Abstract
We consider the problem of query execution when there is limited access to the relations, i.e. when binding patterns require values to be specified in order to get data from the relation. This problem is common in virtual data integration systems where there are heterogeneous sources with various restricted access patterns and query capabilities. Another problem is the lack of the statistical information about the sources and occurrence of unpredictable events. We introduce two mobile join operators, MDJoin and SMDJoin which are designed for restricted sources and implemented using 'mobile agents' in order to benefit from their autonomous and reactive characteristics. Mobile operators of restricted sources are capable to deal with restricted sources and react to the variations between the compile-time estimations and run-time computations of data during query execution. The difference between the two new query operators lies in their level of adaptation ability to the execution environment. Performance results show that mobile agent-based approach at operator level can lead to a significant reduction in response time with restricted sources.
Highlights
The goal of virtual data integration systems is to support seamless access to heterogeneous data sources
Due to the reasons of privacy or performance issues, we cannot retrieve information from these sources without providing input values. Dealing with such restricted sources, brings out various issues to be studied in terms of providing simple concept of modeling for the source descriptions and query capabilities, query execution plan generation solving the complexity caused by the source restrictions and query execution operators that are able to work efficiently despite of the source restrictions
The related work whose primary focus is restricted sources consists of three groups of efforts; (i) modeling the heterogeneity of the sources in terms of access restrictions and query capabilities [18,25], (ii) generating valid, efficient and complete query execution plans in the level of the optimizer [4,13,15,19,21,25] and (iii) developing query execution operators handling restricted access [5,17]
Summary
The goal of virtual data integration systems is to support seamless access to heterogeneous data sources. The related work whose primary focus is restricted sources consists of three groups of efforts; (i) modeling the heterogeneity of the sources in terms of access restrictions and query capabilities [18,25], (ii) generating valid, efficient and complete query execution plans in the level of the optimizer [4,13,15,19,21,25] and (iii) developing query execution operators handling restricted access [5,17]. To our knowledge there is no work to demonstrate the impact of software mobility in decentralized adaptive query processing at operator level concerning the source restrictions in a virtual data integration environment.
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