Calculating constraints on relational expression

Klug, Anthony C.

doi:10.1145/320613.320615

Cited by 60 publications

(47 citation statements)

References 7 publications

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“…For a 2k-ary relation r, requiring that r is a function on k-tuples amounts to the constraint on r that the first k columns form a superkey, which is a special kind of functional dependency (FD). Given a conjunctive query q, a set Σ of FDs, and an FD σ, the implied constraint problem that q(I) satisfies σ for every I that satisfies Σ, can be solved by the chase algorithm [2,24]. For first-order queries, the property of always returning a function is undecidable.…”

Section: Update Operationsmentioning

confidence: 99%

On the expressive power of update primitives

Ameloot

Bussche

Waller

2013

Proceedings of the 32nd ACM SIGMOD-SIGACT-SIGAI Symposium on Principles of Database Systems

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The SQL standard offers three primitive operations (insert, delete, and update which is here called modify) to update a relation based on a generic query. This paper compares the expressiveness of programs composed of these three operations, with the general notion of update that simply replaces the content of the relation by the result of a query. It turns out that replacing cannot be expressed in terms of insertions, deletions, and modifications, and neither can modifications be expressed in terms of insertions and deletions. The expressive power gained by if-then-else control flow in programs is investigated as well. Different ways to perform replacing are discussed: using a temporary variable; using the new SQL merge operation; using SQL's data change delta tables; or using queries involving object creation or arithmetic. Finally the paper investigates the power of alternating the different primitives. For example, an insertion followed by a modification cannot always be expressed as a modification followed by an insertion.

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Section: Update Operationsmentioning

confidence: 99%

On the expressive power of update primitives

Ameloot

Bussche

Waller

2013

Proceedings of the 32nd ACM SIGMOD-SIGACT-SIGAI Symposium on Principles of Database Systems

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“…Let s be a schema and e an expression over s. The derivation rules producing new domain equalities on e are as follows (where " " means "derives") (based on [17]): An attribute can be propagated during the query evaluation and a domain equal attributes can be linked after each step of the query. Names of all the attributes along with the propagating and their domain equal attributes are viewed equal, and stored in a list as shown in Table 1.…”

Section: Preliminariesmentioning

confidence: 99%

Annotation Based Query Answer over Inconsistent Database

Tan

Wang

2010

J. Comput. Sci. Technol.

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In this paper, we introduce a concept of Annotation Based Query Answer, and a method for its computation, which can answer queries on relational databases that may violate a set of functional dependencies. In this approach, inconsistency is viewed as a property of data and described with annotations. To be more precise, every piece of data in a relation can have zero or more annotations with it and annotations are propagated along with queries from the source to the output. With annotations, inconsistent data in both input tables and query answers can be marked out but preserved, instead of being filtered in most previous work. Thus this approach can avoid information loss, a vital and common deficiency of most previous work in this area. To calculate query answers on an annotated database, we propose an algorithm to annotate the input tables, and redefine the five basic relational algebra operations (selection, projection, join, union and difference) so that annotations can be correctly propagated as the valid set of functional dependency changes during query processing. We also prove the soundness and completeness of the whole annotation computing system. Finally, we implement a prototype of our system, and give some performance experiments, which demonstrate that our approach is reasonable in running time, and excellent in information preserving.

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“…We obtain the answer using this algorithm by checking for validity of a certain functional dependency. This can be done by applying the result of [53], which is based on a chase technique [63] ( [53] contains a further development of the results in [51]). Examples of both approaches can be found in [60].…”

Section: Query Optimizationmentioning

confidence: 99%

High Level Efficiency in Database Languages

Larsen¹

1993

DPB

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PrefaceThe subject of this Ph.D. thesis is the design and implementation of database languages. The thesis consists of five articles [16,57,59,60,61] and this survey paper. In [61], a new query language design is proposed. The expressive power of the language is determined in [57] and all reasonable extensions are considered. In [59,60], we focus on the optimization issue of avoiding unnecessary sorting of relations. The results in these papers are directly applicable to any algebra-based query language. In addition to the query language part, a database system also has to offer update facilities. The theory of standard tuple based updates is quite well developed in the sequential case. In [16], we discuss a new concurrent implementation of balanced search trees for that purpose.This survey paper describes the results in the papers which form the thesis, and relates these results to each other and to the area in a broader sense than is customary in the introductions of individual papers. The paper is intended to be read in combination with the papers on which it is based.The last section of this survey paper is a summary in Danish.

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Calculating constraints on relational expression

Cited by 60 publications

References 7 publications

On the expressive power of update primitives

On the expressive power of update primitives

Annotation Based Query Answer over Inconsistent Database

High Level Efficiency in Database Languages

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