A sound and sometimes complete query evaluation algorithm for relational databases with null values

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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A Query Language for Workflow Logs

ACM Transactions on Management Information Systems ◽

10.1145/3482968 ◽

2022 ◽

Vol 13 (2) ◽

pp. 1-28

Author(s):

Yan Tang ◽

Weilong Cui ◽

Jianwen Su

Keyword(s):

Business Process ◽

Evaluation Method ◽

Ad Hoc ◽

Query Language ◽

Cost Model ◽

Formal Semantics ◽

Control Flow ◽

Query Evaluation ◽

Evaluation Algorithm ◽

Laws And Policies

A business process (workflow) is an assembly of tasks to accomplish a business goal. Real-world workflow models often demanded to change due to new laws and policies, changes in the environment, and so on. To understand the inner workings of a business process to facilitate changes, workflow logs have the potential to enable inspecting, monitoring, diagnosing, analyzing, and improving the design of a complex workflow. Querying workflow logs, however, is still mostly an ad hoc practice by workflow managers. In this article, we focus on the problem of querying workflow log concerning both control flow and dataflow properties. We develop a query language based on “incident patterns” to allow the user to directly query workflow logs instead of having to transform such queries into database operations. We provide the formal semantics and a query evaluation algorithm of our language. By deriving an accurate cost model, we develop an optimization mechanism to accelerate query evaluation. Our experiment results demonstrate the effectiveness of the optimization and achieves up to 50× speedup over an adaption of existing evaluation method.

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The Fixpoint Bounded-Variable Queries are PSPACE-Complete

BRICS Report Series ◽

10.7146/brics.v3i41.20023 ◽

1996 ◽

Vol 3 (41) ◽

Cited By ~ 1

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.

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Normalization and Translation of XQuery

Advanced Applications and Structures in XML Processing ◽

10.4018/978-1-61520-727-5.ch013 ◽

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.

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