ACM Transactions on Database Systems

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A linear-time probabilistic counting algorithm for database applications
ACM Transactions on Database Systems - Tập 15 Số 2 - Trang 208-229 - 1990
Kyu-Young Whang, Brad T. Vander-Zanden, Howard M. Taylor
We present a probabilistic algorithm for counting the number of unique values in the presence of duplicates. This algorithm has O ( q ) time complexity, where q is the number of values including duplicates, and produces an estimation with an arbitrary accuracy prespecified by the user using only a small amount of space. Traditionally, accurate counts of unique values were obtained by sorting, whic... hiện toàn bộ
Efficient Sorting, Duplicate Removal, Grouping, and Aggregation
ACM Transactions on Database Systems - Tập 47 Số 4 - Trang 1-35 - 2022
Thanh Do, Goetz Graefe, Jeffrey F. Naughton
Database query processing requires algorithms for duplicate removal, grouping, and aggregation. Three algorithms exist: in-stream aggregation is most efficient by far but requires sorted input; sort-based aggregation relies on external merge sort; and hash aggregation relies on an in-memory hash table plus hash partitioning to temporary storage. Cost-based query optimization chooses which algorith... hiện toàn bộ
Join indices
ACM Transactions on Database Systems - Tập 12 Số 2 - Trang 218-246 - 1987
Patrick Valduriez
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 proper... hiện toàn bộ
Implications of certain assumptions in database performance evauation
ACM Transactions on Database Systems - Tập 9 Số 2 - Trang 163-186 - 1984
Stavros Christodoulakis
The assumptions of uniformity and independence of attribute values in a file, uniformity of queries, constant number of records per block, and random placement of qualifying records among the blocks of a file are frequently used in database performance evaluation studies. In this paper we show that these assumptions often result in predicting only an upper bound of the expected system cost. We the... hiện toàn bộ
Preference formulas in relational queries
ACM Transactions on Database Systems - Tập 28 Số 4 - Trang 427-466 - 2003
Jan Chomicki
The handling of user preferences is becoming an increasingly important issue in present-day information systems. Among others, preferences are used for information filtering and extraction to reduce the volume of data presented to the user. They are also used to keep track of user profiles and formulate policies to improve and automate decision making.We propose here a simple, logical framework fo... hiện toàn bộ
Optimizing object queries using an effective calculus
ACM Transactions on Database Systems - Tập 25 Số 4 - Trang 457-516 - 2000
Leonidas Fegaras, David Maier
Object-oriented databases (OODBs) provide powerful data abstractions and modeling facilities, but they generally lack a suitable framework for query processing and optimization. The development of an effective query optimizer is one of the key factors for OODB systems to successfully compete with relational systems, as well as to meet the performance requirements of many nontraditional application... hiện toàn bộ
A foundation for representing and querying moving objects
ACM Transactions on Database Systems - Tập 25 Số 1 - Trang 1-42 - 2000
Ralf Hartmut Güting, Michael H. Böhlen, Martin Erwig, Christian S. Jensen, Nikos A. Lorentzos, Markus Schneider, Michalis Vazirgiannis
Spatio-temporal databases deal with geometries changing over time. The goal of our work is to provide a DBMS data model and query language capable of handling such time-dependent geometries, including those changing continuously that describe moving objects . Two fundamental abstractions are moving point and moving region , describing objects for which only the time-dependent position, or position... hiện toàn bộ
A homogeneous relational model and query languages for temporal databases
ACM Transactions on Database Systems - Tập 13 Số 4 - Trang 418-448 - 1988
Shashi K. Gadia
In a temporal database, time values are associated with data item to indicate their periods of validity. We propose a model for temporal databases within the framework of the classical database theory. Our model is realized as a temporal parameterization of static relations. We do not impose any restrictions upon the schemes of temporal relations. The classical concepts of normal forms and depende... hiện toàn bộ
Towards a semantic view of an extended entity-relationship model
ACM Transactions on Database Systems - Tập 16 Số 3 - Trang 369-416 - 1991
Martin Gogolla, Uwe Hohenstein
Nearly all query languages discussed recently for the Entity-Relationship (ER) model do not possess a formal semantics. Languages are often defined by means of examples only. The reason for this phenomenon is the essential gap between features of query languages and theoretical foundations like algebras and calculi. Known languages offer arithmetic capabilities and allow for aggregates, but algebr... hiện toàn bộ
Join and Semijoin Algorithms for a Multiprocessor Database Machine
ACM Transactions on Database Systems - Tập 9 Số 1 - Trang 133-161 - 1984
Patrick Valduriez, Georges Gardarin
This paper presents and analyzes algorithms for computing joins and semijoins of relations in a multiprocessor database machine. First, a model of the multiprocessor architecture is described, incorporating parameters defining I/O, CPU, and message transmission times that permit calculation of the execution times of these algorithms. Then, three join algorithms are presented and compared. It is sh... hiện toàn bộ
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