Abstract

Nowadays, current trends of universal quantification-based queries are been oriented towards flexible ones (tolerant queries and-or those involving preferences). In this paper, we are interested in universal quantification-like queries dealing with both positive or negative preferences (requirements or prohibitions), considered separately or simultaneously. We have emphasised the improvement of the proposed operator, by designing new variants of the classical Hash-Division algorithm, presented in [1], for dealing with our context. The parallel implementation is also presented, and the issue of answers ranking is dealt with. Computational experiments are carried out in both sequential and parallel versions. They shows the relevance of our approach and demonstrate that the new operator outperforms the conventional one with respect to performance (the gain exceeds a ratio of 40).

Highlights

  • Relational operators including universal quantification are an interesting type of queries

  • We address the performance enhancement of the new operator drawing to the Hash-Division strategy as used in our previous work [14]

  • Hash-Division algorithm is proceeding in three stage: Stage 01: Building the hash-divisor table : during the scan of the divisor table, we insert all divisor tuples into buckets in the hash-divisor table

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Summary

Introduction

Relational operators including universal quantification are an interesting type of queries. They are very useful for many applications, especially in business intelligence applications and in recommendation systems [2]. Universal quantification-like queries are the most complex operators. That is why a lot of research focuses on their implementation, algorithms and optimisation[3]. Universal quantification-like queries are, often, about division or anti-division operators. The division searches elements associated with all members of a set of requirements, while the anti-division aims to find all elements that are associated with none of the members of a set of prohibitions[4]. We are concerned with some relevant issues related to the improvement of queries combining both of required and forbidden associations

The division and anti-division operators
Current trends
Related work and motivation
Main contributions in this paper
Outline of the paper
Review of Hash-Division Algorithm
Review of Flexible Division and Flexible anti-division
Principle
Modelling
Our proposed approach for the mixed query
Strict and gradual Mixed Query
Hash-mixed query: an improvement of the mixed query
Experimentations
Parallel implementation
Conclusion and perspectives
Full Text
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