Windchill UML Model Documentation - English
User Role: Developer
Published: 24-Jun-2014
Direct Link: https://support.ptc.com/view?im_dbkey=31185
It is a large zip file. You have to download the zip, unzip it, then open the main HTML file. I can't remember which one is the main HTML file, but just try a few until you find the portal page.
Once you have the portal page, you can click around. Please note that we have had trouble with this on some versions of IE, so if you have problems, then try a different browser.