Karen, we're just getting started defining subtypes; Dissertation was just the first one we started trying to model, realizing that it had properties not likely to belong to any other "type" of Work. We can see that there may be lots of them, but agreeing on them will take some work.

And it's really the need for those additional properties that should drive the creation of new sub-types. If it's just a way of categorizing things, then genre or some other method of chunking can (and should) be used.

Tom