View based Data Integration

Global As View (GAV), Local As View (LAV) or Global and Local As View (GLAV) approach.

view-based integration systems (VDISs): provide a single point of access to all underlying data sources. Users of a VDIS (or applications) would query the unified view and get back integrated results from all sources, whereas the task of combining data from the sources and resolving inconsistencies would handled by the system transparently to the applications.

VDISs made their first appearance in the form of multidatabases and federated systems [11]

1 Specifying the Relationship of the Sources with the Unified View

To allow the mediator to decide which data to retrieve from each source and how to combine them into the unified view, the administrator of the VDIShas to specify the correspondence between the local schema of each source and the global schema through mappings.

Global As View (GAV): the global database (schema) is expressed as a function of the local databases (schemas)
Local As View (LAV): local schema being described as a function over the global; LAV allows to add a source to the system independently of other sources.
Global and Local As View (GLAV): generalization of the two.

1.2 Local As View (LAV)

Query Answering in LAV: Since LAV mappings consist of an arbitrary query over the global schema, they may leave some information of the global database unspecified.

CROSS REFERENCE

Information Integration, Peer-to-Peer Data Integration, Query Rewriting Using Views, Schema Mapping