Omnigraffle file format

Im trying to develop some scripts, and I’ve hit a stumbling block, the format seems broken.
If i try to use the apple plist formatting tools to convert an ipad created omnigraffle file, i get this error. which stops me even beginning to work on my scripts.

plutil -convert xml1 -o - data.plist 
data.plist: Property List error: Unexpected character  at line 1 / JSON error: JSON text did not start with array or object and option to allow fragments not set.

I LOVE Omnigraffle on the iPad, and I really want to keep using it, but without the ability to develop these scripts, its becoming a productivity impediment because I have to spend too much time converting Omnigraffle files into. Im not looking for someone else to build this for me, i just need to know how to break open the omnigraffle file so i can feast on the delicious productivity juices inside and make what i need to make.

OmniGraffle always uses XML as its underlying data format, but it sometimes compresses that XML using gzip. Does gzcat data.plist get your data into the format you’re expecting?