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70
Extending the Database Relational Model to Capture More Meaning
 ACM Transactions on Database Systems
, 1979
"... During the last three or four years several investigators have been exploring “semantic models ” for formatted databases. The intent is to capture (in a more or less formal way) more of the meaning of the data so that database design can become more systematic and the database system itself can beha ..."
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Cited by 250 (1 self)
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During the last three or four years several investigators have been exploring “semantic models ” for formatted databases. The intent is to capture (in a more or less formal way) more of the meaning of the data so that database design can become more systematic and the database system itself can behave more intelligently. Two major thrusts are clear: (I) the search for meaningful units that are as small as possibleatomic semantics; (2) the search for meaningful units that are larger than the usual nary relationmolecular semantics. In this paper we propose extensions to the relational model to support certain atomic and molecular semantics. These extensions represent a synthesis of many ideas from the published work in semantic modeling plus the introduction of new rules for insertion, update, and deletion, as well as new algebraic operators.
Query optimization in database systems
 ACM Computing Surveys
, 1984
"... Efficient methods of processing unanticipated queries are a crucial prerequisite for the success of generalized database management systems. A wide variety of approaches to improve the performance of query evaluation algorithms have been proposed: logicbased and semantic transformations, fast imple ..."
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Cited by 207 (0 self)
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Efficient methods of processing unanticipated queries are a crucial prerequisite for the success of generalized database management systems. A wide variety of approaches to improve the performance of query evaluation algorithms have been proposed: logicbased and semantic transformations, fast implementations of basic operations, and combinatorial or heuristic algorithms for generating alternative access plans and choosing among them. These methods are presented in the framework of a general query evaluation procedure using the relational calculus representation of queries. In addition, nonstandard query optimization issues such as higher level query evaluation, query optimization in distributed databases, and use of database machines are addressed. The focus, however, is on query optimization in centralized database systems.
Testing implications of data dependencies
 ACM Transactions on Database Systems
, 1979
"... Presented is a computation methodthe chasefor testing implication of data dependencies by a set of data dependencies. The chase operates on tableaux similar to those of Aho, Sagiv, and Ullman. The chase includes previous tableau computation methods as special cases. By interpreting tableaux altern ..."
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Cited by 114 (3 self)
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Presented is a computation methodthe chasefor testing implication of data dependencies by a set of data dependencies. The chase operates on tableaux similar to those of Aho, Sagiv, and Ullman. The chase includes previous tableau computation methods as special cases. By interpreting tableaux alternately as mappings or as templates for relations, it is possible to test implication of join dependencies (including multivalued dependencies) and functional dependencies by a set of dependencies.
Monadic Datalog and the Expressive Power of Languages for Web Information Extraction
 J. ACM
, 2002
"... Research on information extraction from Web pages (wrapping) has seen much activity in recent times (particularly systems implementations), but little work has been done on formally studying the expressiveness of the formalisms proposed or on the theoretical foundations of wrapping. In this paper, w ..."
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Cited by 75 (11 self)
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Research on information extraction from Web pages (wrapping) has seen much activity in recent times (particularly systems implementations), but little work has been done on formally studying the expressiveness of the formalisms proposed or on the theoretical foundations of wrapping. In this paper, we first study monadic datalog as a wrapping language (over ranked or unranked tree structures). Using previous work by Neven and Schwentick, we show that this simple language is equivalent to full monadic second order logic (MSO) in its ability to specify wrappers. We believe that MSO has the right expressiveness required for Web information extraction and thus propose MSO as a yardstick for evaluating and comparing wrappers. Using the above result, we study the kernel fragment Elog of the Elog wrapping language used in the Lixto system (a visual wrapper generator). The striking fact here is that Elog exactly captures MSO, yet is easier to use. Indeed, programs in this language can be entirely visually specified. We also formally compare Elog to other wrapping languages proposed in the literature.
Fuzzy functional dependencies and lossless join decomposition of fuzzy relational database systems
 ACM Transactions on Database Systems
, 1988
"... This paper deals with the application of fuzzy logic in a relational database environment with the objective of capturing more meaning of the data. It is shown that with suitable interpretations for the fuzzy membership functions, a fuzzy relational data model can be used to represent ambiguities in ..."
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Cited by 75 (0 self)
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This paper deals with the application of fuzzy logic in a relational database environment with the objective of capturing more meaning of the data. It is shown that with suitable interpretations for the fuzzy membership functions, a fuzzy relational data model can be used to represent ambiguities in data values as well as impreciseness in the association among them. Relational operators for fuzzy relations have been studied, and applicability of fuzzy logic in capturing integrity constraints has been investigated. By introducing a fuzzy resemblance measure EQUAL for comparing domain values, the definition of classical functional dependency has been generalized to fuzzy functional dependency (ffd). The implication problem of ffds has been examined and a set of sound and complete inference axioms has been proposed. Next, the problem of lossless join decomposition of fuzzy relations for a given set of fuzzy functional dependencies is investigated. It is proved that with a suitable restriction on EQUAL, the design theory of a classical relational database with functional dependencies can be extended to fuzzy relations satisfying fuzzy functional dependencies.
Horn clauses and database dependencies
 Journal of the ACM
, 1982
"... Abstract. Certain firstorder sentences, called "dependencies, " about relations in a database are defined and studied. These dependencies seem to include all prewously defined dependencies as special cases A new concept is mtroduced, called "faithfulness (with respect to ..."
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Cited by 62 (6 self)
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Abstract. Certain firstorder sentences, called &quot;dependencies, &quot; about relations in a database are defined and studied. These dependencies seem to include all prewously defined dependencies as special cases A new concept is mtroduced, called &quot;faithfulness (with respect to direct product), &quot; which enables powerful results to be proved about the existence of &quot;Armstrong relations &quot; in the presence of these new dependencies. (An Armstrong relaUon is a relation that obeys precisely those dependencies that are the logical consequences of a given set of dependencies.) Results are also obtained about characterizing the class of projections of those relations that obey a given set of dependencies.
10^(10^6) Worlds and Beyond: Efficient Representation and Processing of Incomplete Information
, 2006
"... Current systems and formalisms for representing incomplete information generally suffer from at least one of two weaknesses. Either they are not strong enough for representing results of simple queries, or the handling and processing of the data, e.g. for query evaluation, is intractable. In this pa ..."
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Cited by 61 (8 self)
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Current systems and formalisms for representing incomplete information generally suffer from at least one of two weaknesses. Either they are not strong enough for representing results of simple queries, or the handling and processing of the data, e.g. for query evaluation, is intractable. In this paper, we present a decompositionbased approach to addressing this problem. We introduce worldset decompositions (WSDs), a spaceefficient formalism for representing any finite set of possible worlds over relational databases. WSDs are therefore a strong representation system for any relational query language. We study the problem of efficiently evaluating relational algebra queries on sets of worlds represented by WSDs. We also evaluate our technique experimentally in a large census data scenario and show that it is both scalable and efficient.
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 58 (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.
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 56 (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.
An Equational Chase for PathConjunctive Queries, Constraints, and Views
 In ICDT
, 1999
"... We consider the class of pathconjunctive queries and constraints (dependencies) defined over complex values with dictionaries. ..."
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Cited by 44 (12 self)
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We consider the class of pathconjunctive queries and constraints (dependencies) defined over complex values with dictionaries.