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338
Join Indices
- ACM Transactions on Database Systems
, 1987
"... In new application areas of relational database systems, such as artificial intelligence, the join operator is used more extensively than in conventional applications. In this paper, we propose a simple data structure, called a join index, for improving the performance of joins in the context of com ..."
Abstract
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Cited by 231 (4 self)
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In new application areas of relational database systems, such as artificial intelligence, the join operator is used more extensively than in conventional applications. In this paper, we propose a simple data structure, called a join index, for improving the performance of joins in the context of complex queries. For most of the joins, updates to join indices incur very little overhead. Some properties of a join index are (i) its efficient use of memory and adaptiveness to parallel execution, data type join predicates, (iv) its support for multirelation clustering, and (v) its use in representing directed graphs and in evaluating recursive queries. Finally, the analysis of the join algorithm using join indices shows its excellent performance.
Database Description with SDM: A Semantic Database Model
- ACM Transactions on Database Systems
, 1981
"... SDM is a high-level semantics-based 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 ..."
Abstract
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Cited by 216 (4 self)
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SDM is a high-level semantics-based 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 high-level 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.
Semantic data models
- ACM Computing Surveys
, 1988
"... Semantic data models have emerged from a requirement for more expressive conceptual data models. Current generation data models lack direct support for relationships, data abstraction, inheritance, constraints, unstructured objects, and the dynamic properties of an application. Although the need for ..."
Abstract
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Cited by 178 (4 self)
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Semantic data models have emerged from a requirement for more expressive conceptual data models. Current generation data models lack direct support for relationships, data abstraction, inheritance, constraints, unstructured objects, and the dynamic properties of an application. Although the need for data models with richer semantics is widely recognized, no single approach has won general acceptance. This paper describes the generic properties of semantic data models and presents a representative selection of models that have been proposed since the mid-1970s. In addition to explaining the features of the individual models, guidelines are offered for the comparison of models. The paper concludes with a discussion of future directions in the area of conceptual data modeling.
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 Codd-table (a relation over constants and uniquely occurring variables called nulls) to much more complex mechanisms involving views of conditione ..."
Abstract
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Cited by 145 (4 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 Codd-table (a relation over constants and uniquely occurring variables called nulls) to much more complex mechanisms involving views of conditioned-tables (programs applied to Coddtables augmented by equality and inequality conditions). (1) We provide matching upper and lower bounds on the data-complexity 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 data-complexity of querying incomplete information databases for both possible and certain facts. For each fixed positive existential query on conditioned-tables we present a polynomial time algorithm solving the possible fact problem. We match this upper bound by two NP-completeness lower bounds, when the fixed query contains either negation or recursion ...
A survey of schema versioning issues for database systems
- Information and Software Technology
, 1995
"... Schema versioning is one of a number of related areas dealing with the same general problem- that of using multiple heterogeneous schemata for various database related tasks. In particular, schema versioning, and its weaker companion, schema evolution, deal with the need to retain current data and s ..."
Abstract
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Cited by 143 (5 self)
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Schema versioning is one of a number of related areas dealing with the same general problem- that of using multiple heterogeneous schemata for various database related tasks. In particular, schema versioning, and its weaker companion, schema evolution, deal with the need to retain current data and software system functionality in the face of changing database structure. Schema versioning and schema evolution offer a solution to the problem by enabling intelligent handling of any temporal mismatch between data and data structure. This survey discusses the modelling, architectural and query language issues relating to the support of evolving schemata in database systems. An indication of the future directions of schema versioning research are also given.
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 103 (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 graph-theoretic 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.
A Shared, Segmented Memory System for an Object-Oriented Database
- ACM Trans. on Office Information Systems
, 1987
"... This paper describes the basic data model of an object-oriented database and the basic architecture of the system implementing it. In particular, a secondary storage segmentation scheme and a transaction-processing scheme are discussed. The segmentation scheme allows for arbitrary clustering of obje ..."
Abstract
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Cited by 99 (2 self)
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This paper describes the basic data model of an object-oriented database and the basic architecture of the system implementing it. In particular, a secondary storage segmentation scheme and a transaction-processing scheme are discussed. The segmentation scheme allows for arbitrary clustering of objects, including duplicates. The transaction scheme allows for many different sharing protocols ranging from those that enforce serializability to those that are nonserializable and require communication with the server only on demand. The interaction of these two features is described such that segment-level transfer and object-level locking is achieved.
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 96 (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.
Current Approaches to Handling Imperfect Information in Data and Knowledge Bases
, 1996
"... This paper surveys methods for representing and reasoning with imperfect information. It opens with an attempt to classify the different types of imperfection that may pervade data, and a discussion of the sources of such imperfections. The classification is then used as a framework for considering ..."
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Cited by 70 (1 self)
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This paper surveys methods for representing and reasoning with imperfect information. It opens with an attempt to classify the different types of imperfection that may pervade data, and a discussion of the sources of such imperfections. The classification is then used as a framework for considering work that explicitly concerns the representation of imperfect information, and related work on how imperfect information may be used as a basis for reasoning. The work that is surveyed is drawn from both the field of databases and the field of artificial intelligence. Both of these areas have long been concerned with the problems caused by imperfect information, and this paper stresses the relationships between the approaches developed in each.
Conceptual Modelling and Telos
"... We review basic premises underlying the application of conceptual modelling to the development of information systems and point out a fundamental problem arising from the broad range of concepts that need to be modelled. We then argue that conventional conceptual models are weak for such broad domai ..."
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Cited by 69 (2 self)
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We review basic premises underlying the application of conceptual modelling to the development of information systems and point out a fundamental problem arising from the broad range of concepts that need to be modelled. We then argue that conventional conceptual models are weak for such broad domains of discourse because they come with built-in collections of primitive notions in terms of which conceptual modelling is to be done. Telos is then introduced as a conceptual modelling language designed for capturing knowledge about information systems and it is argued that, unlike its peers, it offers facilities not only for modelling an application but also the notions used to model an application. The presentation of features of the language is eclectic and generally non-technical. Details about Telos can be found in [Mylopoulos90] and [Koubarakis89].
