The LDL system prototype

Abstract

The LDL system provides a declarative logic-based language and integrates relational database and logic programming technologies so as to support advanced data and knowledge-based applications. This paper contains a comprehensive overview of the system and contains a description of the LDL language and the compilation techniques employed to translate LDL queries into target queries on the stored data. The paper further contains a description of the architecture and runtime environment of the system and the optimization techniques employed in order to improve the performance and assure the safety of the compiled queries. The paper concludes with an account of the experience gained so far with the system, and discusses application areas where the LDL approach appears to be particularly effective.

Non-determinism in deductive databases

“…Observe here that we have used a suitable compact notation for recognizing all true dif f Choice literals so that the problem of infinite domains is overcome. In the actual implementation, this is also easy to do by not storing dif f Choice and ¬dif f choice explicitly, and simply deriving their values from those of chosen as needed [Chi90].…”

“…As a final remark, a realistic implementation of the above algorithm does not actually compute the dif f Choice relation, but simply records the chosen tuples as they are generated in order to discard or not the future candidates. Therefore, choice can be implemented, as it is done in LDL [Chi90] by simply memoing old values of chosen [Die87].…”

Towards intelligent databases

“…From discussions we had with designers of various database system prototypes (e.g. [54,3,23,26,33,34,40,66,68,20,69]) we gained the impression that meta-programming techniques are rather widely applied, although often quite unconsciously, in implementing database systems. The systematic investigation of this techniques for database system design is, we think, a promising direction of research.…”

“…[28,29,30,31,65,21,8,48,64,17,18,44,45] for an overview), and experimental deductive database management systems have been and are still implemented (e.g. [54,9,23,26,32,34,51,56,66,33,68,40,52]). Industrial products are currently developed from research prototypes (e.g.…”

Key Constraints and Monotonic Aggregates in Deductive Databases

“…For concreteness, we use the aggregate constructs of LDL++ [4], but very similar syntactic constructs are used by other systems (e.g., CORAL [23]), and the semantics here proposed is general and applicable to every logic-based language and database query language.…”