Multiple overlapping classifications: issues and solutions

This paper discusses issues and solutions for supporting multiple overlapping classifications in database systems. These classifications are commonly found in science, although they are often ignored in computing applications for scientific data, and inappropriate solutions adopted as their replacement. Known database models and classification techniques offer some degree of support for multiple overlapping classifications, but do not fully support the basic features we have identified as necessary: trees/graphs, traceability, semantics of classifications, independence of classification and data, and identity of classifications. The approach to the problem adopted by the Prometheus project, based on an extended object-oriented database model and the independence of classification schemes from classified data, is presented and discussed.