A language for updating logic programs and its implementation

Nicola Leone, Luigi Palopoli, Massimo Romeo
1995 The Journal of Logic Programming  
This paper proposes an update language, called ULL, for knowledge systems based on logic programming. This language is built upon two basic update operators, respectively denoting insertion and deletion of a positive literal (atom). Thus, simple control structures are defined for combining the basic updates into programs capable of expressing complex updates. The semantics of the update language is centered around the idea of executing a basic update by directly modifying the truth valuation of
more » ... that (intensionally or extensionally defined) atom which is the object of the update. This modification propagates recursively to the truth valuations of those atoms dependent upon the updated one. The expressive power of this language is discussed, its implementation is studied, and an interpreter is given, which is proven correct w.r.t, the defined formal semantics. The computational complexity of the proposed implementation is also analyzed, showing that the update language interpreter runs efficiently. Finally, three extensions to ULL are discussed. The first allows the programmer to insert and delete rules, the second supports a form of hypothetical reasoning about updates, and the last introduces facilities in the language for the definition and the calling of update procedures. <1
doi:10.1016/0743-1066(94)00025-2 fatcat:rhuekdv57rgdtjc3x24vaz25ue