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235
Computing with Membranes
 JOURNAL OF COMPUTER AND SYSTEM SCIENCES
, 1998
"... We introduce a new computability model, of a distributed parallel type, based on the notion of a membrane structure. Such a structure consists of several celllike membranes, recurrently placed inside a unique "skin" membrane. A plane representation is a Venn diagram without intersected se ..."
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Cited by 425 (4 self)
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We introduce a new computability model, of a distributed parallel type, based on the notion of a membrane structure. Such a structure consists of several celllike membranes, recurrently placed inside a unique "skin" membrane. A plane representation is a Venn diagram without intersected sets and with a unique superset. In the regions delimited by the membranes there are placed objects; the obtained construct is called a supercell. These objects are assumed to evolve: each object can be transformed in other objects, can pas through a membrane, or can disolve the membrane in which it is placed. A priority relation between evolution rules can be considered. The evolution is done in parallel for all objects able to evolve. In this way, we obtain a computing device (we call it a supercell system): start with a certain number of objects in a certain membrane and let the system evolve; if it will halt (no object can further evolve), then the computation is finished, with the result given as...
Typechecking for XML Transformers
 IN PROCEEDINGS OF THE NINETEENTH ACM SIGMODSIGACTSIGART SYMPOSIUM ON PRINCIPLES OF DATABASE SYSTEMS
, 2000
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Processing XML Streams with deterministic automata
, 2003
"... Abstract. We consider the problem of evaluating a large number of XPath expressions on an XML stream. Our main contribution consists in showing that Deterministic Finite Automata (DFA) can be used effectively for this problem: in our experiments we achieve a throughput of about 5.4MB/s, independent ..."
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Cited by 159 (4 self)
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Abstract. We consider the problem of evaluating a large number of XPath expressions on an XML stream. Our main contribution consists in showing that Deterministic Finite Automata (DFA) can be used effectively for this problem: in our experiments we achieve a throughput of about 5.4MB/s, independent of the number of XPath expressions (up to 1,000,000 in our tests). The major problem we face is that of the size of the DFA. Since the number of states grows exponentially with the number of XPath expressions, it was previously believed that DFAs cannot be used to process large sets of expressions. We make a theoretical analysis of the number of states in the DFA resulting from XPath expressions, and consider both the case when it is constructed eagerly, and when it is constructed lazily. Our analysis indicates that, when the automaton is constructed lazily, and under certain assumptions about the structure of the input XML data, the number of states in the lazy DFA is manageable. We also validate experimentally our findings, on both synthetic and real XML data sets. 1
UnQL: A Query Language and Algebra for Semistructured Data Based on Structural Recursion
, 2000
"... This paper presents structural recursion as the basis of the syntax and semantics of query languages for semistructured data and XML. We describe a simple and powerful query language based on pattern matching and show that it can be expressed using structural recursion, which is introduced as a top ..."
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Cited by 138 (4 self)
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This paper presents structural recursion as the basis of the syntax and semantics of query languages for semistructured data and XML. We describe a simple and powerful query language based on pattern matching and show that it can be expressed using structural recursion, which is introduced as a topdown, recursive function, similar to the way XSL is defined on XML trees. On cyclic data, structural recursion can be defined in two equivalent ways: as a recursive function which evaluates the data topdown and remembers all its calls to avoid infinite loops, or as a bulk evaluation which processes the entire data in parallel using only traditional relational algebra operators. The latter makes it possible for optimization techniques in relational queries to be applied to structural recursion. We show that the composition of two structural recursion queries can be expressed as a single such query, and this is used as the basis of an optimization method for mediator systems. Several other fo...
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 ..."
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Cited by 63 (6 self)
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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.
Hybrid Logics
"... This chapter provides a modern overview of the field of hybrid logic. Hybrid logics are extensions of standard modal logics, involving symbols that name individual states in models. The first results that are nowadays considered as part of the field date back to the early work of Arthur ..."
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Cited by 62 (18 self)
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This chapter provides a modern overview of the field of hybrid logic. Hybrid logics are extensions of standard modal logics, involving symbols that name individual states in models. The first results that are nowadays considered as part of the field date back to the early work of Arthur
An Algebraic Approach to Data Languages and Timed Languages
, 2003
"... Algebra offers an elegant and powerful approach to understand regular languages and finite automata. Such framework has been notoriously lacking for timed languages and timed automata. We introduce the notion of monoid recognizability for data languages, which includes timed languages as special cas ..."
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Cited by 42 (1 self)
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Algebra offers an elegant and powerful approach to understand regular languages and finite automata. Such framework has been notoriously lacking for timed languages and timed automata. We introduce the notion of monoid recognizability for data languages, which includes timed languages as special case, in a way that respects the spirit of the classical situation. We study closure properties and hierarchies in this model, and prove that emptiness is decidable under natural hypotheses. Our class of recognizable languages properly includes many families of deterministic timed languages that have been proposed until now, and the same holds for nondeterministic versions.
The XML typechecking problem
 SIGMOD Record
"... When an XML document conforms to a given type (e.g. a DTD or an XML Schema type) it is called a valid document. Checking if a given XML document is valid is called the validation problem, and is typically performed by a parser (hence, validating parser), more precisely it is performed right after pa ..."
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Cited by 33 (0 self)
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When an XML document conforms to a given type (e.g. a DTD or an XML Schema type) it is called a valid document. Checking if a given XML document is valid is called the validation problem, and is typically performed by a parser (hence, validating parser), more precisely it is performed right after parsing, by the same program module. In practice however XML documents are often generated dynamically, by some
Model checking propositional dynamic logic with all extras
 Journal of Applied Logic
, 2005
"... This paper presents a model checking algorithm for Propositional Dynamic Logic (PDL) with looping, repeat, test, intersection, converse, program complementation as well as contextfree programs. The algorithm shows that the model checking problem for PDL remains PTIMEcomplete in the presence of all ..."
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Cited by 32 (6 self)
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This paper presents a model checking algorithm for Propositional Dynamic Logic (PDL) with looping, repeat, test, intersection, converse, program complementation as well as contextfree programs. The algorithm shows that the model checking problem for PDL remains PTIMEcomplete in the presence of all these operators, in contrast to the high increase in complexity that they cause for the satisfiability problem.