Integration System based on both GAV and LAV query processing approaches
نویسندگان
چکیده
Data Integration is the process of combining data residing at different sources with associated local schemas to form a single virtual database with an associated global schema [1, 2]. This is to provide the user with a uniform query interface for multiple independent heterogeneous data sources [3, 4]. There are four main approaches of data integration. They are Global As view (GAV), Local As View (LAV), Global Local As View (GLAV) and Both As View (BAV). BAV is known as the best data Integration approach as it does not have any of the drawbacks of GAV, LAV and GLAV approaches. The unique feature of the BAV is that the constructs of global schema can be extracted as views over the sources (feature of GAV) and the constructs of sources can also be extracted as the views over the global schema (feature of LAV). Therefore, it is possible to implement both the GAV and LAV based query processing approaches for a BAV based data integration system. AutoMed is the first data integration system based on the BAV approach. Currently it uses the feature of the GAV that BAV approach supports for query processing. However, the GAV based data integration systems cannot derive the global schema constructs that do not have equivalent source schema constructs, as views over the sources. Therefore, they cannot answer any queries on those global schema constructs. However, the LAV based systems can derive some of the source schema constructs as views over those constructs of the global schema. Therefore, they can answer any queries on those global schema constructs. On the other hand, the LAV based data integration systems cannot derive the source schema constructs that do not have equivalent global schema constructs, as views over the global schema. Therefore, they cannot answer any queries on those source schema constructs. However, the GAV based systems can derive some of the global schema construct as views over those constructs of the sources. Therefore, they can answer any queries on those source schema constructs. So, a Data Integration system based on both approaches would not have the drawbacks of both the GAV and LAV based data integration systems. Currently, there is no data integration system based on both of these approaches. Therefore, it is decided to use the feature of LAV that is supported by the BAV approach to implement a LAV based query processing approach. Then, we can …
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