Accessing Underlying Data Repositories

In this chapter we explain the task performed by the Ontology Server accessing the data repositories underlying an ontology. First, we present some definitions used to describe data repositories. Second, we introduce the formal description of the mapping information utilized. Third, we explain the different steps followed to access underlying data corresponding to a query formulated over an ontology, and we illustrate them with the help of an example. And finally, we comment on certain interesting issues related to correlation and presentation steps.