When service S is the definitiveService for property P,
any statement X P Y is true iff and only if a query to S returns
that it is. The protocol for the service S depends on the scheme.
For mysql protocol, the URI of the service is like
sql://user:password@host.domain/database/.
For example, there may be a definitive service for the zipcode of
airports by airport code, and so on. This is useful to let a reasoner
know that it can help resolve a query by delegating it to the service
in question.
(Cwm will do this if its mode includes "r").