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22
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.
Database Description with SDM: A Semantic Database Model
 ACM Transactions on Database Systems
, 1981
"... SDM is a highlevel semanticsbased database description and structuring formalism (database model) for databases. This database model is designed to capture more of the meaning of an application environment than is possible with contemporary database models. An SDM specification describes a databas ..."
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Cited by 178 (3 self)
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SDM is a highlevel semanticsbased database description and structuring formalism (database model) for databases. This database model is designed to capture more of the meaning of an application environment than is possible with contemporary database models. An SDM specification describes a database in terms of the kinds of entities that exist in the application environment, the classifications and groupings of those entities, and the structural interconnections among them. SDM provides a collection of highlevel modeling primitives to capture the semantics of an application environment. By accommodating derived information in a database structural specification, SDM allows the same information to be viewed in several ways; this makes it possible to directly accommodate the variety of needs and processing requirements typically present in database applications. The design of the present SDM is based on our experience in using a preliminary version of it. SDM is designed to enhance the effectiveness and usability of database systems. An SDM database description can serve as a formal specification and documentation tool for a database; it can provide a basis for supporting a variety of powerful user interface facilities, it can serve as a conceptual database model in the database design process; and, it can be used as the database model for a new kind of database management system.
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.
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 73 (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.
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.
Achievements of relational database schema design theory revisited
 Semantics in Databases, volume LCNS 1358
, 1998
"... Database schema design is seen as to decide on formats for timevarying instances, on rules for supporting inferences and on semantic constraints. Schema design aims at both faithful formalization of the application and optimization at design time. It is guided by four heuristics: Separation of Asp ..."
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Cited by 26 (2 self)
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Database schema design is seen as to decide on formats for timevarying instances, on rules for supporting inferences and on semantic constraints. Schema design aims at both faithful formalization of the application and optimization at design time. It is guided by four heuristics: Separation of Aspects, Separation of Specializations, Inferential Completeness and Unique Flavor. A theory of schema design is to investigate these heuristics and to provide insight into how syntactic properties of schemas are related to worthwhile semantic properties, how desirable syntactic properties can be decided or achieved algorithmically, and how the syntactic properties determine costs of storage, queries and updates. Some wellknown achievements of design theory for relational databases are reviewed: normal forms, view support, deciding implications of semantic constraints, acyclicity, design algorithms removing forbidden substructures.
The implication and finite implication problems for typed template dependencies
 Journal of Computer and System Sciences
, 1984
"... The class of typed template dependencies is a class of data dependencies that includes embedded multivalued and join dependencies. It is shown that the implication and the_/Inite implication problems for this class are unsolvable. An immediate corollary is that this class has no formal system for fi ..."
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Cited by 11 (0 self)
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The class of typed template dependencies is a class of data dependencies that includes embedded multivalued and join dependencies. It is shown that the implication and the_/Inite implication problems for this class are unsolvable. An immediate corollary is that this class has no formal system for finite implication. It is also shown how to construct a finite set of typed template dependencies whose implication and finite implication problems are unsolvable. The class of projected join dependencies is a proper subclass of the above class, and it generalizes slightly embedded join dependencies. It is shown that the implication and the finite implication problems for this class are also unsolvable. An immediate corollary is that this class has no universebounded formal system for either implication or finite implication. 1. INTR~OUCTI~N In the relational model one views the database as a collection of relations, where each relation is a set of tuples over some domain of values [ 141. One notable feature of this model is its being almost devoid of semantics. A tuple in a relation represents a relationship between certain values, but from the mere syntactic definition of the
A Formal Approach to the Definition and the Design of Conceptual Schemata for Database Systems
 ACM TODS
, 1982
"... This paper presents a rigorous approach to the definition and the design of graphical schemata in the framework of the relational data model. This approach uses and applies various concepts and analytical tools which were presented in a companion paper [33] ..."
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Cited by 7 (1 self)
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This paper presents a rigorous approach to the definition and the design of graphical schemata in the framework of the relational data model. This approach uses and applies various concepts and analytical tools which were presented in a companion paper [33]
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 5 (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...
On a problem of Fagin concerning multivalued dependencies in relational databases’, accepted for Theoretical Computer Science (TCS
 Theor. Comput. Sci
, 2006
"... Multivalued dependencies (MVDs) are an important class of relational constraints that is fundamental to relational database design. MVDs have been wellstudied in the literature, and several papers have investigated various sets of inference rules for the implication of MVDs. The problem of finding ..."
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Cited by 5 (5 self)
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Multivalued dependencies (MVDs) are an important class of relational constraints that is fundamental to relational database design. MVDs have been wellstudied in the literature, and several papers have investigated various sets of inference rules for the implication of MVDs. The problem of finding a minimal set of such inference rules is particularly interesting as this characterises the semantic interaction of MVDs in a syntactically convenient and nonredundant form. Reflexivity axiom, complementation rule, and pseudodifference rule form such a minimal set. The complementation rule plays a distinctive role as it takes into account the underlying relation schema R which the MVDs are defined on. The Raxiom ∅ R is much weaker than the complementation rule, but is sufficient to form a minimal set of inference rules together with augmentation and pseudodifference rule. Fagin has asked whether it is possible to reduce the power of the complementation rule and drop the augmentation rule at the same time and still obtain a complete set. It was argued that there is a tradeoff between complementation rule and augmentation rule, and