Some time ago, when we moved from OWB 9 to 10, I noticed the size of OWB exports into mdl files dramatically decreased. That was a good thing in that it was easier to distribute the mdl files e.g. to production sites. It it also meant you could not read (or edit) the contents of the mdl files any more. I always assumed the new mdl format was some kind of binary optimized format, but today I read this blog from the OWB guys. And it turns out that the ‘new’ format is just a normal zip file containing 2 files. And that you can specify the export to be done in the ‘old’ text format. Text you can edit!
It could be a means to move/copy one or more mappings from one project to another project. Not easy as you must ‘hack’ the mdl file, but it can be done. Neat.