The Zend Developer Zone has a new post today that points out a two part series from the IBM developerWorks pages that covers the creation and use of a U2-PDO driver.
The PHP Data Objects (PDO) extension provides a lightweight, convenient means for accessing databases in PHP. In this article, you'll learn how to write a PDO driver for U2 using the U2 native interface, InterCall. With this PDO driver, U2 users can develop PHP applications that access U2 data quickly and easily.
Part one gives a brief introduction to PHP Data Objects followed by a look at the U2 InterCall Interface to prepare the reader. Then it's into the code - first the code to access the InterCall interface (the main part of the tutorial), then compiling PHP with the extension, and finally testing it out. They also include a few more testing examples you can use to understand a bit more how it all works.
Part two picks right up where part one left off and starts the development of a sample application consisting of a simple login screen and a file listing that, using Ajax, grabs the details about a file and displays them to the browser.
Cal also suggests you check out Sara Golemon's tutorials (part one, part two, and part three) to get you up to speed on extension writing if you're new to the game.