Pseudo-Boolean optimization (PBO) is usually used to model combinatorial optimization problems, especially for some real-world applications. Despite its significant importance in both theory and applications, the performance of current PBO solvers is still limited. This paper develops a novel local search algorithm for PBO, which has four main ideas. First, we design a new primary scoring function and a two-level selection strategy to evaluate all candidate variables. Second, we introduce a new weighting scheme to accurately guide the search process toward more promising directions. Third, we propose a novel deep optimization strategy to disturb some search processes. Fourth, an efficient solution space exploration mechanism is applied to help the algorithm jump out of local optimum. We conduct experiments on a broad range of public benchmarks, including three large-scale practical application benchmarks, two benchmarks from PB competitions, an integer linear programming optimization benchmark, a crafted combinatorial benchmark, and a combinatorial optimization knapsack benchmark to compare our proposed algorithm against twelve state-of-the-art competitors, including seven recently-proposed pure stochastic local search PBO solvers, a non-traditional stochastic local search combined with complete oracle, two complete PB solvers, and two mixed integer programming (MIP) solvers. Our proposed algorithm has been shown to perform best on these three real-world benchmarks. On the other five benchmarks, our algorithm shows competitive performance compared to state-of-the-art competitors, and it significantly outperforms all other local search algorithms, indicating that our algorithm greatly advances the state of the art in local search for solving PBO.

Abstract UPPAAL is a formal modeling and verification tool based on timed automata, capable of effectively analyzing real‐time software and hardware systems. In this article, we investigate research on UPPAAL‐assisted formal modeling and verification. First, we propose four research questions considering tool characteristics, modeling methods, verification means and application domains. Then, the state‐of‐the‐art methods for model specification and verification in UPPAAL are discussed, involving model transformation, model repair, property specification, as well as verification and testing methods. Next, typical application cases of formal modeling and verification assisted by UPPAAL are analyzed, spanning across domains such as network protocol, multi‐agent system, cyber‐physical system, rail traffic and aerospace systems, cloud and edge computing systems, as well as biological and medical systems. Finally, we address the four proposed questions based on our survey and outline future research directions. By responding to these questions, we aim to provide summaries and insights into potential avenues for further exploration in this field.

Propositional model counting is the problem of computing the satisfying assignments count of a given CNF formula. Due to the weak solving ability of the existing exact model counters in large-scale problems, approximate model counting has been proposed as a practical alternative to exact model counting. Most of the best current approaches are based on XOR constraints for approximate model counting, also known as the hashing-based method. In this paper, a new approximate model counter using short XOR constraints is proposed, which integrates bounded solving and controllable randomisation. By constantly adding short XOR constants, the solution space has been reduced to a smaller one. However, a smaller scale of solution space may result in worse result accuracy. Therefore, by limiting the scale of solution space that applies XOR constraints, bounded solving effectively increases the accuracy of a model counter. Controllable randomisation makes use of backbone variables and the constraint level among variables, such that the short XOR constraints can reach the same reduction effect on solution space as the long ones. It improves the quality of XOR constraints as well as the SAT solving efficiency. Experimentally, we demonstrate that in almost every benchmark used in well-known ApproxMC2 and STAC_CNF, our approach outperforms the existing approximate model counters in both accuracy and efficiency.

Web services provide a general basis of convenient access and operation for cloud applications. However, such services become very vulnerable when being attacked, especially in the situation where service continuity is one of the most important requirements. This issue highlights the necessity to apply reliable and formal methods to attack tolerance in Web services. In this paper, we propose a Coloured Petri Nets based method for attack tolerance by modelling and analysing basic behaviours of attack-network interaction, attack detectors and their tolerance solutions. Furthermore, complex attacks can be analysed and tolerance solutions deployed by identifying these basic attack-network interactions and composing their solutions. The validity of our method is demonstrated through a case study on attack tolerance in cloud-based medical information storage.