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25
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 245 (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.
A Logical Design Methodology for Relational Databases Using the Extended EntityRelationship Model
 ACM Computing Surveys
, 1986
"... A database design methodology is defined for the design of large relational databases. First, the data requirements are conceptualized using an extended entityrelationship model, with the extensions being additional semantics such as ternary relationships, optional relationships, and the generaliza ..."
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Cited by 141 (1 self)
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A database design methodology is defined for the design of large relational databases. First, the data requirements are conceptualized using an extended entityrelationship model, with the extensions being additional semantics such as ternary relationships, optional relationships, and the generalization abstraction. The extended entityrelationship model is then decomposed according to a set of basic entityrelationship constructs, and these are transformed into candidate relations. A set of basic transformations has been developed for the three types of relations: entity relations, extended entity relations, and relationship relations. Candidate relations are further analyzed and modified to attain the highest degree of normalization desired. The methodology produces database designs that are not only accurate representations of reality, but flexible enough to accommodate future processing requirements. It also reduces the number of data dependencies that must be analyzed, using the extended ER model conceptualization, and maintains data integrity through normalization. This approach can be implemented manually or in a simple software package as long as a “good ” solution is acceptable and absolute optimality is not required.
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 113 (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.
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.
A New Normal Form for Nested Relations
 ACM Transactions on Database Systems
, 1987
"... We consider nested relations whose schemes are structured as trees, called scheme trees, and introduce a normal form for such relations, called the nested normal form. Given a set of attributes U, and a set of multivalued dependencies (MVDs) M over these attributes, we present an algorithm to obtain ..."
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Cited by 51 (2 self)
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We consider nested relations whose schemes are structured as trees, called scheme trees, and introduce a normal form for such relations, called the nested normal form. Given a set of attributes U, and a set of multivalued dependencies (MVDs) M over these attributes, we present an algorithm to obtain a nested normal form decomposition of U with respect to M. Such a decomposition has several desirable properties, such as explicitly representing a set of full and embedded MVDs implied by M, and being a faithful and nonredundant representation of U. Moreover, if the given set of MVDs is conflict free, then the nested normal form decomposition is also dependency preserving. Finally, we show that if M is conflict free, then the set of roottoleaf paths of scheme trees in nested normal form decomposition is precisely the unique 4NF decomposition [Fa, L2] of U with respect to M. 1. Introduction A relational database [Co] is a collection of relations where each relation is at least in First ...
An InformationTheoretic Approach to Normal Forms for Relational and XML Data
 In PODS
, 2003
"... Normalization as a way of producing good database designs is a wellunderstood topic. ..."
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Cited by 45 (8 self)
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Normalization as a way of producing good database designs is a wellunderstood topic.
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 27 (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.
Unique complements and decompositions of database schemata
 Journal of Computer and System Sciences
, 1994
"... In earlier work, Bancilhon and Spyratos introduced the concept of a complement to a database schema, and showed how this notion could be used in theories of decomposition and update semantics. However, they also showed that, except in trivial cases, even minimal complements are never unique, so that ..."
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Cited by 14 (8 self)
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In earlier work, Bancilhon and Spyratos introduced the concept of a complement to a database schema, and showed how this notion could be used in theories of decomposition and update semantics. However, they also showed that, except in trivial cases, even minimal complements are never unique, so that many desirable results, such as canonical decompositions, cannot be realized. Their work dealt with database schemata which are sets and database mappings which are functions, without further structure. In this work, we show that by adding a modest amount of additional structure, many important uniqueness results may be obtained. Specifically, we work with database schemata whose legal states form partially ordered sets (posets) with least elements, and with database mappings which are isotonic and which preserve this least element. This is a natural algebraic structure which is inherent in many important examples, including relational schemata constrained by data dependencies, with views constructed by composition of projection, restriction, and selection. Other examples include deductive database schemata in which views are defined by rules, and general firstorder logic databases.
On redundancy vs dependency preservation in normalization: an informationtheoretic study of 3NF
 In Proceedings of the 25th ACM SIGACTSIGMODSIGART Symposium on Principles of Database Systems
"... A recently introduced informationtheoretic approach to analyzing redundancies in database design was used to justify normal forms like BCNF that completely eliminate redundancies. The main notion is that of an information content of each datum in an instance (which is a number in [0, 1]): the close ..."
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Cited by 9 (5 self)
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A recently introduced informationtheoretic approach to analyzing redundancies in database design was used to justify normal forms like BCNF that completely eliminate redundancies. The main notion is that of an information content of each datum in an instance (which is a number in [0, 1]): the closer to 1, the less redundancy it carries. In practice, however, one usually settles for 3NF which, unlike BCNF, may not eliminate all redundancies but always guarantees dependency preservation. In this paper we use the informationtheoretic approach to prove that 3NF is the best normal form if one needs to achieve dependency preservation. For each dependencypreserving normal form, we define the price of dependency preservation as an informationtheoretic measure of redundancy that gets introduced to compensate for dependency preservation. This is a number in the [0, 1] range: the smaller it is, the less redundancy a normal form guarantees. We prove that for every dependencypreserving normal form, the price of dependency preservation is at least 1/2, and it is precisely 1/2 for 3NF. Hence, 3NF has the least amount of redundancy among all dependencypreserving normal forms. We also show that, informationtheoretically, unnormalized schemas have at least twice the amount of redundancy than schemas in 3NF. 1.
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]