On the IBM developerWorks website there's a new tutorial (part 2 of the series, here's part 1) about creating the DB2 Health Monitor sample app:

DB2 9 pureXML technology allows businesses to improve data integrity and avoid legacy data lock-in. It enables application developers to utilize the best storage medium for the task and eliminate the middle-tier application logic previously required to take advantage of Web services.

PHP's role in the creation is to generate the XML that the system needs to communicate between the application and the database.