Developments in our ability to integrate and analyse data held in existing heterogeneous data resources can lead to an increase in our understanding of biological function at all levels. However, supporting ad hoe queries across multiple data resources and correlating data retrieved from these is still difficult. To address this, we are building a mediator based on the functional data model database, P/FDM, which integrates access to heterogeneous, distributed biological databases, while making use of existing search engines and indexes, without infringing on the autonomy of the underlying databases. Central to our design philosophy is the use of schemas. We have adopted a federated architecture with a five-level schema, arising from the use of the ANSI-SPARC three-level schema to describe both the existing autonomous data resources and the mediator itself. We describe the use of mapping functions and list comprehensions in query splitting, producing execution plans, code generation and result fusion. We give an example of cross-database querying involving data held locally in P/FDM systems and external data in SRS.
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