On the Kolmogorov expressive power of boolean query languages

Web is characterized by a huge amount of very heterogeneous data sources, that differ both in media support and format representation. In this scenario, there is the need of an integrating approach for querying heterogeneous Web documents. To this purpose, XML can play an important role since it is becoming a standard for data representation and exchange over the Web. Due to its flexibility, XML is currently being used as an interface language over the Web, by which (part of) document sources are represented and exported. Under this assumption, the problem of querying heterogeneous sources can be reduced to the problem of querying XML data sources. In this chapter, we first survey the most relevant query languages for XML data proposed both by the scientific community and by standardization committees, e.g., W3C, mainly focusing on their expressive power. Then, we investigate how typical Information Retrieval concepts, such as ranking, similarity-based search, and profile-based search, can be applied to XML query languages. Commercial products based on the considered approaches are then briefly surveyed. Finally, we conclude the chapter by providing an overview of the most promising research trends in the fields.

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Pseudo-finite homogeneity and saturation

Journal of Symbolic Logic ◽

10.2307/2586806 ◽

1999 ◽

Vol 64 (4) ◽

pp. 1689-1699 ◽

Cited By ~ 5

Author(s):

Jörg Flum ◽

Martin Ziegler

Keyword(s):

Expressive Power ◽

Query Languages ◽

Stable Theory ◽

Finite Cover ◽

Database Query ◽

Homogeneity Property ◽

Finite States

AbstractWhen analyzing database query languages a roperty, of theories, the pseudo-finite homogeneity property, has been introduced and applied (cf. [3]). We show that a stable theory has the pseudo-finite homogeneity property just in case its expressive power for finite states is bounded. Moreover, we introduce the corresponding pseudo-finite saturation property and show that a theory fails to have the finite cover property if and only if it has the pseudo-finite saturation property.

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From Relation Algebra to Semi-join Algebra: An Approach to Graph Query Optimization

The Computer Journal ◽

10.1093/comjnl/bxaa031 ◽

2020 ◽

Author(s):

Jelle Hellings ◽

Catherine L Pilachowski ◽

Dirk Van Gucht ◽

Marc Gyssens ◽

Yuqing Wu

Keyword(s):

Query Optimization ◽

Relation Algebra ◽

Expressive Power ◽

Query Languages ◽

Query Evaluation ◽

Relation Algebras ◽

Ordered Trees ◽

Graph Query ◽

Study Techniques ◽

The Relationship

Abstract Many graph query languages rely on composition to navigate graphs and select nodes of interest, even though evaluating compositions of relations can be costly. Often, this need for composition can be reduced by rewriting toward queries using semi-joins instead, resulting in a significant reduction of the query evaluation cost. We study techniques to recognize and apply such rewritings. Concretely, we study the relationship between the expressive power of the relation algebras, which heavily rely on composition, and the semi-join algebras, which replace composition in favor of semi-joins. Our main result is that each fragment of the relation algebras where intersection and/or difference is only used on edges (and not on complex compositions) is expressively equivalent to a fragment of the semi-join algebras. This expressive equivalence holds for node queries evaluating to sets of nodes. For practical relevance, we exhibit constructive rules for rewriting relation algebra queries to semi-join algebra queries and prove that they lead to only a well-bounded increase in the number of steps needed to evaluate the rewritten queries. In addition, on sibling-ordered trees, we establish new relationships among the expressive power of Regular XPath, Conditional XPath, FO-logic and the semi-join algebra augmented with restricted fixpoint operators.

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