Results 1  10
of
103
Efficient Static Analysis of XML Paths and Types
, 2008
"... We present an algorithm to solve XPath decision problems under regular tree type constraints and show its use to statically typecheck XPath queries. To this end, we prove the decidability of a logic with converse for finite ordered trees whose time complexity is a simple exponential of the size of ..."
Abstract

Cited by 60 (33 self)
 Add to MetaCart
We present an algorithm to solve XPath decision problems under regular tree type constraints and show its use to statically typecheck XPath queries. To this end, we prove the decidability of a logic with converse for finite ordered trees whose time complexity is a simple exponential of the size of a formula. The logic corresponds to the alternation free modal µcalculus without greatest fixpoint, restricted to finite trees, and where formulas are cyclefree. Our proof method is based on two auxiliary results. First, XML regular tree types and XPath expressions have a linear translation to cyclefree formulas. Second, the least and greatest fixpoints are equivalent for finite trees, hence the logic is closed under negation. Building on these results, we describe a practical, effective system for solving the satisfiability of a formula. The system has been experimented with some decision problems such as XPath emptiness, containment, overlap, and coverage, with or without type constraints. The benefit of the approach is that our system can be effectively used in static analyzers for programming languages
Reasoning in expressive description logics with fixpoints based on automata on infinite trees
 In Proc. of the 16th Int. Joint Conf. on Artificial Intelligence (IJCAI’99
, 1999
"... In the last years, the investigation on Description Logics (DLs) has been driven by the goal of applying them in several areas, such as, software engineering, information systems, databases, information integration, and intelligent access to the web. The modeling requirements arising in the above ar ..."
Abstract

Cited by 55 (12 self)
 Add to MetaCart
In the last years, the investigation on Description Logics (DLs) has been driven by the goal of applying them in several areas, such as, software engineering, information systems, databases, information integration, and intelligent access to the web. The modeling requirements arising in the above areas have stimulated the need for very rich languages, including fixpoint constructs to represent recursive structures. We study a DL comprising the most general form of fixpoint constructs on concepts, all classical concept forming constructs, plus inverse roles, nary relations, qualified number restrictions, and inclusion assertions. We establish the EXPTIME decidability of such logic by presenting a decision procedure based on a reduction to nonemptiness of alternating automata on infinite trees. We observe that this is the first decidability result for a logic combining inverse roles, number restrictions, and general fixpoints. 1
From nondeterministic Büchi and Streett automata to deterministic parity automata
 In 21st Symposium on Logic in Computer Science (LICS’06
, 2006
"... Determinization and complementation are fundamental notions in computer science. When considering finite automata on finite words determinization gives also a solution to complementation. Given a nondeterministic finite automaton there exists an exponential construction that gives a deterministic au ..."
Abstract

Cited by 45 (3 self)
 Add to MetaCart
Determinization and complementation are fundamental notions in computer science. When considering finite automata on finite words determinization gives also a solution to complementation. Given a nondeterministic finite automaton there exists an exponential construction that gives a deterministic automaton for the same language. Dualizing the set of accepting states gives an automaton for the complement language. In the theory of automata on infinite words, determinization and complementation are much more involved. Safra provides determinization constructions for Büchi and Streett automata that result in deterministic Rabin automata. For a Büchi automaton with n states, Safra constructs a deterministic Rabin automaton with n O(n) states and n pairs. For a Streett automaton with n states and k pairs, Safra constructs a deterministic Rabin automaton with (nk) O(nk) states and n(k + 1) pairs. Here, we reconsider Safra’s determinization constructions. We show how to construct automata with fewer states and, most importantly, parity acceptance condition. Specifically, starting from a nondeterministic Büchi automaton with n states our construction yields a deterministic parity automaton with n 2n+2 states and index 2n (instead of a Rabin automaton with (12) n n 2n states and n pairs). Starting from a nondeterministic Streett automaton with n states and k pairs our construction yields a deterministic parity automaton with n n(k+2)+2 (k+1) 2n(k+1) states and index 2n(k + 1) (instead of a Rabin automaton with (12) n(k+1) n n(k+2) (k+1) 2n(k+1) states and n(k+1) pairs). The parity condition is much simpler than the Rabin condition. In applications such as solving games and emptiness of tree automata handling the Rabin condition involves an additional multiplier of n 2 n! (or (n(k + 1)) 2 (n(k + 1))! in the case of Streett) which is saved using our construction.
Answering regular path queries in expressive description logics: An automatatheoretic approach
 In Proc. of the 22nd Nat. Conf. on Artificial Intelligence (AAAI 2007
, 2007
"... Expressive Description Logics (DLs) have been advocated as formalisms for modeling the domain of interest in various application areas. An important requirement is the ability to answer complex queries beyond instance retrieval, taking into account constraints expressed in a knowledge base. We consi ..."
Abstract

Cited by 35 (17 self)
 Add to MetaCart
Expressive Description Logics (DLs) have been advocated as formalisms for modeling the domain of interest in various application areas. An important requirement is the ability to answer complex queries beyond instance retrieval, taking into account constraints expressed in a knowledge base. We consider this task for positive existential path queries (which generalize conjunctive queries and unions thereof), whose atoms are regular expressions over the roles (and concepts) of a knowledge base in the expressive DL ALCQIbreg. Using techniques based on twoway treeautomata, we first provide an elegant characterization of TBox and ABox reasoning, which gives us also a tight EXPTIME bound. We then prove decidability (more precisely, a 2EXPTIME upper bound) of query answering, thus significantly pushing the decidability frontier, both with respect to the query language and the considered DL. We also show that query answering is EXPSPACEhard already in rather restricted settings.
From PreHistoric to PostModern Symbolic Model Checking
 In Proceedings of the International Conference on ComputerAided Veri
, 1998
"... Abstract. Symbolic model checking, which enables the automatic verification of large systems, proceeds by calculating with expressions that represent state sets. Traditionally, symbolic modelchecking tools are based on backward state traversal; their basic operation is the function £¥¤§ ¦ , which g ..."
Abstract

Cited by 33 (5 self)
 Add to MetaCart
Abstract. Symbolic model checking, which enables the automatic verification of large systems, proceeds by calculating with expressions that represent state sets. Traditionally, symbolic modelchecking tools are based on backward state traversal; their basic operation is the function £¥¤§ ¦ , which given a set of states, returns the set of all predecessor states. This is because specifiers usually employ formalisms with futuretime modalities, which are naturally evaluated by iterating applications of £¨¤§ ¦. It has been recently shown experimentally that symbolic model checking can perform significantly better if it is based, instead, on forward state traversal; in this case, the basic operation is the function £�©��§ � , which given a set of states, returns the set of all successor states. This is because forward state traversal can ensure that only those parts of the state space are explored which are reachable from an initial state and relevant for satisfaction or violation of the specification; that is, errors can be detected as soon as possible. In this paper, we investigate which specifications can be checked by symbolic forward state traversal. We formulate the problems of symbolic backward and forward model checking by means of two �calculi. The �¥�� � � calculus is based on the £¨¤� ¦ operation; the �¨���� �� calculus, on the £�©��§ � operation. These two �calculi induce query logics, which augment fixpoint expressions with a boolean emptiness query. Using query logics, we are able to relate and compare the symbolic backward and forward approaches. In particular, we prove that all �regular (lineartime) specifications can be expressed as�¨���� � � queries, and therefore checked using symbolic forward state traversal. On the other hand, we show that there are simple branchingtime specifications that cannot be checked in this way. 1
An automatatheoretic approach to reasoning about infinitestate systems
 LNCS
, 2000
"... Abstract. We develop an automatatheoretic framework for reasoning about infinitestate sequential systems. Our framework is based on the observation that states of such systems, which carry a finite but unbounded amount of information, can be viewed as nodes in an infinite tree, and transitions betw ..."
Abstract

Cited by 33 (4 self)
 Add to MetaCart
Abstract. We develop an automatatheoretic framework for reasoning about infinitestate sequential systems. Our framework is based on the observation that states of such systems, which carry a finite but unbounded amount of information, can be viewed as nodes in an infinite tree, and transitions between states can be simulated by finitestate automata. Checking that the system satisfies a temporal property can then be done by an alternating twoway tree automaton that navigates through the tree. As has been the case with finitestate systems, the automatatheoretic framework is quite versatile. We demonstrate it by solving several versions of the modelchecking problem for §calculus specifications and prefixrecognizable systems, and by solving the realizability and synthesis problems for §calculus specifications with respect to prefixrecognizable environments. 1
Logics for unranked trees: an overview
 Logical Methods in Computer Science 2, Issue 3, Paper 2
, 2006
"... Vol. 2 (3:2) 2006, pp. 1–31 www.lmcsonline.org ..."
Ontologies and databases: The DLLite approach
 In Reasoning Web, volume 5689 of LNCS
, 2009
"... Abstract. Ontologies provide a conceptualization of a domain of interest. Nowadays, they are typically represented in terms of Description Logics (DLs), and are seen as the key technology used to describe the semantics of information at various sites. The idea of using ontologies as a conceptual vie ..."
Abstract

Cited by 26 (17 self)
 Add to MetaCart
Abstract. Ontologies provide a conceptualization of a domain of interest. Nowadays, they are typically represented in terms of Description Logics (DLs), and are seen as the key technology used to describe the semantics of information at various sites. The idea of using ontologies as a conceptual view over data repositories is becoming more and more popular, but for it to become widespread in standard applications, it is fundamental that the conceptual layer through which the underlying data layer is accessed does not introduce a significant overhead in dealing with the data. Based on these observations, in recent years a family of DLs, called DLLite, has been proposed, which is specifically tailored to capture basic ontology and conceptual data modeling languages, while keeping low complexity of reasoning and of answering complex queries, in particular when the complexity is measured w.r.t. the size of the data. In this article, we present a detailed account of the major results that have been achieved for the DLLite family. Specifically, we concentrate on DLLiteA,id, an expressive member of this family, present algorithms for reasoning and query answering over DLLiteA,id ontologies,