  Matching dependencies (MDs) have been recently introduced as declarative
rules for entity resolution (ER), i.e. for identifying and resolving duplicates
in relational instance $D$. A set of MDs can be used as the basis for a
possibly non-deterministic mechanism that computes a duplicate-free instance
from $D$. The possible results of this process are the clean, "minimally
resolved instances" (MRIs). There might be several MRIs for $D$, and the
"resolved answers" to a query are those that are shared by all the MRIs. We
investigate the problem of computing resolved answers. We look at various sets
of MDs, developing syntactic criteria for determining (in)tractability of the
resolved answer problem, including a dichotomy result. For some tractable
classes of MDs and conjunctive queries, we present a query rewriting
methodology that can be used to retrieve the resolved answers. We also
investigate connections with "consistent query answering", deriving further
tractability results for MD-based ER.
