Query Translation

Up to now, the queries are reformulated into a form that refers directly to the data sources rather than the mediated schema. However, they are still in the data model of the mediated system. They should be translated into the data models of the data sources. This is performed by source-specific wrappers which will be defined in the following section. (** This is the responsibility of the source wrappers. We will be connecting Query Processing section to Data Extraction section briefly discussing the query translation stage inside query execution.)

(** We should also be discussing the flow of translation in the reverse direction, i.e., after the sources successfully perform the local queries, how the resuls are collected and combined into a single answer to present to the user)