  Knowledge can be represented compactly in multiple 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 integrity constraints, we identify classes of aggregators that
respect them in the aggregated database, provided these are satisfied in all
individual databases. We also characterise languages for first-order queries on
which the answer to a query 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 social choice theory to knowledge representation in databases.
