OmniGraffle files are stored in Apple Plist format, which can be read with the plist gem. This gem decorates the resulting structure with methods that make working with Graffle files more pleasant.
At the moment, you should only use the methods if you're treating the structure as read-only. Support for mutating Graffle files may come.
The main motivation for this exercise is to use Graffle files as Rails integration tests. Such a test looks like this: