8 research outputs found
Constraints, Lazy Constraints, or Propagators in ASP Solving: An Empirical Analysis
Answer Set Programming (ASP) is a well-established declarative paradigm. One
of the successes of ASP is the availability of efficient systems.
State-of-the-art systems are based on the ground+solve approach. In some
applications this approach is infeasible because the grounding of one or few
constraints is expensive. In this paper, we systematically compare alternative
strategies to avoid the instantiation of problematic constraints, that are
based on custom extensions of the solver. Results on real and synthetic
benchmarks highlight some strengths and weaknesses of the different strategies.
(Under consideration for acceptance in TPLP, ICLP 2017 Special Issue.)Comment: Paper presented at the 33nd International Conference on Logic
Programming (ICLP 2017), Melbourne, Australia, August 28 to September 1,
2017. 16 page
Enhancing and Applying Answer Set Programming: Lazy Constraints, Partial Compilation and Question Answering
Dottorato di Ricerca in Matematica ed Informatica. Ciclo XXXIThis work is focused on Answer Set Programming (ASP), that is an expressive
formalism for Knowledge Representation and Reasoning. Over time,
ASP has been more and more devoted to solving real-world problems thanks
to the availability of e cient systems. This thesis brings two main contributions
in this context: (i) novel strategies for improving ASP programs
evaluation, and (ii) a real-world application of ASP to Question Answering
in Natural Language.
Concerning the rst contribution, we study some cases in which classical
evaluation fails because of the so-called grounding bottleneck. In particular,
we rst focus on cases in which the standard evaluation strategy is ine ective
due to the grounding of problematic constraints. We approach the problem
using custom propagators and lazy instantiators, proving empirically when
this solution is e ective, which is an aspect that was never made clear in
the existing literature. Despite the development of propagators can be effective,
it has two main disadvantages: it requires deep knowledge of the
ASP systems, and the resulting solution is not declarative. We propose a
technique for overcoming these issues which we call program compilation.
In our approach, the propagators for some of the logic rules (not only for
the constraints) of a program are generated automatically by a compiler.
We provide some su cient conditions for identifying the rules that can be
compiled in an approach that ts a propagator-based system architecture.
An empirical analysis shows the performance bene ts obtained by introducing
(partial) compilation into ASP programs evaluation. To the best of our
knowledge, this is the rst work on compilation-based techniques for ASP.
Concerning the second part of the thesis, we present the development of a
Natural Language Question Answering System whose core is based on ASP.
The proposed system gradually transforms input questions into SPARQL
queries that are executed on an ontological knowledge base. The system
integrates several state-of-the NLP models and tools with a special focus
on the Italian language and the Cultural Heritage domain. ASP is used to
classify questions from a syntactical point of view. The resulting system is the
core module of the PIUCULTURA project, funded by the Italian Ministry of
Economic Development, that has the aim to devise a system for promoting
and improving the fruition of Cultural Heritage.UniversitĂ della Calabri
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