Finding Candidate Keys and 3NF via Strategic Port Graph Rewriting

We present new algorithms to compute candidate keys and third normal form design of a relational database schema, using strategic port graph rewriting. More precisely, we define port graph rewriting rules and strategies that implement a candidate key definition and Ullman’s algorithm to decompose a relation schema into lossless 3NF schemata. We show the correctness of the resulting database schema by proving soundness, completeness and termination of our strategic graph programs. These rules and strategies provide a declarative and visual description of the algorithms, and permit a fine-grained analysis of the computation steps involved in the normalisation process. The algorithms have been implemented in Porgy, a visual, interactive modelling tool.