Design and implementation of a modern ASP grounder
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Zangari, Jessica
Leone, Nicola
Calimeri, Francesco
Perri, Simona
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Dottorato di Ricerca in Informatica. Ciclo XXX; Answer Set Programming (ASP) is a declarative programming paradigm proposed
in the area of non-monotonic reasoning and logic programming in the
late '80 and early '90. Thanks to its expressivity and capability of dealing with
incomplete knowledge, ASP that became widely used in AI and recognized as
a powerful tool for Knowledge Representation and Reasoning (KRR). On the
other hand, its high expressivity comes at the price of a high computational
cost, thus requiring reliable and high-performance implementations. Throughout
the years, a signi cant e ort has been spent in order to de ne techniques
for an e cient computation of its semantics. In turn, the availability of e cient
ASP systems made ASP a powerful tool for developing advanced applications in
many research areas as well as in industrial contexts. Furthermore, a signi cant
amount of work has been carried out in order to extend the basic language and
ease knowledge representation tasks with ASP, and recently a standard input
language, namely ASP-Core-2, has been de ned, also with the aim of fostering
interoperability among ASP systems.
Although di erent approaches for the evaluation of ASP logic programs have
been proposed, the canonical approach, which is adopted in mainstream ASP
systems, mimics the de nition of answer set semantics by relying on a grounding
module (grounder), that generates a propositional theory semantically equivalent
to the input program, coupled with a subsequent module (solver ) that
applies propositional techniques for generating its answer sets.
The former phase, called grounding or instantiation, plays a key role for
the successful deployment in real-world contexts, as in general the produced
ground program is potentially of exponential size with respect to the input
program, and therefore the subsequent solving step, in the worst case, takes
exponential time in the size of the input. To mitigate these issues, modern
grounders employ smart procedures to obtain ground programs signi cantly
smaller than the theoretical instantiation, in general.
This thesis focuses on the ex-novo design and implementation of a new modern
and e cient ASP instantiator. To this end, we study a series of techniques
geared towards the optimization of the grounding process, questioning the techniques
employed by modern grounders with the aim of improving them and
introducing further optimization strategies, which lend themselves to the integration
into a generic grounder module of a traditional ASP system following
a ground & solve approach. In particular, we herein present the novel system
I-DLV that incorporates all these techniques leveraging on their synergy to perform
an e cient instantiation. The system features full support to ASP-Core-2
standard language, advanced exibility and customizability mechanisms, and is endowed with extensible design that eases the incorporation of language upi dates and optimization techniques. Moreover, its usage is twofold: besides being
a stand-alone grounder, it is also a full- edged deductive database engine. In
addition, along with the solver wasp it has been integrated in the new version
of the widespread ASP system DLV recently released.; Università della CalabriaSoggetto
Artificial intelligence; Electronic instruments
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