TY - GEN
T1 - Parameterized weighted containment
AU - Avni, Guy
AU - Kupferman, Orna
PY - 2013
Y1 - 2013
N2 - Partially-specified systems and specifications are used in formal methods such as stepwise design and query checking. Existing methods consider a setting in which the systems and their correctness are Boolean. In recent years there has been growing interest and need for quantitative formal methods, where systems may be weighted and specifications may be multi valued. Weighted automata, which map input words to a numerical value, play a key role in quantitative reasoning. Technically, every transition in a weighted automaton A has a cost, and the value A assigns to a finite word w is the sum of the costs on the transitions participating in the most expensive accepting run of on w. We study parameterized weighted containment: given three weighted automata A, B, and C, with B being partial, the goal is to find an assignment to the missing costs in B so that we end up with B′ for which A ≤ B′ ≤ C, where ≤ is the weighted counterpart of containment. We also consider a one-sided version of the problem, where only A or only C are given in addition to B, and the goal is to find a minimal assignment with which A ≤ B′ or, respectively, a maximal one with which B′ ≤ C. We argue that both problems are useful in stepwise design of weighted systems as well as approximated minimization of weighted automata. We show that when the automata are deterministic, we can solve the problems in polynomial time. Our solution is based on the observation that the set of legal assignments to k missing costs forms a k-dimensional polytope. The technical challenge is to find an assignment in polynomial time even though the polytope is defined by means of exponentially many inequalities. We do so by using a powerful mathematical tool that enables us to develop a divide-and-conquer algorithm based on a separation oracle for polytopes. For nondeterministic automata, the weighted setting is much more complex, and in fact even non-parameterized containment is undecidable. We are still able to study variants of the problems, where containment is replaced by simulation.
AB - Partially-specified systems and specifications are used in formal methods such as stepwise design and query checking. Existing methods consider a setting in which the systems and their correctness are Boolean. In recent years there has been growing interest and need for quantitative formal methods, where systems may be weighted and specifications may be multi valued. Weighted automata, which map input words to a numerical value, play a key role in quantitative reasoning. Technically, every transition in a weighted automaton A has a cost, and the value A assigns to a finite word w is the sum of the costs on the transitions participating in the most expensive accepting run of on w. We study parameterized weighted containment: given three weighted automata A, B, and C, with B being partial, the goal is to find an assignment to the missing costs in B so that we end up with B′ for which A ≤ B′ ≤ C, where ≤ is the weighted counterpart of containment. We also consider a one-sided version of the problem, where only A or only C are given in addition to B, and the goal is to find a minimal assignment with which A ≤ B′ or, respectively, a maximal one with which B′ ≤ C. We argue that both problems are useful in stepwise design of weighted systems as well as approximated minimization of weighted automata. We show that when the automata are deterministic, we can solve the problems in polynomial time. Our solution is based on the observation that the set of legal assignments to k missing costs forms a k-dimensional polytope. The technical challenge is to find an assignment in polynomial time even though the polytope is defined by means of exponentially many inequalities. We do so by using a powerful mathematical tool that enables us to develop a divide-and-conquer algorithm based on a separation oracle for polytopes. For nondeterministic automata, the weighted setting is much more complex, and in fact even non-parameterized containment is undecidable. We are still able to study variants of the problems, where containment is replaced by simulation.
UR - http://www.scopus.com/inward/record.url?scp=84874447729&partnerID=8YFLogxK
U2 - 10.1007/978-3-642-37075-5_24
DO - 10.1007/978-3-642-37075-5_24
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AN - SCOPUS:84874447729
SN - 9783642370748
T3 - Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
SP - 369
EP - 384
BT - Foundations of Software Science and Computation Structures - 16th Int. Conference, FOSSACS 2013, Held as Part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2013, Proc.
T2 - 16th International Conference on Foundations of Software Science and Computation Structures, FOSSACS 2013, Held as Part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2013
Y2 - 16 March 2013 through 24 March 2013
ER -