Providing quality responses with natural language interfaces: the null value problem

An underlying relational database model and the database query language SQL are assumed, and methods are presented for responding with appropriate answers to null value responses. This is done by using a knowledge base based on RM/T, an extended relational model. The advantages of this approach are described. To demonstrate the utility of the knowledge base model, a simple knowledge base is constructed. The algorithms that provide additional information when a null answer is returned are detailed