  Knowledge can be represented compactly in a multitude ways, from a set of
propositional formulas, to a Kripke model, to a database. In this paper we
study the aggregation of information coming from multiple sources, each source
submitting a database modelled as a first-order relational structure. In the
presence of an integrity constraint, we identify classes of aggregators that
respect it in the aggregated database, provided all individual databases
satisfy it. We also characterise languages for first-order queries on which the
answer to queries on the aggregated database coincides with the aggregation of
the answers to the query obtained on each individual database. This
contribution is meant to be a first step on the application of techniques from
rational choice theory to knowledge representation in databases.
