Query mapping and transformation techniques for problem solving with multiple knowledge servers

Abstract: This paper describes a technique for infor-mation mediation when multiple heterogeneous knowl-edge and data servers are to be accessed during query processing. One problem is building an intelligent in-terface between each knowledge server (KS) and its processor (KP); and the second is to provide interoper-ability among multiple KP/KS so that a query may be answered using information from multiple sources. We present example scenarios which highlight these prob-lems and then outline query mapping and transforma-tion techniques that are applicable. The techniques for solving the interoperability problems involve rep-resentations in some canonical form. This includes a canonical representation (CR) corresponding to each KP/KS pair and a merged CR (MCR) to represent the mapping among the CRs. The MCR and CRs include relevant information obtained from a source query, and heterogeneous mapping (het-map) information, for all possible mappings among the multiple servers. The knowledge in the canonical form must be represented so that it can be easily accessed during query transfor-mation. We use an example of translating queries from an object schema to a relational schema to illustrate typical knowledge that must be represented in some canonical form. We use a high level logical language, F-logic, to represent the heterogeneous mapping (het-map) and query transformation information as a set of declarative rules, in the canonical form.