I keep finding myself reverse engineering databases in order to understand the underlying data model. There are a bunch of tools out there that will do this including DeZign and ModelRight, both of which are PC only. I generally work on a Mac but have my old PC as a backup. Anyway, it turns out that Visio has a reverse engineer feature. You need to open a new document with the Database ERD stencil and a menu option appears. It works using the Windows ODBC connections, so you’ll need to set that up. I had to download the MySQL ODBC drivers for Windows, and then it was off running. Annoyingly, the table relationships do not get defined unless the original data model has them defined, so that could be some work depending on the scope and complexity of your database, but its a good start nonetheless.