The stable release of the ibm_db2 PECL extension for IBM DB2, Cloudscape, and Apache Derby brought a high performing, highly functional database connectivity alternative to Unified ODBC for PHP 4 and 5 users. However, in and of itself a database extension does not enable you to use the many PHP applications that you might want to use. You either have to add a specific driver for each application that implements its own portability layer (such as phpMyFAQ), or if the application relies on one of the standard database abstraction layers (PEAR DB, MDB2, or ADOdb), then a driver needs to be added to the corresponding database abstraction layer.
To date, the standard database abstraction layers have offered support for DB2 only through the Unified ODBC extension (and despite substantial overlap in names, MDB2 does not offer support for DB2 at all). Due to some limitations of the Unified ODBC extension, access to DB2 would seem slow and buggy -- and access to Apache Derby or Cloudscape would be frought with minefields, as Unified ODBC does not provide a way of differentiating between the databases to which you are connected and their corresponding features. The ibm_db2 extension offers the db2_server_info() function which can tell you whether you are connected to DB2 on Linux, DB2 on a zSeries machine, or an Apache Derby database, and let your application or database abstraction layer perform the appropriate workarounds.
Now, however, as part of Larry Menard's efforts to enable Gallery 2, an ADOdb driver built on top of the ibm_db2 extension will, in all probability, be made available as part of a future ADOdb release. Undoubtedly there will be further testing to do, and tweaks and performance optimizations in the future code--for example, differentiating between the capabilities of Apache Derby and DB2--but this is a huge first step! Thanks to Larry and the Gallery 2 team for making this contribution.