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Authors: Dodaro, Carmine

Article Type: Research Article

Abstract: Answer Set Programming (ASP) is a declarative language oriented towards solving complex combinatorial problems. In fact, ASP has been successfully used to address problems in various academic and industrial domains. The success of ASP can be attributed to its concise syntax, intuitive semantics, and the availability of several efficient solvers based on the Conflict-Driven Clause Learning (CDCL) algorithm. This paper details the design and implementation of contemporary CDCL solvers, emphasizing both algorithmic descriptions and their effective and efficientimplementation.

Keywords: Answer set programming, efficient solvers, conflict-driven clause learning

DOI: 10.3233/IA-240019

Citation: Intelligenza Artificiale, vol. 18, no. 2, pp. 239-259, 2024

Authors: Alviano, Mario | Dodaro, Carmine

Article Type: Research Article

Abstract: Modern, efficient Answer Set Programming solvers implement answer set search via non-chronological backtracking algorithms. The extension of these algorithms to answer set enumeration is nontrivial. In fact, adding blocking constraints to discard already computed answer sets is inadequate because the introduced constraints may not fit in memory or deteriorate the efficiency of the solver. On the other hand, the algorithm implemented by CLASP , which can run in polynomial space, requires to modify the answer set search procedure. The algorithm is revised in this paper so as to make it almost independent from the underlying answer set search procedure, provided …that the procedure accepts as input a logic program and a list of assumption literals, and returns an answer set (and associated branching literals). In fact, thanks to an alternative view in terms of transition systems, the revised algorithm is suitable to easily accommodate the enumerate of models of other Boolean languages, among them classical models of propositional theories. On a pragmatic level, the paper presents two implementations of the enumeration algorithm, in WASP for answer set enumeration, and in GLUCOSE for classical models enumeration. The implemented systems are compared empirically to the state of the art solver CLASP . Show more

Keywords: Answer Set Programming, Enumeration, Assumption Literals

DOI: 10.3233/FI-2019-1809

Citation: Fundamenta Informaticae, vol. 167, no. 1-2, pp. 31-58, 2019

Authors: Alviano, Mario | Dodaro, Carmine

Article Type: Research Article

Abstract: Many efficient algorithms for the computation of optimum stable models in the context of Answer Set Programming (ASP) are based on unsatisfiable core analysis. Among them, algorithm OLL was the first introduced in the context of ASP, whereas algorithms ONE and PMRES were first introduced for solving the Maximum Satisfiability problem (MaxSAT) and later on adapted to ASP. In this paper, we present the porting to ASP of another state-of-the-art algorithm introduced for MaxSAT, namely K , which generalizes ONE and PMRES . Moreover, we present a new algorithm called OLL-IN-ONE that compactly encodes all aggregates of OLL by taking …advantage of shared aggregate sets propagators. The performance of the algorithms have been empirically compared on instances taken from the latest ASP Competition. Show more

Keywords: Answer Set Programming, weak constraints, unsatisfiable core analysis

DOI: 10.3233/FI-2020-1974

Citation: Fundamenta Informaticae, vol. 176, no. 3-4, pp. 271-297, 2020

Authors: Alviano, Mario | Dodaro, Carmine | Maratea, Marco

Article Type: Research Article

Abstract: The goal of the Nurse Scheduling Problem is to find an assignment of nurses to shifts according to specific requirements. Frequently, a computed schedule may become not usable because of sudden absences of some nurses. In this cases, Nurse Rescheduling amounts to the computation of a new schedule, which has to satisfy the original requirements and the new absences. Additionally, a good solution to the Nurse Rescheduling Problem must be as similar as possible to the original schedule, which practically means that the number of changes has to be minimized. This paper focuses on the requirements specified by an Italian …hospital, and recently addressed by an approach based on Answer Set Programming (ASP). Even if promising results have been obtained with ASP, the original encoding presents some intrinsic weaknesses, which are identified and eventually circumvented in this paper. The new encoding is designed by taking into account both intrinsic properties of Nurse Scheduling and internal details of ASP solvers, such as cardinality and weight constraint propagators. The performance gain of clingo and wasp is empirically verified on instances from ASP literature. As an additional contribution, the performance of clingo and wasp is compared to other declarative frameworks, namely SAT and ILP; the best performance is obtained by clingo running the new ASP encoding. The advanced ASP encodings are then extended to solve Nurse Rescheduling, and an empirical evaluation is conducted with clingo and wasp . Show more

DOI: 10.3233/IA-170030

Citation: Intelligenza Artificiale, vol. 12, no. 2, pp. 109-124, 2018

Authors: Dodaro, Carmine | Galatà, Giuseppe | Maratea, Marco | Porro, Ivan

Article Type: Research Article

Abstract: The Operating Room Scheduling (ORS) problem is the task of assigning patients to operating rooms, taking into account different specialties, the surgery and operating room session durations, and different priorities. Given that Answer Set Programming (ASP) has been recently employed for solving real-life scheduling and planning problems, in this paper we first present an off-line solution based on ASP for solving the ORS problem. Then, we present techniques for re-scheduling on-line in case the off-line schedule can not be fully applied. Results of an experimental analysis conducted on benchmarks with realistic sizes and parameters show that ASP is a suitable …solving methodology also for the ORS problem. This analysis has been performed with a web framework for managing ORS problems via ASP that allows a user to insert the main parameters of the problem, solve a specific instance, and show results graphically in real-time. Show more

DOI: 10.3233/IA-190020

Citation: Intelligenza Artificiale, vol. 13, no. 1, pp. 63-77, 2019