Analyzing Satisfiability and Refutability in Selected Constraint Systems

This dissertation is concerned with the satisfiability and refutability problems for several constraint systems. We examine both Boolean constraint systems, in which each variable is limited to the values true and false, and polyhedral constraint systems, in which each variable is limited to the set of real numbers R in the case of linear polyhedral systems or the set of integers Z in the case of integer polyhedral systems. An important aspect of our research is that we focus on providing certificates. That is, we provide satisfying assignments or easily checkable proofs of infeasibility depending on whether the instance is feasible or not. Providing easily checkable certificates has become a much sought after feature in algorithms, especially in light of spectacular failures in the implementations of some well-known algorithms. There exist a number of problems in the constraint-solving domain for which efficient algorithms have been proposed, but which lack a certifying counterpart. When examining Boolean constraint systems, we specifically look at systems of 2-CNF clauses and systems of Horn clauses. When examining polyhedral constraint systems, we specifically look at systems of difference constraints, systems of UTVPI constraints, and systems of Horn constraints. For each examined system, we determine several properties of general refutations and determine the complexity of finding restricted refutations. These restricted forms of refutation include read-once refutations, in which each constraint can be used at most once; literal-once refutations, in which for each literal at most one constraint containing that literal can be used; and unit refutations, in which each step of the refutation must use a constraint containing exactly one literal. The advantage of read-once refutations is that they are guaranteed to be short. Thus, while not every constraint system has a read-once refutation, the small size of the refutation guarantees easy checkability

Efficient Generation of Craig Interpolants in Satisfiability Modulo Theories

The problem of computing Craig Interpolants has recently received a lot of interest. In this paper, we address the problem of efficient generation of interpolants for some important fragments of first order logic, which are amenable for effective decision procedures, called Satisfiability Modulo Theory solvers. We make the following contributions. First, we provide interpolation procedures for several basic theories of interest: the theories of linear arithmetic over the rationals, difference logic over rationals and integers, and UTVPI over rationals and integers. Second, we define a novel approach to interpolate combinations of theories, that applies to the Delayed Theory Combination approach. Efficiency is ensured by the fact that the proposed interpolation algorithms extend state of the art algorithms for Satisfiability Modulo Theories. Our experimental evaluation shows that the MathSAT SMT solver can produce interpolants with minor overhead in search, and much more efficiently than other competitor solvers.Comment: submitted to ACM Transactions on Computational Logic (TOCL

Managing Complex Scheduling Problems with Dynamic and Hybrid Constraints.

The task of scheduling can often be a difficult one because of the inherent complexity of real-world problems. In the field of Artificial Intelligence, many representations and algorithms have been developed to automate the scheduling process. Many state of the art scheduling systems deal with this complexity by making assumptions that simplify the algorithms, but in doing so, miss some opportunities to improve performance. Scheduling problems are temporal in nature, and so they often contain constraints that change over time. Many scheduling systems assume that the problems they are solving are all independent, and so they ignore the similarities between subsequent sets of scheduling constraints. Additionally, scheduling problems often contain a mixture of finite-domain and temporal constraints. Many of the systems that can solve problems of this type do so by creating finite-domain variables to represent the constraints, but then ignore the distinction between the different types of variables when searching for a solution. In this dissertation, I identify opportunities to improve performance by exploiting structure where it has previously been overlooked. Following this approach, I develop a set of techniques that apply to a wide variety of situations that can arise in real-world scheduling problems. First, I consider dynamic scheduling problems with constraints that change over time. To address such problems, I introduce a new representation called the Dynamic Disjunctive Temporal Problem, along with several techniques to improve both efficiency and stability when solving one. Second, I consider scheduling problems in which a mixture of finite-domain and temporal variables can interact through hybrid constraints. I introduce the Hybrid Scheduling Problem to represent such problems, and I present a set of techniques that capitalize on the distinction between variable types to improve efficiency across the problem space. Finally, I conclude by proposing several ways that the dynamic and hybrid representations and techniques can be combined. To compare many of the techniques presented throughout this dissertation in the context of structured, real-world problems, I use them to solve scheduling problems based on actual air traffic control constraints recorded from the Dallas/Fort Worth International Airport.Ph.D.Computer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/57625/2/pschwart_1.pd

Lossless Selection Views under Constraints

The problem of updating a database through a set of views consists in propagat-ing updates of the views to the base relations over which the view relations are defined, so that the changes to the database reflect exactly those to the views. This is a classical problem in database research, known as the view update prob

МЕТОДЫ ПОИСКА НЕСКОЛЬКИХ РЕШЕНИЙ СИСТЕМЫ РАЗНОСТНЫХ И ИНТЕРВАЛЬНЫХ ОГРАНИЧЕНИЙ

We develop two methods of solving DBM system. One method is based on Fourier – Motskinelimination scheme, it has complexity O(n3) for finding initial solve and complexity O(n3) for finding solve by changing one of variable value for some cases. The other method is based on the network of constraints approach, it has complexity O(n3) for finding initial solve and  O(n) or approximately for finding solve by changing one of variable value if it is limited by special bounds.  Рассматриваются методы поиска решений систем линейных неравенств специального вида, состоящих из разностных неравенств с двумя переменными и интервальных ограничений с одной переменной. Для решения таких систем предлагаются два подхода, с помощью которых могут быть найдены два экстремальных («максимальное» и «минимальное») решения, а также некоторые другие решения. Первый подход основан на методе Фурье – Моцкина, второй – на представлении системы в виде сети ограничений

Проблема проверки выполнимости формул разрешимых теорий (обзор)

Данная работа посвящена анализу современного состояния исследований проблемы проверки выполнимости формул разрешимых теорий 1-го порядка на основе ѕленивого подходаї, т.е. на интеграции SAT-решателей с T -решателями. Охарактеризована структура SAT-решателя, построенного на основе управляющей конфликтами DPLL-процедуре. Рассмотрены основные понятия и принципы, используемые в процессе построения современных T -решателей. Изложение иллюстрируется на примере решателя, предназначенного для анализа выполнимости формул линейной целочисленной арифметики. Охарактеризованы методы организации взаимодействия SAT-решателей и T -решателей.Дану статтю присв’ячено аналiзу сучасного стану дослiджень проблеми перевiрки здiйсненостi формул теорiй 1-го порядку на основi ѕледащого пiдходуї, тобто на iнтеграцiї SAT-вирiшувачiв з T -вирiшувачами. Охарактеризовано структуру SAT-вирiшувача, який побудовано на основi керуючою конфлiктами DPLL-процедури. Розглянуто основнi поняття та принципи, якi використуються при побудовi сучасних T -вирiшувачiв. Викладення iлюструється на прикладi вирiшувача, який призначено для перевiрки здiйсненостi формул лiнiйної арифметики цiлих чисел. Охарактеризовано методи iнтеграцiї SAT-вирiшувачiв з T -вирiшувачами.Given paper is devoted to analysis of the state of the art for investigations of the problem of checking for satisfiability of formulae in decidable first-order theories on the base of the lazy approach, i.e. on integration of SAT-solvers with T -solvers. The structure of SAT-solver designed on the base of conflict driven DPLL procedure is characterized. Basic notions and principles applied in the process of elaboration of modern T -solvers are considered. They are presented in detail for example of a solver intended for checking of satisfiability for formulae of linear integer arithmetic. Methods of integration of SAT-solvers with T -solvers are characterized