Non-Deterministic Choice in Datalog

Non-determinism in deductive databases

“…The problem of non-determinism in the framework of database logic languages was first addressed in [KN88], where an elegant solution based on the notion of minimal model and functional dependencies is proposed. According to [KN88,NT89], special goals, of the form choice((X), (Y )), are allowed in the rules to denote the functional dependency (FD) X → Y [Ull90].…”

“…According to [KN88,NT89], special goals, of the form choice((X), (Y )), are allowed in the rules to denote the functional dependency (FD) X → Y [Ull90]. Then the meaning of such programs is defined by its choice models, as discussed next.…”

“…The desire to express applications as those above, where non-deterministic queries and modeling of non-deterministic behavior are needed, provided the original motivation for the introduction of the choice construct [KN88]. Only more recently, these authors became fully aware of the important role that these non-deterministic constructs can play in computing deterministic queries or transformations.…”

“…We show that the current proposal, namely the choice proposal described in [KN88] and [NT89] suffers from undesirable properties that follow from its static nature. Thus, we introduce a new definition called dynamic choice that cures the problems of the construct proposed in [KN88]-which will hereafter be referred to as static choice.…”

“…We show that the current proposal, namely the choice proposal described in [KN88] and [NT89] suffers from undesirable properties that follow from its static nature. Thus, we introduce a new definition called dynamic choice that cures the problems of the construct proposed in [KN88]-which will hereafter be referred to as static choice. The declarative semantics of such a construct is based on the concept of stable models: the multiplicity of stable models for a given program provides a model theoretical characterization of non-determinism [SZ89].…”