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20
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 242 (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.
Logic and databases: a deductive approach
 ACM Computing Surveys
, 1984
"... The purpose of this paper is to show that logic provides a convenient formalism for studying classical database problems. There are two main parts to the paper, devoted respectively to conventional databases and deductive databases. In the first part, we focus on query languages, integrity modeling ..."
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Cited by 143 (2 self)
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The purpose of this paper is to show that logic provides a convenient formalism for studying classical database problems. There are two main parts to the paper, devoted respectively to conventional databases and deductive databases. In the first part, we focus on query languages, integrity modeling and maintenance, query optimization, and data
Multivalued Dependencies and a New Normal Form for Relational Databases
 ACM Transactions on Database Systems
, 1977
"... A new type of dependency, which includes the wellknown functional dependencies as a special case, is defined for relational databases. By using this concept, a new (“fourth”) normal form for relation schemata is defined. This fourth normal form is strictly stronger than Codd’s “improved third norm ..."
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Cited by 116 (5 self)
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A new type of dependency, which includes the wellknown functional dependencies as a special case, is defined for relational databases. By using this concept, a new (“fourth”) normal form for relation schemata is defined. This fourth normal form is strictly stronger than Codd’s “improved third normal form ” (or “BoyceCodd normal form”). It is shown that, every relation schema can be decomposed into a family of relation schemata in fourth normal form without loss of information (that is, the original relation can be obtained from the new relations by taking joins). Key words and phrases: database design, multivalued dependency, functional dependency, fourth normal form, 4NF, third normal form, 3NF, BoyceCodd normal form, normalization, decomposition, relational database
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 110 (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.
Degrees of acyclicity for hypergraphs and relational database schemes
 Journal of the ACM
, 1983
"... Abstract. Database schemes (winch, intuitively, are collecuons of table skeletons) can be wewed as hypergraphs (A hypergraph Is a generalization of an ordinary undirected graph, such that an edge need not contain exactly two nodes, but can instead contain an arbitrary nonzero number of nodes.) A cla ..."
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Cited by 73 (2 self)
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Abstract. Database schemes (winch, intuitively, are collecuons of table skeletons) can be wewed as hypergraphs (A hypergraph Is a generalization of an ordinary undirected graph, such that an edge need not contain exactly two nodes, but can instead contain an arbitrary nonzero number of nodes.) A class of "acychc " database schemes was recently introduced. A number of basic desirable propemes of database schemes have been shown to be equivalent to acyclicity This shows the naturalness of the concept. However, unlike the situation for ordinary, undirected graphs, there are several natural, noneqmvalent notions of acyclicity for hypergraphs (and hence for database schemes). Various desirable properties of database schemes are constdered and it is shown that they fall into several equivalence classes, each completely characterized by the degree of acycliclty of the scheme The results are also of interest from a purely graphtheoretic viewpomt. The original notion of aeyclicity has the countermtmtive property that a subhypergraph of an acychc hypergraph can be cyclic. This strange behavior does not occur for the new degrees of acyelicity that are considered.
Database Relations with Null Values
, 1984
"... this paper we briefly review some of these issues and then concentrate on the problem of generalizing the formal framework of the relational data model to include null values. A basic problem with null values is that they have many plausible interpretations. The ANSI/SPARC interim report, for instan ..."
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Cited by 60 (0 self)
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this paper we briefly review some of these issues and then concentrate on the problem of generalizing the formal framework of the relational data model to include null values. A basic problem with null values is that they have many plausible interpretations. The ANSI/SPARC interim report, for instance, cites 14 different manifestations of nulls. Most authors, however, agree that the various manifestations of nulls can be reduced to two basic interpretations. These are: (a) the unknown interpretation: a value exists but it is not known; and lb) the nonexistent interpretation: a value does not exist
On the structure of Armstrong relations for functional dependencies
 Journal of the ACM
, 1984
"... Abstract. An Armstrong relation for a set of functional dependencies (FDs) is a relation that satisfies each FD implied by the set but no FD that is not implied by it. The structure and size (number of tuples) of Armstrong relatsons are investigated. Upper and lower bounds on the size of minimalsiz ..."
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Cited by 42 (3 self)
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Abstract. An Armstrong relation for a set of functional dependencies (FDs) is a relation that satisfies each FD implied by the set but no FD that is not implied by it. The structure and size (number of tuples) of Armstrong relatsons are investigated. Upper and lower bounds on the size of minimalsized Armstrong relations are derived, and upper and lower bounds on the number of distinct entries that must appear m an Armstrong relation are given. It is shown that the time complexity of finding an Armstrong relation, gwen a set of functional dependencies, is precisely exponential in the number of attributes. Also shown,s the falsity of a natural conjecture which says that almost all relations obeying a given set of FDs are Armstrong relations for that set of FDs. Finally, Armstrong relations are used to generahze a result, obtained by Demetrovics using quite complicated methods, about the possible sets of keys for a relauon.
Semantics of TimeVarying Information
 INFORMATION SYSTEMS
, 1996
"... This paper provides a systematic and comprehensive study of the underlying semantics of temporal databases, summarizing the results of an intensive collaboration between the two authors over the last five years. We first examine how facts may be associated with time, most prominently with one or mor ..."
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Cited by 36 (19 self)
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This paper provides a systematic and comprehensive study of the underlying semantics of temporal databases, summarizing the results of an intensive collaboration between the two authors over the last five years. We first examine how facts may be associated with time, most prominently with one or more dimensions of valid time and transaction time. One common case is that of a bitemporal relation, in which facts are associated with exactly one valid time and one transaction time. These two times may be related in various ways, yielding temporal specialization. Multiple transaction times arise when a fact is stored in one database, then later replicated or transferred to another database. By retaining the transaction times, termed temporal generalization, the original relation can be effectively queried by referencing only the final relation. We attempt to capture the essence of timevarying information via a very simple data model, the bitemporal conceptual data model. Emphasis is placed...
Extending Existing Dependency Theory to Temporal Databases
 IEEE Trans. on Knowledge and Data Engineering
, 1994
"... Normal forms play a central role in the design of relational databases. Several normal forms for temporal relational databases have been proposed. These definitions are particular to specific temporal data models, which are numerous and incompatible. ..."
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Cited by 20 (8 self)
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Normal forms play a central role in the design of relational databases. Several normal forms for temporal relational databases have been proposed. These definitions are particular to specific temporal data models, which are numerous and incompatible.
On the complexity of join dependencies
 ACM Trans. Database Syst
, 1986
"... In [IO] a method is proposed for decomposing join dependencies (jds) in a relational database using the notion of a hinge. This method was subsequently studied in [ll] and [El. We show how the technique of decompasiti” ” can be used t ” make integrity checking m”re efficient. It turns ““t that it is ..."
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Cited by 15 (2 self)
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In [IO] a method is proposed for decomposing join dependencies (jds) in a relational database using the notion of a hinge. This method was subsequently studied in [ll] and [El. We show how the technique of decompasiti” ” can be used t ” make integrity checking m”re efficient. It turns ““t that it is important t ” find a decomposition that minimizes the “umber of edges of its largest element. We show that the decompositions obtained with the method described in (lo] are optimal in this respect. This minimality criterion leads ta the definition of the degree of cy&ity, which allows us t” classify jds and leads to the notion of ncyel*i@, of which acyclicity is a special case for n = 2. We then show that, for a fixed value of n (which may be greater than 2). integrity checking can be performed in polynomial time provided we restrict ourselves t ” ncyclic jds. Finally, we generalize a wellknown characterization for acyclic jds by proving that ncyclicity is equivalent ta “nwise consistency implies global consistency. ” As a consequence, consistency checking can be performed in polynomial time if we restrict aurselves to ncyclic jds, for a tired value of n, not necessarily equal t ” 2.