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The conceptual and external schema descriptions may use different data models (e.g. relational, network, or semantic data models). ... In addition to the three schemas represented by boxes in Figure 1 , the ANSI,/SPARC architecture also contains a number of mappings, represented by edges in the diagram. ... used in  in order similarly to reduce the cost of processing queries in multidatabase systems using aggregate functions for overlapping data values. ...doi:10.1016/0020-0255(91)90044-u fatcat:cm5ht3htazhjlcdxwhhllwbtny