventually evolved into the tree-oriented hierarchical databases that have been made all but obsolete by relational databases.

The truth is that relational databases can do a fair job of modeling hierarchical data, but hierarchical formats (such as XML documents) do a very poor job of simulating relational operations. But this doesn't mean that XML won't begin to play an integral part in moving information between databases and the systems that use them.

When talking about XML and databases, the questions arise: Where do you draw the line between the client application and the database? Should Microsoft's ActiveX Database Object (ADO) XML support be in the same category as Software AG's Tamino XML database? From the point of view of an application developer, it doesn't really matter where the data comes from. Whether it's stored in an RDBMS and converted to XML on the fly or whether it's served as a complete document from an application server, the only thing that an application developer needs to know is how to use it.

Before getting into the pros and cons of various approaches to integrating XML into back-office solutions, it is useful to have a high-level view of a basic scenario.