  A query Q is monotonically determined over a set of views if Q can be
expressed as a monotonic function of the view image. In the case of relational
algebra views and queries, monotonic determinacy coincides with rewritability
as a union of conjunctive queries, and it is decidable in important special
cases, such as for CQ views and queries. We investigate the situation for views
and queries in the recursive query language Datalog. We give both positive and
negative results about the ability to decide monotonic determinacy, and also
about the co-incidence of monotonic determinacy with Datalog rewritability.
