Laurent Siklóssy, Jean-Louis Laurière
The principal restrictions previously placed on the relational data base model have been removed in the L2 model presented here. We extend the model to include null (i.e. unknown and non-relevant) values (even in keys), repetitions of tuples, functional dependencies, a very rich set of constraints and information originating from several sources. The programmed problem-solver ALICE is utilized to manipulate the constraints and to simplify relations: to answer a query, ALICE selects both the tuples which might answer the query upon appropriate substitutions for unknown values.