PostgreSQL has a /very/ nice system of creating user-defined types,
I guess I was not clear. I am very aware of PostgreSQL's excellent
type system and have written several types myself. However, I am
looking for something broader: published papers in the database
literature on the rationale for and design of datatypes that go beyond
the "standard" set to represent more complex "real-world"
information. I understand this is not necessarily
PostgreSQL-specific, but I expect that there are people here more
knowledgable of the database literature than myself and that
PostgreSQL's extensible type system might attract people who have
given the issue some thought. Sorry if this is too off-topic.
Cheers,
Brook