  Grid based systems require a database access mechanism that can provide
seamless homogeneous access to the requested data through a virtual data access
system, i.e. a system which can take care of tracking the data that is stored
in geographically distributed heterogeneous databases. This system should
provide an integrated view of the data that is stored in the different
repositories by using a virtual data access mechanism, i.e. a mechanism which
can hide the heterogeneity of the backend databases from the client
applications. This paper focuses on accessing data stored in disparate
relational databases through a web service interface, and exploits the features
of a Data Warehouse and Data Marts. We present a middleware that enables
applications to access data stored in geographically distributed relational
databases without being aware of their physical locations and underlying
schema. A web service interface is provided to enable applications to access
this middleware in a language and platform independent way. A prototype
implementation was created based on Clarens [4], Unity [7] and POOL [8]. This
ability to access the data stored in the distributed relational databases
transparently is likely to be a very powerful one for Grid users, especially
the scientific community wishing to collate and analyze data distributed over
the Grid.
