I'm happier at the command line, but needed some graphical representation of information and easy ways to export example queries for the book I'm working on. I noticed that phpMyAdmin now has a Designer tab, which shows relationships between tables and allows you to define them.

She includes two screenshots of the process of setting up a foreign key on two tables. You can find lots more articles related to the designer view here.

MDB2_Schema_Writer is the responsible for dumping a database schema to a XML file. It walks into a database definition and outputs the correspondent XML tags.

He gives an example of checking a table (in $table) to see if it has constraints and check its validity. If everything's okay, the script pushes data into a buffer of specially formatted XML data.