Graph should be binded to a single DataModel, but many Graph properties should be then be binded to a specific property of this DataModel:
-each series should be binded to a specific property (which would be a list). These properties would be the data.
-general Graph items like axis title should also be able to be binded to other properties, to allow more complex use. These properties would be the metadata.

As it is now, all the data are put in a single list (not developer friendly at all), and using metadata is impossible.