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We consider query answering on Description Logic DL ontologies with DBoxes, where a DBox is a set of assertions on individuals involving atomic concepts and roles called DBox predicates. The extension of a DBox predicate is exactly defined in every interpretation by the contents of the DBox, i.e., a DBox faithfully represents a database whose table names are the DBox predicates and the tuples are the DBox assertions. Our goals are i to find out whether the answers to a given query are solely determined by the DBox predicates and, if so, ii to find a rewriting of the query in terms of them. The resulting query can then be efficiently evaluated using standard database technology. We have that i can be reduced to entailment checking and ii can be reduced to finding an interpolant. We present a procedure for computing interpolants in the DL ALC with general TBoxes. We extend the procedure with standard tableau optimisations, and we discuss abduction as a technique for amending ontologies to gain definability of queries of interest.