INCOMPLETE INFORMATION AND THE FUNCTIONAL DATA MODEL

This paper presents an experimental functional database language Fudal which is a further development of our group's work on persistent func tional database languages. In this latest work we consider how unknown or partially known information can be treated in the functional conte xt. The language we have implemented, Fudal,includes certainty and pos sibility operators. We outline the problems that are caused by the use of null values and truth functional logic in conventional database la nguages, and show how these problems can be overcome by defining the s emantics of queries of a database containing partial information in te rms of its 'completions'. If D is a database containing partial inform ation then a completion of D is a database which is consistent with D and contains no partial information. We demonstrate that, even when a database has a large number of completions, sensible queries can be co nstructed using certainty and possibility operators. Finally we show h ow these operators can be implemented and discuss the use of Fudal in practical contexts.