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17
Inference of Message Sequence Charts
 Software Concepts and Tools
, 2003
"... Software designers draw Message Sequence Charts for early modeling of the individual behaviors they expect from the concurrent system under design. Can they be sure that precisely the behaviors they have described are realizable by some implementation of the components of the concurrent system? I ..."
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Cited by 186 (11 self)
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Software designers draw Message Sequence Charts for early modeling of the individual behaviors they expect from the concurrent system under design. Can they be sure that precisely the behaviors they have described are realizable by some implementation of the components of the concurrent system? If so, can we automatically synthesize concurrent state machines realizing the given MSCs? If, on the other hand, other unspecified and possibly unwanted scenarios are # A preliminary version of this paper appears in Proceedings of 22nd International Conference on Software Engineering, pages 304313, 2000. A journal version will appear in IEEE Transactions in Software Engineering, but due to space limitations in the journal, this is the fuller version.
On the Representation and Querying of Sets of Possible Worlds
, 1989
"... We represent a set of possible worlds using an incomplete information database. The representation techniques that we study range from the very simple Coddtable (a relation over constants and uniquely occurring variables called nulls) to much more complex mechanisms involving views of conditione ..."
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Cited by 115 (3 self)
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We represent a set of possible worlds using an incomplete information database. The representation techniques that we study range from the very simple Coddtable (a relation over constants and uniquely occurring variables called nulls) to much more complex mechanisms involving views of conditionedtables (programs applied to Coddtables augmented by equality and inequality conditions). (1) We provide matching upper and lower bounds on the datacomplexity of testing containment, membership, and uniqueness for sets of possible worlds. We fully classify these problems with respect to our representations. (2) We investigate the datacomplexity of querying incomplete information databases for both possible and certain facts. For each fixed positive existential query on conditionedtables we present a polynomial time algorithm solving the possible fact problem. We match this upper bound by two NPcompleteness lower bounds, when the fixed query contains either negation or recursion ...
A simplified universal relation assumption and its properties
 ACM Transactions on Database Systems
, 1982
"... One problem concerning the universal relation assumption is the inability of known methods to obtain a database scheme design in the general case, where the realworld constraints are given by a set of dependencies that includes embedded multivalued dependencies. We propose a simpler method of descr ..."
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Cited by 57 (0 self)
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One problem concerning the universal relation assumption is the inability of known methods to obtain a database scheme design in the general case, where the realworld constraints are given by a set of dependencies that includes embedded multivalued dependencies. We propose a simpler method of describing the real world, where constraints are given by functional dependencies and a single join dependency. The relationship between this method of defining the real world and the classical methods is exposed. We characterize in terms of hypergrapbs those multivalued dependencies that are the consequence of a given join dependency. Also characterized in terms of hypergraphs are those join dependencies that are equivalent to a set of multivalued dependencies.
Representing and querying XML with incomplete information
 ACM TODS
, 2006
"... We study the representation and querying of XML with incomplete information. We consider a simple model for XML data and their DTDs, a very simple query language, and a representation system for incomplete information in the spirit of the representations systems developed by Imielinski and Lipski [1 ..."
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Cited by 57 (7 self)
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We study the representation and querying of XML with incomplete information. We consider a simple model for XML data and their DTDs, a very simple query language, and a representation system for incomplete information in the spirit of the representations systems developed by Imielinski and Lipski [1984] for relational databases. In the scenario we consider, the incomplete information about an XML document is continuously enriched by successive queries to the document. We show that our representation system can represent partial information about the source document acquired by successive queries, and that it can be used to intelligently answer new queries. We also consider the impact on complexity of enriching our representation system or query language with additional features. The results suggest that our approach achieves a practically appealing balance between expressiveness and tractability.
J.B.: The chase revisited
 In: PODS (2008
"... We revisit the classical chase procedure, studying its properties as well as its applicability to standard database problems. We settle (in the negative) the open problem of decidability of termination of the standard chase, and we provide sufficient termination conditions which are strictly less ov ..."
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Cited by 54 (6 self)
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We revisit the classical chase procedure, studying its properties as well as its applicability to standard database problems. We settle (in the negative) the open problem of decidability of termination of the standard chase, and we provide sufficient termination conditions which are strictly less overconservative than the best previously known. We investigate the adequacy of the standard chase for checking query containment under constraints, constraint implication and computing certain answers in data exchange. We find room for improvement after gaining a deeper understanding of the chase by separating the algorithm from its result. We identify the properties of the chase result that are essential to the above applications, and we introduce the more general notion of an Funiversal model set, which supports query and constraint languages that are closed under a class F of mappings. By choosing F appropriately, we extend prior results all the way to existential firstorder queries and ∀∃firstorder constraints (and various standard sublanguages). We show that the standard chase is incomplete for finding universal model sets, and we introduce the extended core chase which is complete, i.e. finds an Funiversal model set when it exists. A key advantage of the new chase is that the same algorithm can be applied for the mapping classes F of interest, by simply modifying appropriately the set of constraints given as input. Even when restricted to the typical input in prior work (unions of conjunctive queries and embedded dependencies), the new chase supports certain answer computation and containment/implication tests in strictly more cases than the incomplete standard chase.
Flexible Queries over Semistructured Data
 IN PODS
, 2001
"... Flexible queries facilitate, in a novel way, easy and concise querying of databases that have varying structures. Two dierent semantics, exible and semiexible, are introduced and investigated. The complexity of evaluating queries under the two semantics is analyzed. Query evaluation is polynomial in ..."
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Cited by 42 (4 self)
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Flexible queries facilitate, in a novel way, easy and concise querying of databases that have varying structures. Two dierent semantics, exible and semiexible, are introduced and investigated. The complexity of evaluating queries under the two semantics is analyzed. Query evaluation is polynomial in the size of the query, the database and the result in the following two cases. First, a semiexible DAG query and a tree database. Second, a exible tree query and a database that is any graph. Query containment and equivalence are also investigated. For the exible semantics, query equivalence is always polynomial. For the semiexible semantics, query equivalence is polynomial for DAG queries and exponential when the queries have cycles. Under the semiexible and exible semantics, two databases could be equivalent even when they are not isomorphic. Database equivalence is formally de ned and characterized. The complexity of deciding equivalences among databases is analyzed. The implications of database equivalence on query evaluation are explained.
Characterization of desirable properties of general database decompositions
 Ann. Math. Art. Intell
, 1993
"... This paper appears in a special issue on database theory of the Annals of Mathematics ..."
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Cited by 10 (6 self)
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This paper appears in a special issue on database theory of the Annals of Mathematics
A Corrected 5NF Definition for Relational Database Design
, 1997
"... In this paper, the adequacy of fifth normal form (5NF) in relational database design is investigated. It is shown that 5NF is inadequate because it does not generalise fourth normal form (4NF) and because it is equivalent to the very stringent requirement that every attribute is a key, a requirement ..."
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Cited by 9 (4 self)
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In this paper, the adequacy of fifth normal form (5NF) in relational database design is investigated. It is shown that 5NF is inadequate because it does not generalise fourth normal form (4NF) and because it is equivalent to the very stringent requirement that every attribute is a key, a requirement that is effectively impossible to satisfy in practical database design. By restricting the join dependencies (JDs) in the set of constraints to those that do not have superfluous components, the definition of 5NF is then changed to a new normal form, called reduced fifth normal form (5NFR), and it is shown that 5NFR generalises 4NF. It is also shown that 5NFR is a strictly weaker condition than projectionjoin normal form (PJ/NF), the other normal form that has been proposed for JDs.
An Incremental Algorithm for Computing Ranked Full Disjunctions
 In PODS
, 2005
"... The full disjunction is a variation of the join operator that maximally combines tuples from connected relations, while preserving all information in the relations. The full disjunction can be seen as a natural extension of the binary outerjoin operator to an arbitrary number of relations and is a u ..."
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Cited by 6 (3 self)
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The full disjunction is a variation of the join operator that maximally combines tuples from connected relations, while preserving all information in the relations. The full disjunction can be seen as a natural extension of the binary outerjoin operator to an arbitrary number of relations and is a useful operator for information integration. This paper presents the algorithm IncrementalFD for computing the full disjunction of a set of relations. IncrementalFD improves upon previous algorithms for computing the full disjunction in three ways. First, it has a lower total runtime when computing the full result and a lower runtime when computing only k tuples of the result, for any constant k. Second, for a natural class of ranking functions, IncrementalFD returns tuples in ranking order. Third, IncrementalFD can be adapted to have a blockbased execution, instead of a tuplebased execution. 1.
Redundancy Elimination and a New Normal Form for Relational Database Design
 Semantics in Databases
, 1998
"... . The relationship between redundancy elimination and normal forms in relational database design is investigated for the case where the constraints contain functional dependencies (FDs) and arbitrary join dependencies (JDs). Extending previous work on the relationship between fourth normal form (4NF ..."
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Cited by 6 (2 self)
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. The relationship between redundancy elimination and normal forms in relational database design is investigated for the case where the constraints contain functional dependencies (FDs) and arbitrary join dependencies (JDs). Extending previous work on the relationship between fourth normal form (4NF) and redundancy elimination, a general definition of redundancy is proposed which is applicable to any type of relational dependency including arbitrary JDs. It is then shown that redundancy is eliminated if and only if the set of dependencies satisfies a new condition called keycomplete normal form (KCNF). KCNF requires that the lefthand side of every FD is a superkey and that for every JD, every attribute in the relation scheme is contained in the union of the components of the JD which are superkeys. It is also shown that KCNF is a strictly weaker condition than projectionjoin normal form (PJ/NF), the original normal form proposed for JDs. 1 Introduction Although normalisation [11, 1...