Boosting branch-and-bound MaxSAT solvers with clause learning

The Maximum Satisfiability Problem, or MaxSAT, offers a suitable problem solving formalism for combinatorial optimization problems. Nevertheless, MaxSAT solvers implementing the Branch-and-Bound (BnB) scheme have not succeeded in solving challenging real-world optimization problems. It is widely believed that BnB MaxSAT solvers are only superior on random and some specific crafted instances. At the same time, SAT-based MaxSAT solvers perform particularly well on real-world instances. To overcome this shortcoming of BnB MaxSAT solvers, this paper proposes a new BnB MaxSAT solver called MaxCDCL. The main feature of MaxCDCL is the combination of clause learning of soft conflicts and an efficient bounding procedure. Moreover, the paper reports on an experimental investigation showing that MaxCDCL is competitive when compared with the best performing solvers of the 2020 MaxSAT Evaluation. MaxCDCL performs very well on real-world instances, and solves a number of instances that other solvers cannot solve. Furthermore, MaxCDCL, when combined with the best performing MaxSAT solvers, solves the highest number of instances of a collection from all the MaxSAT evaluations held so far.

Undecidability of QLTL with two variables and one monadic predicate letter

We study the algorithmic properties of the quantified linear-time temporal logic QLTL in languages with restrictions on the number of individual variables as well as the number and arity of predicate letters. We prove that the satisfiability problem for QLTL in languages with two individual variables and one monadic predicate letter in Σ 11 -hard. Thus, QLTL is Π 11 -hard, and so not recursively enumerable, in such languages. The resultholds both for the increasing domain and the constant domain semantics and is obtained by reduction from a Σ 11 -hard N×N recurrent tiling problem. It follows from the proof for QLTL that similar results hold for the quantified branching-time temporal logic QCTL, and hence for the quantified alternating-time temporal logic QATL. The result presented in this paper strengthens a result by I. Hodkinson, F. Wolter, and M. Zakharyaschev, who have shown that the satisfiability problem for QLTL is Σ 11 -hard in languages with two individual variablesand an unlimited supply of monadic predicate letters.

EXPSPACE-Completeness of the Logics K4 × S5 and S4 × S5 and the Logic of Subset Spaces

It is known that the satisfiability problems of the product logics K4 × S5 and S4 × S5 are NEXPTIME-hard and that the satisfiability problem of the logic SSL of subset spaces is PSPACE-hard. Furthermore, it is known that the satisfiability problems of these logics are in N2EXPTIME. We improve the lower and the upper bounds for the complexity of these problems by showing that all three problems are in ESPACE and are EXPSPACE-complete under logspace reduction.

A Workflow Criticality-Based Approach to Bypass the Workflow Satisfiability Problem

Workflow management systems are very important for any organization to manage and model complex business processes. However, significant work is needed to keep a workflow resilient and secure. Therefore, organizations apply a strict security policy and enforce access control constraints. As a result, the number of available and authorized users for the workflow execution decreases drastically. Thus, in many cases, such a situation leads to a workflow deadlock situation, where there no available authorized user-task assignments for critical tasks to accomplish the workflow execution. In the literature, this problem has gained interest of security researchers in the recent years, and is known as the workflow satisfiability problem (WSP). In this paper, we propose a new approach to bypass the WSP and to ensure workflow resiliency and security. For this purpose, we define workflow criticality, which can be used as a metric during run-time to prevent WSP. We believe that the workflow criticality value will help workflow managers to make decisions and start a mitigation solution in case of a critical workflow. Moreover, we propose a delegation process algorithm (DP) as a mitigation solution that uses workflow instance criticality, delegation, and priority concepts to find authorized and suitable users to perform the critical task with low-security risks.

Modal context restriction for multiagent BDI logics

We present and discuss a novel language restriction for modal logics for multiagent systems, called modal context restriction, that reduces the complexity of the satisfiability problem from EXPTIME complete to NPTIME complete. We focus on BDI multimodal logics that contain fix-point modalities like common beliefs and mutual intentions together with realism and introspection axioms. We show how this combination of modalities and axioms affects complexity of the satisfiability problem and how it can be reduced by restricting the modal context of formulas.