Ontology Based Query Processing for Global Information Systems 87 differential development within or even 9781402047152 differential development within or even between individuals could be determined by the differential replication of the various genetic elements or by their differential activity It is unquestionably true that they will play an increasingly dominant In Chapter 4 we detail the steps needed to access the data corre sponding to a query formulated over an ontology This work is a revision of the doctoral dissertation of Eduardo Mena pre sented to the Department of Computer Science and System Engineering at the University of Zaragoza (Spain) in November 1998 [Mena 98]