Progressive restriction on enumerated types in Owl

[David R. Throop]

How does one progressively restrict enumerated types in Owl?

I've got an ontology of function-terms. I want to map
English-language terms (as strings) to the function terms. I want to
restrict the mapping as I go down the hierarchy. In the (very
stripped down) example, FUNCTION can map to any of the four terms, but
its sub-sub-subclass INCREASE_QUANTITY only maps to 'produce.'

FUNCTION Hierarchy MAPPED TERMS

FUNCTIONS happen | convert | produce | consume
PROCESSES convert | produce | consume
CHANGE_QUANTITY produce | consume
INCREASE_QUANTITY produce
DECREASE_QUANTITY consume
The reference at http://www.w3.org/TR/owl-ref/#EnumeratedDatatype
shows me how to enumerate the possible values for the Mapped term.
But I don't see how I can restrict it as I go down the tree.

Any ideas, suggestions?

And is comp.text.xml a good place to ask this?

Thanks
David Throop