SAT Encodings of Finite CSPs

Boolean satisfiability (SAT) is the problem of determining whether there exists an assignment of the Boolean variables to the truth values such that a given Boolean formula evaluates to true. SAT was the first example of an NP-complete problem [Coo71]. Only two decades ago SAT was mainly considered as of a theoretical interest. Nowadays, the picture is very different. SAT solving becomes mature and is a successful approach for tackling a large number of applications, ranging from artificial intelligence to industrial hardware design and verification. SAT solving consists of encodings and solvers. In order to benefit from the tremendous advances in the development of solvers, one must first encode the original problems into SAT instances. These encodings should not only be easily generated, but should also be efficiently processed by SAT solvers. Furthermore, an increasing number of practical applications in computer science can be expressed as constraint satisfaction problems (CSPs). However, encoding a CSP to SAT is currently regarded as more of an art than a science, and choosing an appropriate encoding is considered as important as choosing an algorithm. Moreover, it is much easier and more efficient to benefit from highly optimized state-of-the-art SAT solvers than to develop specialized tools from scratch. Hence, finding appropriate SAT encodings of CSPs is one of the most fascinating challenges for solving problems by SAT. This thesis studies SAT encodings of CSPs and aims at: 1) conducting a comprehensively profound study of SAT encodings of CSPs by separately investigating encodings of CSP domains and constraints; 2) proposing new SAT encodings of CSP domains; 3) proposing new SAT encoding of the at-most-one constraint, which is essential for encoding CSP variables; 4) introducing the redundant encoding and the hybrid encoding that aim to benefit from both two efficient and common SAT encodings (i.e., the sparse and order encodings) by using the channeling constraint (a term used in Constraint Programming) for SAT; and 5) revealing interesting guidelines on how to choose an appropriate SAT encoding in the way that one can exploit the availability of many efficient SAT solvers to solve CSPs efficiently and effectively. Experiments show that the proposed encodings and guidelines improve the state-of-the-art SAT encodings of CSPs.