Abstract
The benefits of using an ontology over relational data sources to mediate the access to these data are widely accepted and well understood. However, building such ontologies is a time consuming and error-prone process. Recently this problem has been tackled by proposing a technique for automatically wrapping the relational data sources by means of an ontology. In this paper we address the problem of supporting the ontology engineer in the task of enriching of such ontologies. In fact, changes to the ontology can be unsupported by the underlying data sources; which means that it is likely that queries against the enriched ontology return empty answers. To avoid this problem the ontology must be carefully handcrafted, and we propose a first step towards the automatic support of this task. We provide an algorithm, based on query reformulation, for verifying emptiness of a term in the enriched ontology with respect to the data sources. Moreover, we show how this algorithm can be applied to guide the user in designing meaningful wrappers.