Google provides great documentation for KML, but their diagram leaves much to the imagination. I looked around for a more complete diagram of KML 2.2 that I could use as a quick reference, but couldn’t find any so I made one myself. I did it using MyEclipse’s UML modeling tool, which has some irritating quirks, but for the most part is reliable. The diagram is Java-centric and doesn’t include every object, though most of the important stuff is there.
Click on the image to see the entire diagram. Here’s the actual My Eclipse UML file. If you make any corrections or enhancements, please send me an update.