Results 1  10
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19
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 229 (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.
A Probabilistic Relational Algebra for the Integration of Information Retrieval and Database Systems
 ACM Transactions on Information Systems
, 1994
"... We present a probabilistic relational algebra (PRA) which is a generalization of standard relational algebra. Here tuples are assigned probabilistic weights giving the probability that a tuple belongs to a relation. Based on intensional semantics, the tuple weights of the result of a PRA expression ..."
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Cited by 211 (34 self)
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We present a probabilistic relational algebra (PRA) which is a generalization of standard relational algebra. Here tuples are assigned probabilistic weights giving the probability that a tuple belongs to a relation. Based on intensional semantics, the tuple weights of the result of a PRA expression always confirm to the underlying probabilistic model. We also show for which expressions extensional semantics yields the same results. Furthermore, we discuss complexity issues and indicate possibilities for optimization. With regard to databases, the approach allows for representing imprecise attribute values, whereas for information retrieval, probabilistic document indexing and probabilistic search term weighting can be modelled. As an important extension, we introduce the concept of vague predicates which yields a probabilistic weight instead of a Boolean value, thus allowing for queries with vague selection conditions. So PRA implements uncertainty and vagueness in combination with the...
Models for Integrated Information Retrieval and Database Systems
 IEEE Data Engineering Bulletin
, 1996
"... In this paper, we show that there is a mismatch between information retrieval (IR) and database (DB) concepts, and we devise solutions for this problem. DB oriented approaches have to distinguish between the logical and the content structure of objects, and should also consider the layout structure. ..."
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Cited by 17 (0 self)
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In this paper, we show that there is a mismatch between information retrieval (IR) and database (DB) concepts, and we devise solutions for this problem. DB oriented approaches have to distinguish between the logical and the content structure of objects, and should also consider the layout structure. Data independence — not regarded in IR before — can be achieved by using the notion of vague predicates. Since IR is based on uncertain inference, data models with uncertainty are required for an integrated IRDB system. For this purpose, we present a probabilistic relational algebra. As extensions, probabilistic Datalog yields a more expressive query language, whereas a probabilistic nested relational model is more appropriate for modelling document structures. 1
A Probabilistic NF2 Relational Algebra for Imprecision in
, 1996
"... We present a probabilistic data model which is based on relations in nonfirstnormalform (NF2). Here, tuples are assigned probabilistic weights giving the probability that a tuple belongs to a relation. This way, imprecise attribute values are modelled as a probabilistic subrelation. ..."
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Cited by 14 (2 self)
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We present a probabilistic data model which is based on relations in nonfirstnormalform (NF2). Here, tuples are assigned probabilistic weights giving the probability that a tuple belongs to a relation. This way, imprecise attribute values are modelled as a probabilistic subrelation.
A Probabilistic NF2 Relational Algebra for Integrated Information Retrieval and Database Systems
 In Proceedings of the 2nd World Conference on Integrated Design and Process Technology
, 1996
"... The integration of information retrieval (IR) and database systems requires a data model which allows for modelling documents as entities, representing uncertainty and vagueness and performing uncertain inference. For this purpose, we present a probabilistic data model based on relations in nonfirst ..."
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Cited by 9 (1 self)
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The integration of information retrieval (IR) and database systems requires a data model which allows for modelling documents as entities, representing uncertainty and vagueness and performing uncertain inference. For this purpose, we present a probabilistic data model based on relations in nonfirst normalform (NF2). Here, tuples are assigned probabilistic weights giving the probability that a tuple belongs to a relation. Thus, the set of weighted index terms of a document are represented as a probabilistic subrelation. In a similar way, imprecise attribute values are modelled as a setvalued attribute. We redefine the relational operators for this type of relations such that the result of each operator is again a probabilistic NF2 relation, where the weight of a tuple gives the probability that this tuple belongs to the result. By ordering the tuples according to decreasing probabilities, the model yields a ranking of answers like in most IR models. This effect also can be used for ...
Tool Construction for ProcessCentred Software Development Environments Based on Object Databases
, 1995
"... The aim of this thesis is to discuss the construction of tools for processcentred software development environments (PSDEs). Our main contribution is the proof that object database systems are a very suitable basis for improving the functionality of software development tools and for integrating th ..."
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Cited by 8 (6 self)
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The aim of this thesis is to discuss the construction of tools for processcentred software development environments (PSDEs). Our main contribution is the proof that object database systems are a very suitable basis for improving the functionality of software development tools and for integrating them in PSDEs. We set out to prove this hypothesis following engineering principles rather than in an analytic or empiric way. We, therefore, first discuss the functionality that software developers require from tools contained in a PSDE. Starting from these requirements, we take the position of a tool builder and delineate requirements for a database system for document management purposes. We then review how well existing database systems satisfy these requirements. This results in the selection of object database systems as the most promising systems to take. We then propose a tool architecture that is based on object databases. We classify the components of this architecture into component...
Future Database technology: Driving Forces . . .
 LECTURE AND NOTES IN COMPUTER SCIENCE NO. 466, DATABASE SYSTEMS OF THE 90S
, 1990
"... ..."
FEMUS: a FEderated MUltilingual database System
 of Lecture Notes in Computer Science, chapter 18.4
, 1993
"... This paper describes the objectives and goals of the FEMUS project, a joint research project of the database research groups at EPF Lausanne and ETH Zrich. It presents an overview on FEMUS and the first results on comparison between ERC+ and COCOON. ..."
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Cited by 3 (0 self)
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This paper describes the objectives and goals of the FEMUS project, a joint research project of the database research groups at EPF Lausanne and ETH Zrich. It presents an overview on FEMUS and the first results on comparison between ERC+ and COCOON.
Extensions to the Relational Data Model
 Conceptual Modelling, Databases and CASE: An Integrated View of Information Systems Development. Jon
, 1992
"... this paper we give an overview of research on extensions of relational database technology. In order to systematically classify different ways to extend the data model we take a programming language point of view of data models: a data model consists of a set of basic (predefined) types, a set of ty ..."
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Cited by 2 (1 self)
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this paper we give an overview of research on extensions of relational database technology. In order to systematically classify different ways to extend the data model we take a programming language point of view of data models: a data model consists of a set of basic (predefined) types, a set of type constructors (or structuring primitives), and a set of operators (for the predefined as well as constructed types). Extensions to each of of these data model constituents are possible and have indeed been investigated in the past. Our presentation focuses on extensions to the type system (primitives and constructors) and those extensions to the operators that are implied by them. During the 1980's, there has been a significant trend in database research addressing the problem of supporting nontraditional database applications. Though relational database systems (RDBMSs) entered the commercial marketplace in the early eighties, it seemed clear that, at least without major enhancements, they would not be appropriate for nonbusiness applications. Several research groups started out to either enhance RDBMS technology in several ways or to develop completely different models and systems. Throughout this paper we limit our scope to those investigations that tried to keep some of the characteristics of the relational model and/or systems. Attempts to make semantic data models operational, for instance, EntityRelationship models, have already been discussed in this volume before. Also, extensions in query languages' expressive power to deal with recursion, will be surveyed in a subsequent series of articles, as will the objectoriented approaches. Therefore, we will take a more "conservative" approach, that is, stay closer within the original relational framework. The relationa...