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Query evaluation techniques for large databases
 ACM COMPUTING SURVEYS
, 1993
"... Database management systems will continue to manage large data volumes. Thus, efficient algorithms for accessing and manipulating large sets and sequences will be required to provide acceptable performance. The advent of objectoriented and extensible database systems will not solve this problem. On ..."
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Cited by 644 (9 self)
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Database management systems will continue to manage large data volumes. Thus, efficient algorithms for accessing and manipulating large sets and sequences will be required to provide acceptable performance. The advent of objectoriented and extensible database systems will not solve this problem. On the contrary, modern data models exacerbate it: In order to manipulate large sets of complex objects as efficiently as today’s database systems manipulate simple records, query processing algorithms and software will become more complex, and a solid understanding of algorithm and architectural issues is essential for the designer of database management software. This survey provides a foundation for the design and implementation of query execution facilities in new database management systems. It describes a wide array of practical query evaluation techniques for both relational and postrelational database systems, including iterative execution of complex query evaluation plans, the duality of sort and hashbased set matching algorithms, types of parallel query execution and their implementation, and special operators for emerging database application domains.
Incremental Maintenance of Views with Duplicates
"... We study the problem of efficient maintenance of materialized views that may contain duplicates. This problem is particularly important when queries against such views involve aggregate functions, which need duplicates to produce correct results. Unlike most work on the view maintenance problem that ..."
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Cited by 164 (8 self)
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We study the problem of efficient maintenance of materialized views that may contain duplicates. This problem is particularly important when queries against such views involve aggregate functions, which need duplicates to produce correct results. Unlike most work on the view maintenance problem that is based on an algorithmic approach, our approach is algebraic and based on equational reasoning. This approach has a number of advantages: it is robust and easily extendible to new language constructs, it produces output that can be used by query optimizers, and it simpli es correctness proofs. We use a natural extension of the relational algebra operations to bags (multisets) as our basic language. We present an algorithm that propagates changes from base relations to materialized views. This algorithm is based on reasoning about equivalence of bagvalued expressions. We prove that it is correct and preserves a certain notion of minimality that ensures that no unnecessary tuples are computed. Although it is generally only a heuristic that computing changes to the view rather than recomputing the view from scratch is more efficient, we prove results saying that under normal circumstances one should expect the change propagation algorithm to be significantly faster and more space efficient than complete recomputing of the view. We also show that our approach interacts nicely with aggregate functions, allowing their correct evaluation on views that change.
On The Power Of Languages For The Manipulation Of Complex Objects
 In Proceedings of International Workshop on Theory and Applications of Nested Relations and Complex Objects
, 1993
"... Various models and languages for describing and manipulating hierarchically structured data have been proposed. Algebraic, calculusbased and logicprogramming oriented languages have all been considered. This paper presents a general model for complex objects, and languages for it based on the thre ..."
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Cited by 121 (6 self)
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Various models and languages for describing and manipulating hierarchically structured data have been proposed. Algebraic, calculusbased and logicprogramming oriented languages have all been considered. This paper presents a general model for complex objects, and languages for it based on the three paradigms. The algebraic language generalizes those presented in the literature; it is shown to be related to the functional style of programming advocated by Backus. The notion of domain independence familiar from relational databases is defined, and syntactic restrictions (referred to as safety conditions) on calculus queries are formulated, that guarantee domain independence. The main results are: The domainindependent calculus, the safe calculus, the algebra, and the logicprogramming oriented language have equivalent expressive power. In particular, recursive queries, such as the transitive closure, can be expressed in each of the languages. For this result, the algebra needs the pow...
Semantics of Logic Programs with Aggregates
 In Proceedings of the International Logic Programming Symposium
, 1991
"... We investigate the semantics of aggregates (count, sum, : : :) in logic programs with function symbols and negation. In particular we address the meaning of programs with recursion through aggregation. We extend the two most successful semantic approaches to the problem of recursion through negation ..."
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Cited by 66 (2 self)
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We investigate the semantics of aggregates (count, sum, : : :) in logic programs with function symbols and negation. In particular we address the meaning of programs with recursion through aggregation. We extend the two most successful semantic approaches to the problem of recursion through negation, well founded models and stable models, to programs with aggregates. We examine previously defined classes of aggregate programs: aggregate stratified, group stratified, magical stratified, monotonic and closed semiring programs and relate our semantics to those previously defined. The wellfounded model gives a semantics to all programs containing aggregates, and agrees with twovalued models already defined for aggregate and group stratified programs. Stable models give a meaning to many programs with aggregation, including all of the above classes, and captures all the models that have been previously defined. Further, there are programs not captured in any previously defined class wher...
The Magic of Duplicates and Aggregates
, 1990
"... We present a formal treatment of multisets (that arise when duplicates are not eliminated) and aggregate operators for deductive and relational databases. We define the semantics rigorously and extend the magicsets technique to programs containing multisets and aggregates. The work presented here i ..."
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Cited by 59 (5 self)
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We present a formal treatment of multisets (that arise when duplicates are not eliminated) and aggregate operators for deductive and relational databases. We define the semantics rigorously and extend the magicsets technique to programs containing multisets and aggregates. The work presented here is an important step in demonstrating the applicability of the magicsets technique for optimizing queries in commercial query languages such as SQL. 1 Introduction Previous treatments of Datalog and proposed extensions have treated a program as a collection of definitions of sets of facts (tuples). On the other hand, commercial query languages such as SQL typically support the definition of sets and multisets of tuples, and provide aggregate operators such as SUM and COUNT over sets and multisets. The ability to deal with multisets Part of this work was done at the IBM Almaden Research Center. Work at Stanford was supported by an NSF grant IRI87 22886, an Air Force grant AFOSR880266...
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 52 (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 ...
Modeling Multidimensional Databases, Cubes and Cube Operations
 In Proc. of the 10th SSDBM Conference
, 1998
"... OnLine Analytical Processing (OLAP) is a trend in database technology, which was recently introduced and has attracted the interest of a lot of research work. OLAP is based on the multidimensional view of data, supported either by multidimensional databases (MOLAP) or relational engines (ROLAP). ..."
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Cited by 48 (5 self)
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OnLine Analytical Processing (OLAP) is a trend in database technology, which was recently introduced and has attracted the interest of a lot of research work. OLAP is based on the multidimensional view of data, supported either by multidimensional databases (MOLAP) or relational engines (ROLAP).
The Power of Languages for the Manipulation of Complex Values
 VLDB Journal
, 1995
"... Abstract. Various models and languages for describing and manipulating hierarchically structured data have been proposed. Algebraic, calculusbased, and logicprogramming oriented languages have all been considered. This article presents a general model for complex values (i.e., values with hierarc ..."
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Cited by 48 (0 self)
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Abstract. Various models and languages for describing and manipulating hierarchically structured data have been proposed. Algebraic, calculusbased, and logicprogramming oriented languages have all been considered. This article presents a general model for complex values (i.e., values with hierarchical structures), and languages for it based on the three paradigms. The algebraic language generalizes those presented in the literature; it is shown to be related to the functional style of programming advocated by Backus (1978). The notion of domain independence (from relational databases) is defined, and syntactic restrictions (referred to as safety conditions) on calculus queries are formulated to guarantee domain independence. The main results are: The domainindependent calculus, the safe calculus, the algebra, and the logicprogramming oriented language have equivalent expressive power. In particular, recursive queries, such as the transitive closure, can be expressed in each of the languages. For this result, the algebra needs the powerset operation. A more restricted version of safety is presented, such that the restricted safe calculus is equivalent to the algebra without the powerset. The results are extended to the case where arbitrary functions and predicates are used in the languages. Key Words. Database, query language, complex value, complex object, database model.
Deciding Containment for Queries with Complex Objects and Aggregations
, 1997
"... We address the problem of query containment and query equivalence for complex objects. We show that for a certain conjunctive query language for complex objects, query containment and weak query equivalence are decidable. Our results have two consequences. First, when the answers of the two queries ..."
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Cited by 41 (5 self)
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We address the problem of query containment and query equivalence for complex objects. We show that for a certain conjunctive query language for complex objects, query containment and weak query equivalence are decidable. Our results have two consequences. First, when the answers of the two queries are guaranteed not to contain empty sets, then weak equivalence coincides with equivalence, and our result answers partially an open problem about the equivalence of nest; unnest queries for complex objects [GPG90]. Second, we derive an NPcomplete algorithm for checking the equivalence of certain conjunctive queries with grouping and aggregates. Our results rely on a translation of the containment and equivalence conditions for complex objects into novel conditions on conjunctive queries, which we call simulation and strong simulation. These conditions are more complex than containment of conjunctive queries, because they involve arbitrary numbers of quantifier alternations. We prove that c...
Some Properties of Query Languages for Bags
 IN PROCEEDINGS OF 4TH INTERNATIONAL WORKSHOP ON DATABASE PROGRAMMING LANGUAGES
, 1993
"... In this paper we study the expressive power of query languages for nested bags. We define the ambient bag language by generalizing the constructs of the relational language of BreazuTannen, Buneman and Wong, which is known to have precisely the power of the nested relational algebra. Relative s ..."
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Cited by 40 (27 self)
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In this paper we study the expressive power of query languages for nested bags. We define the ambient bag language by generalizing the constructs of the relational language of BreazuTannen, Buneman and Wong, which is known to have precisely the power of the nested relational algebra. Relative strength of additional polynomial constructs is studied, and the ambient language endowed with the strongest combination of those constructs is chosen as a candidate for the basic bag language, which is called BQL (Bag Query Language). We prove that achieveing the power of BQL in the relational language amounts to adding simple arithmetic to the latter. We show that BQL has shortcomings of the relational algebra: it can not express recursive queries. In particular, parity test is not definable in BQL. We consider augmenting BQL with powerbag and structural recursion to overcome this deficiency. In contrast to the relational case, where powerset and structural recursion are equivalent...