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Twovariable logic on data trees and XML reasoning
"... Motivated by reasoning tasks for XML languages, the satisfiability problem of logics on data trees is investigated. The nodes of a data tree have a label from a finite set and a data value from a possibly infinite set. It is shown that satisfiability for twovariable firstorder logic is decidable i ..."
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Cited by 84 (17 self)
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Motivated by reasoning tasks for XML languages, the satisfiability problem of logics on data trees is investigated. The nodes of a data tree have a label from a finite set and a data value from a possibly infinite set. It is shown that satisfiability for twovariable firstorder logic is decidable if the tree structure can be accessed only through the child and the next sibling predicates and the access to data values is restricted to equality tests. From this main result, decidability of satisfiability and containment for a dataaware fragment of XPath and of the implication problem for unary key and inclusion constraints is concluded.
LTL with the freeze quantifier and register automata
 In LICS’06
, 2006
"... Temporal logics, firstorder logics, and automata over data words have recently attracted considerable attention. A data word is a word over a finite alphabet, together with a datum (an element of an infinite domain) at each position. Examples include timed words and XML documents. To refer to the d ..."
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Cited by 75 (7 self)
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Temporal logics, firstorder logics, and automata over data words have recently attracted considerable attention. A data word is a word over a finite alphabet, together with a datum (an element of an infinite domain) at each position. Examples include timed words and XML documents. To refer to the data, temporal logics are extended with the freeze quantifier, firstorder logics with predicates over the data domain, and automata with registers or pebbles. We investigate relative expressiveness and complexity of standard decision problems for LTL with the freeze quantifier (LTL ↓), 2variable firstorder logic (FO 2) over data words, and register automata. The only predicate available on data is equality. Previously undiscovered connections among those formalisms, and to counter automata with incrementing errors, enable us to answer several questions left open in recent literature. We show that the futuretime fragment of LTL ↓ which corresponds to FO 2 over finite data words can be extended considerably while preserving decidability, but at the expense of nonprimitive recursive complexity, and that most of further extensions are undecidable. We also prove that surprisingly, over infinite data words, LTL ↓ without the ‘until’ operator, as well as nonemptiness of oneway universal register automata, are undecidable even when there is only 1 register. 1.
Verification of relational datacentric dynamic systems with external services
, 2013
"... Datacentric dynamic systems are systems where both the process controlling the dynamics and the manipulation of data are equally central. We study verification of (firstorder) µcalculus variants over relational datacentric dynamic systems, where data are maintained in a relational database, and ..."
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Cited by 51 (20 self)
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Datacentric dynamic systems are systems where both the process controlling the dynamics and the manipulation of data are equally central. We study verification of (firstorder) µcalculus variants over relational datacentric dynamic systems, where data are maintained in a relational database, and the process is described in terms of atomic actions that evolve the database. Action execution may involve calls to external services, thus inserting fresh data into the system. As a result such systems are infinitestate. We show that verification is undecidable in general, and we isolate notable cases where decidability is achieved. Specifically we start by considering service calls that return values deterministically (depending only on passed parameters). We show that in a µcalculus variant that preserves knowledge of objects appeared along a run we get decidability under the assumption that the fresh data introduced along a
LOGICS FOR UNRANKED TREES: AN OVERVIEW
 CONSIDERED FOR PUBLICATION IN LOGICAL METHODS IN COMPUTER SCIENCE
, 2006
"... Labeled unranked trees are used as a model of XML documents, and logical languages for them have been studied actively over the past several years. Such logics have different purposes: some are better suited for extracting data, some for expressing navigational properties, and some make it easy to ..."
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Cited by 37 (6 self)
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Labeled unranked trees are used as a model of XML documents, and logical languages for them have been studied actively over the past several years. Such logics have different purposes: some are better suited for extracting data, some for expressing navigational properties, and some make it easy to relate complex properties of trees to the existence of tree automata for those properties. Furthermore, logics differ significantly in their modelchecking properties, their automata models, and their behavior on ordered and unordered trees. In this paper we present a survey of logics for unranked trees.
Static analysis of Active XML systems
 in PODS, 2008
"... Active XML is a highlevel specification language tailored to dataintensive, distributed, dynamic Web services. Active XML is based on XML documents with embedded function calls. The state of a document evolves depending on the result of internal function calls (local computations) or external ones ..."
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Cited by 35 (15 self)
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Active XML is a highlevel specification language tailored to dataintensive, distributed, dynamic Web services. Active XML is based on XML documents with embedded function calls. The state of a document evolves depending on the result of internal function calls (local computations) or external ones (interactions with users or other services). Function calls return documents that may be active, so may activate new subtasks. The focus of the paper is on the verification of temporal properties of runs of Active XML systems, specified in a treepattern based temporal logic, TreeLTL, that allows expressing a rich class of semantic properties of the application. The main results establish the boundary of decidability and the complexity of automatic verification of TreeLTL properties. 1
Twovariable logic on data words
, 2007
"... In a data word each position carries a label from a finite alphabet and a data value from some infinite domain. These models have been already considered in the realm of semistructured data, timed automata and extended temporal logics. It is shown that satisfiability for the twovariable firstorder ..."
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Cited by 35 (4 self)
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In a data word each position carries a label from a finite alphabet and a data value from some infinite domain. These models have been already considered in the realm of semistructured data, timed automata and extended temporal logics. It is shown that satisfiability for the twovariable firstorder logic FO 2 (∼,<,+1) is decidable over finite and over infinite data words, where ∼ is a binary predicate testing the data value equality and +1, < are the usual successor and order predicates. The complexity of the problem is at least as hard as Petri net reachability. Several extensions of the logic are considered, some remain decidable while some are undecidable.
Automata with group actions
 In LICS
, 2011
"... Abstract—Our motivating question is a MyhillNerode theorem for infinite alphabets. We consider several kinds of those: alphabets whose letters can be compared only for equality, but also ones with more structure, such as a total order or a partial order. We develop a framework for studying such alp ..."
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Cited by 33 (8 self)
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Abstract—Our motivating question is a MyhillNerode theorem for infinite alphabets. We consider several kinds of those: alphabets whose letters can be compared only for equality, but also ones with more structure, such as a total order or a partial order. We develop a framework for studying such alphabets, where the key role is played by the automorphism group of the alphabet. This framework builds on the idea of nominal sets of Gabbay and Pitts; nominal sets are the special case of our framework where letters can be only compared for equality. We use the framework to uniformly generalize to infinite alphabets parts of automata theory, including decidability results. In the case of letters compared for equality, we obtain automata equivalent in expressive power to finite memory automata, as defined by Francez and Kaminski. I.
Streaming transducers for algorithmic verification of singlepass listprocessing programs
 In 38th ACM SIGACTSIGPLAN Symposium on Princples of Programming Languages (POPL’11
, 2011
"... We introduce streaming data string transducers that map input data strings to output data strings in a single lefttoright pass in linear time. Data strings are (unbounded) sequences of data values, tagged with symbols from a finite set, over a potentially infinite data domain that supports only th ..."
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Cited by 33 (8 self)
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We introduce streaming data string transducers that map input data strings to output data strings in a single lefttoright pass in linear time. Data strings are (unbounded) sequences of data values, tagged with symbols from a finite set, over a potentially infinite data domain that supports only the operations of equality and ordering. The transducer uses a finite set of states, a finite set of variables ranging over the data domain, and a finite set of variables ranging over data strings. At every step, it can make decisions based on the next input symbol, updating its state, remembering the input data value in its data variables, and updating datastring variables by concatenating datastring variables and new symbols formed from data variables, while avoiding duplication. We establish that the problems of checking functional equivalence of two streaming transducers, and of checking whether a streaming transducer satisfies pre/post
On notions of regularity for data languages
 In FCT
, 2007
"... Motivated by considerations in XML database theory and model checking, data strings have been introduced as an extension of finite alphabet strings which carry, at each position, a symbol and a data value from an infinite domain. Previous work has shown that it is difficult to come up with an expres ..."
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Cited by 28 (5 self)
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Motivated by considerations in XML database theory and model checking, data strings have been introduced as an extension of finite alphabet strings which carry, at each position, a symbol and a data value from an infinite domain. Previous work has shown that it is difficult to come up with an expressive yet decidable automaton model for data languages. Recently, such a model, data automata, was introduced. This paper introduces a simpler but equivalent model and investigates its expressive power, algorithmic and closure properties, and some extensions. 1