scholarly journals The Fixpoint Bounded-Variable Queries are PSPACE-Complete

1996 ◽  
Vol 3 (41) ◽  
Author(s):  
Stefan Dziembowski
Keyword(s):  
Upper Bound ◽  
Relational Databases ◽  
Query Evaluation ◽  
Individual Variables

We study complexity of the evaluation of fixpoint bounded-variable<br />queries in relational databases. We exhibit a finite database such<br />that the problem whether a closed fixpoint formula using only 2 individual variables is satisfied in this database is PSPACE-complete. This clarifies the issues raised by Moshe Vardi in [Var95]. We study also the complexity of query evaluation for a number of restrictions of fixpoint logic. In particular we exhibit a sublogic for which the upper bound postulated by Vardi holds.

Normalization and Translation of XQuery

2010 ◽  
pp. 283-307
Author(s):  
Norman May ◽  
Guido Moerkotte
Keyword(s):  
Relational Databases ◽  
Processing Method ◽  
Query Evaluation ◽  
Evaluation Technique ◽  
Good Basis ◽  
Algebra Representation ◽  
Translation Techniques ◽  
Comprehensive Survey ◽  
Algebraic Optimization ◽  
Evaluation Techniques

Early approaches to XQuery processing proposed proprietary techniques to optimize and evaluate XQuery statements. In this chapter, the authors argue for an algebraic optimization and evaluation technique for XQuery as it allows us to benefit from experience gained with relational databases. An algebraic XQuery processing method requires a translation into an algebra representation. While many publications already exist on algebraic optimizations and evaluation techniques for XQuery, an assessment of translation techniques is required. Consequently, they give a comprehensive survey for translating XQuery into various query representations. The authors relate these approaches to the way normalization and translation is implemented in Natix and discuss these two steps in detail. In their experience, their translation method is a good basis for further optimizations and query evaluation.

Error-constrained COUNT query evaluation in relational databases

1991 ◽  
Vol 20 (2) ◽  
pp. 278-287 ◽  
Author(s):  
Wen-Chi Hou ◽  
Gultekin Ozsoyoglu ◽  
Erdogan Dogdu
Keyword(s):  
Relational Databases ◽  
Query Evaluation

Database Principles and Challenges in Text Analysis

2021 ◽  
Vol 50 (2) ◽  
pp. 6-17
Author(s):  
Johannes Doleschal ◽  
Benny Kimelfeld ◽  
Wim Martens
Keyword(s):  
Text Analysis ◽  
Relational Databases ◽  
Query Evaluation ◽  
Text Documents ◽  
Step Process ◽  
Distributed Query ◽  
Recent Advances ◽  
Aggregate Queries ◽  
Technical Challenges ◽  
Query Planning

A common conceptual view of text analysis is that of a two-step process, where we first extract relations from text documents and then apply a relational query over the result. Hence, text analysis shares technical challenges with, and can draw ideas from, relational databases. A framework that formally instantiates this connection is that of the document spanners. In this article, we review recent advances in various research efforts that adapt fundamental database concepts to text analysis through the lens of document spanners. Among others, we discuss aspects of query evaluation, aggregate queries, provenance, and distributed query planning.

scholarly journals XPath bipolar queries and evaluation

2017 ◽  
Vol Volume 27 - 2017 - Special... ◽  
Author(s):  
Maurice Tchoupé Tchendji ◽  
Brice Nguefack
Keyword(s):  
Relational Databases ◽  
Query Evaluation ◽  
Nous Proposons ◽  
Xml Database ◽  
Structural Preferences ◽  
Evaluation Algorithm ◽  
Satisfactory Answer ◽  
Premiere Partie

The concept of bipolar queries (also call preferences queries) emerged in the Relational Databasescommunity, allowing users to get much more relevant responses to their requests, expressed via queries say withpreferences. Such requests usually have two parts: the first is used to express the strict constraints and thesecond, preferences or wishes. Any response to a query with preferences must necessarily satisfy the first partand preferably the latter. However, if there is at least a satisfactory answer of the second part, those satisfyingonly the first part will be excluded from the final result: they are dominated. In this paper, we explore an approachof importation of this concept in a XML Database via XPath language. To do this, we propose PrefSXPathlanguage, an extension of XPath in order to express XPath queries with structural preferences, then we presenta query evaluation algorithm of PrefSXPath using automata Le concept de requêtes bipolaires (on parle aussi de requêtes avec préférences) a émergé dans la communauté des Bases de Données Relationnelles, pour permettre aux utilisateurs d'obtenir des réponses beaucoup plus pertinentes à leurs préoccupations, exprimées via des requêtes dites avec préférences. De telles requêtes ont généralement deux parties : la première permet d'exprimer les contraintes strictes et la seconde, des préférences ou souhaits. Toute réponse à une requête avec préférences doit nécessairement satisfaire la première partie et préférentiellement la seconde. Toutefois, s'il existe au moins une réponse satisfaisant la seconde partie, toutes les réponses ne satisfaisant que la première partie seront exclues du résultat final : elles sont dominées. Dans ce papier, nous explorons une approche d'importation de ce concept dans les Bases de Données XML via le langage XPath. Pour ce faire, nous proposons le langage PrefSXPath, une extension du langage XPath permettant d'exprimer les requêtes XPath avec préférences structurelles, puis, nous présentons un algorithme d'évaluation des requêtes PrefSXPath à l'aide des automates. ABSTRACT. The concept of bipolar queries (also call preferences queries) emerged in the Relational Databases community, allowing users to get much more relevant responses to their requests, expressed via queries say with preferences. Such requests usually have two parts: the first is used to express the strict constraints and the second, preferences or wishes. Any response to a query with preferences must necessarily satisfy the first part and preferably the latter. However, if there is at least a satisfactory answer of the second part, those satisfying only the first part will be excluded from the final result: they are dominated. In this paper, we explore an approach of importation of this concept in a XML Database via XPath language. To do this, we propose PrefSXPath language, an extension of XPath in order to express XPath queries with structural preferences, then we present a query evaluation algorithm of PrefSXPath using automata.

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