Results 1  10
of
39
Reasoning about Infinite Computations
 Information and Computation
, 1994
"... We investigate extensions of temporal logic by connectives defined by finite automata on infinite words. We consider three different logics, corresponding to three different types of acceptance conditions (finite, looping and repeating) for the automata. It turns out, however, that these logics all ..."
Abstract

Cited by 250 (55 self)
 Add to MetaCart
We investigate extensions of temporal logic by connectives defined by finite automata on infinite words. We consider three different logics, corresponding to three different types of acceptance conditions (finite, looping and repeating) for the automata. It turns out, however, that these logics all have the same expressive power and that their decision problems are all PSPACEcomplete. We also investigate connectives defined by alternating automata and show that they do not increase the expressive power of the logic or the complexity of the decision problem. 1 Introduction For many years, logics of programs have been tools for reasoning about the input/output behavior of programs. When dealing with concurrent or nonterminating processes (like operating systems) there is, however, a need to reason about infinite computations. Thus, instead of considering the first and last states of finite computations, we need to consider the infinite sequences of states that the program goes through...
Ontology Reasoning in the SHOQ(D) Description Logic
 In Proc. of the 17th Int. Joint Conf. on Artificial Intelligence (IJCAI 2001
, 2001
"... Ontologies are set to play a key role in the "Semantic Web" by providing a source of shared and precisely defined terms that can be used in descriptions of web resources. Reasoning over such descriptions will be essential if web resources are to be more accessible to automated processes. SHOQ ..."
Abstract

Cited by 135 (34 self)
 Add to MetaCart
Ontologies are set to play a key role in the "Semantic Web" by providing a source of shared and precisely defined terms that can be used in descriptions of web resources. Reasoning over such descriptions will be essential if web resources are to be more accessible to automated processes. SHOQ(D) is an expressive description logic equipped with named individuals and concrete datatypes which has almost exactly the same expressive power as the latest web ontology languages (e.g., OIL and DAML). We present sound and complete reasoning services for this logic. 1
Structured objects: Modeling and reasoning
 Proc. of DOOD95
, 1995
"... Abstract. One distinctive characteristic of objectoriented data models over traditional database systems is that they provide more expressive power in schema de nition. Nevertheless, the de ning power of objectoriented models is still somewhat limited, mainly because it is commonly accepted that pa ..."
Abstract

Cited by 51 (34 self)
 Add to MetaCart
Abstract. One distinctive characteristic of objectoriented data models over traditional database systems is that they provide more expressive power in schema de nition. Nevertheless, the de ning power of objectoriented models is still somewhat limited, mainly because it is commonly accepted that part of the semantics of the application can be represented within methods. The research work reported in this paper explores the possibility of enhancing the power of objectoriented data models in schema de nition, thus o ering more possibilities to reason about the intension of the database and better supporting data management. We demonstrate our approach by presenting a new data model, called CVL, that extends the usual objectoriented data models with several aspects, including view de nition, recursive structure modeling, navigation of the schema through forward and backward traversal of links (attributes and relations), subsetting of attributes, and cardinality ratio constraints on links. CVL is equipped with sound, complete, and terminating inference procedures, that allow various forms of reasoning to be carried out on the intensional level of the database. 1
An algorithm for strongly connected component analysis in n log n symbolic steps
 Formal Methods in System Design
"... Abstract. We present a symbolic algorithm for strongly connected component decomposition. The algorithm performs �(n log n) image and preimage computations in the worst case, where n is the number of nodes in the graph. This is an improvement over the previously known quadratic bound. The algorithm ..."
Abstract

Cited by 47 (6 self)
 Add to MetaCart
Abstract. We present a symbolic algorithm for strongly connected component decomposition. The algorithm performs �(n log n) image and preimage computations in the worst case, where n is the number of nodes in the graph. This is an improvement over the previously known quadratic bound. The algorithm can be used to decide emptiness of Büchi automata with the same complexity bound, improving Emerson and Lei’s quadratic bound, and emptiness of Streett automata, with a similar bound in terms of nodes. It also leads to an improved procedure for the generation of nonemptiness witnesses.
ModelChecking of Causality Properties
, 1995
"... A temporal logic for causality (Tlc) is introduced. The logic is interpreted over causal structures corresponding to partial order executions of programs. For causal structures describing the behavior of a finite fixed set of processes, a Tlcformula can, equivalently, be interpreted over their line ..."
Abstract

Cited by 43 (10 self)
 Add to MetaCart
A temporal logic for causality (Tlc) is introduced. The logic is interpreted over causal structures corresponding to partial order executions of programs. For causal structures describing the behavior of a finite fixed set of processes, a Tlcformula can, equivalently, be interpreted over their linearizations. The main result of the paper is a tableau construction that gives a singlyexponential translation from a Tlc formula ' to a Streett automaton that accepts the set of linearizations satisfying '. This allows both checking the validity of Tlc formulas and modelchecking of program properties. As the logic Tlc does not distinguish among different linearizations of the same partial order execution, partial order reduction techniques can be applied to alleviate the statespace explosion problem of modelchecking. 1 Introduction One of the most successful techniques for automatic verification of finitestate systems has been modelchecking . A modelchecking algorithm decides wheth...
Distributed Explicit Fair Cycle Detection (Set Based Approach)
"... The fair cycle detectiou problem is at the heart of both LTL and fair CTL model checking. This paper preseuts a new distributed scalable algorithm for explicit fair cycle detection. Our method combines the simplicity of the distributiou of explicitly preseuted data structure and the features of ..."
Abstract

Cited by 41 (12 self)
 Add to MetaCart
The fair cycle detectiou problem is at the heart of both LTL and fair CTL model checking. This paper preseuts a new distributed scalable algorithm for explicit fair cycle detection. Our method combines the simplicity of the distributiou of explicitly preseuted data structure and the features of symbolic algorithm allowing for an efficient parallelisa tion. If a fair cycle (i.e. couuterexample) is detected, theu the algorithm produces a cycle, which is in general shorter than that produced by depthfirst search based algorithms, Experimental results confirm that our approach outperforms that based ou a direct implementation of the best sequential algorithm.
Complexity of Automata on Infinite Objects
, 1989
"... We investigate in this thesis problems concerning the complexity of translation among, and decision procedure for, different types of finite automata on infinite words (! automata). An !automaton is the same as usual finite automata over finite strings but it accepts or rejects infinite strings. I ..."
Abstract

Cited by 38 (0 self)
 Add to MetaCart
We investigate in this thesis problems concerning the complexity of translation among, and decision procedure for, different types of finite automata on infinite words (! automata). An !automaton is the same as usual finite automata over finite strings but it accepts or rejects infinite strings. It may be either deterministic or nondeterministic, and may have different types of acceptance condition. Our main result is a new, simpler, determinization construction that yields a single exponent upper bound for the translation of any Buchi nondeterministic !automaton into a deterministic !auomaton. This construction is optimal. We also look at the complexity of the complementation problem for different types of !automata, and, among other results, obtain an exponential complementation for Streett !automata. These results can be used to improve the complexity of decision procedures for different logics that use automatatheoretic techniques. Acknowledgement First and foremost, I o...
Finite model reasoning in description logics
 In Proc. of the 5th Int. Conf. on the Principles of Knowledge Representation and Reasoning (KR96
, 1996
"... For the basic Description Logics reasoning with respect to finite models amounts to reasoning with respect to arbitrary ones, but finiteness of the domain needs to be considered if expressivity is increased and the finite model property fails. Procedures for reasoning with respect to arbitrary model ..."
Abstract

Cited by 37 (16 self)
 Add to MetaCart
For the basic Description Logics reasoning with respect to finite models amounts to reasoning with respect to arbitrary ones, but finiteness of the domain needs to be considered if expressivity is increased and the finite model property fails. Procedures for reasoning with respect to arbitrary models in very expressive Description Logics have been developed, but these are not directly applicable in the finite case. We first show that we can nevertheless capture a restricted form of finiteness and represent finite modeling structures such as lists and trees, while still reasoning with respect to arbitrary models. The main result of this paper is a procedure to reason with respect to finite models in an expressive Description Logic equipped with inverse roles, cardinality constraints, and in which arbitrary inclusions between concepts can be specified without any restriction. This provides the necessary expressivity to go beyond most semantic and objectoriented Database models, and capture several useful extensions. 1
Exponential Determinization for ωAutomata with StrongFairness Acceptance Condition
"... In [Saf88] an exponential determinization procedure for Buchi automata was shown, yielding tight bounds for decision procedures of some logics ([EJ88, Saf88, SV89, KT89]). In [SV89] the complexity of determinization and complementation of ωautomata was further investigated, leaving as an open q ..."
Abstract

Cited by 17 (0 self)
 Add to MetaCart
In [Saf88] an exponential determinization procedure for Buchi automata was shown, yielding tight bounds for decision procedures of some logics ([EJ88, Saf88, SV89, KT89]). In [SV89] the complexity of determinization and complementation of ωautomata was further investigated, leaving as an open question the complexity of the determinization of a single class of ωautomata. For this class of ωautomata with strong fairness as acceptance condition (Streett automata), [SV89] managed to show an exponential complementation procedure, however the blowup of translating these automata, to any of the classes known to admit exponential determinization, is inherently exponential. This might suggest that the blowup of the determinization of Streett automata is inherently doubly exponential. This paper shows an exponential determinization construction for Streett automata. In fact, the complexity of our construction is roughly the same as the complexity achieved in [Saf88] for Büchi ...