148 research outputs found
Advance of the Access Methods
The goal of this paper is to outline the advance of the access methods in the last ten years as well as
to make review of all available in the accessible bibliography methods
Distribution Policies for Datalog
Modern data management systems extensively use parallelism to speed up query processing over massive volumes of data. This trend has inspired a rich line of research on how to formally reason about the parallel complexity of join computation. In this paper, we go beyond joins and study the parallel evaluation of recursive queries. We introduce a novel framework to reason about multi-round evaluation of Datalog programs, which combines implicit predicate restriction with distribution policies to allow expressing a combination of data-parallel and query-parallel evaluation strategies. Using our framework, we reason about key properties of distributed Datalog evaluation, including parallel-correctness of the evaluation strategy, disjointness of the computation effort, and bounds on the number of communication rounds
Histogram techniques for cost estimation in query optimization.
Yu Xiaohui.Thesis (M.Phil.)--Chinese University of Hong Kong, 2001.Includes bibliographical references (leaves 98-115).Abstracts in English and Chinese.Chapter 1 --- Introduction --- p.1Chapter 2 --- Related Work --- p.6Chapter 2.1 --- Query Optimization --- p.6Chapter 2.2 --- Query Rewriting --- p.8Chapter 2.2.1 --- Optimizing Multi-Block Queries --- p.8Chapter 2.2.2 --- Semantic Query Optimization --- p.13Chapter 2.2.3 --- Query Rewriting in Starburst --- p.15Chapter 2.3 --- Plan Generation --- p.16Chapter 2.3.1 --- Dynamic Programming Approach --- p.16Chapter 2.3.2 --- Join Query Processing --- p.17Chapter 2.3.3 --- Queries with Aggregates --- p.23Chapter 2.4 --- Statistics and Cost Estimation --- p.24Chapter 2.5 --- Histogram Techniques --- p.27Chapter 2.5.1 --- Definitions --- p.28Chapter 2.5.2 --- Trivial Histograms --- p.29Chapter 2.5.3 --- Heuristic-based Histograms --- p.29Chapter 2.5.4 --- V-Optimal Histograms --- p.32Chapter 2.5.5 --- Wavelet-based Histograms --- p.35Chapter 2.5.6 --- Multidimensional Histograms --- p.35Chapter 2.5.7 --- Global Histograms --- p.37Chapter 3 --- New Histogram Techniques --- p.39Chapter 3.1 --- Piecewise Linear Histograms --- p.39Chapter 3.1.1 --- Construction --- p.41Chapter 3.1.2 --- Usage --- p.43Chapter 3.1.3 --- Error Measures --- p.43Chapter 3.1.4 --- Experiments --- p.45Chapter 3.1.5 --- Conclusion --- p.51Chapter 3.2 --- A-Optimal Histograms --- p.54Chapter 3.2.1 --- A-Optimal(mean) Histograms --- p.56Chapter 3.2.2 --- A-Optimal(median) Histograms --- p.58Chapter 3.2.3 --- A-Optimal(median-cf) Histograms --- p.59Chapter 3.2.4 --- Experiments --- p.60Chapter 4 --- Global Histograms --- p.64Chapter 4.1 --- Wavelet-based Global Histograms --- p.65Chapter 4.1.1 --- Wavelet-based Global Histograms I --- p.66Chapter 4.1.2 --- Wavelet-based Global Histograms II --- p.68Chapter 4.2 --- Piecewise Linear Global Histograms --- p.70Chapter 4.3 --- A-Optimal Global Histograms --- p.72Chapter 4.3.1 --- Experiments --- p.74Chapter 5 --- Dynamic Maintenance --- p.81Chapter 5.1 --- Problem Definition --- p.83Chapter 5.2 --- Refining Bucket Coefficients --- p.84Chapter 5.3 --- Restructuring --- p.86Chapter 5.4 --- Experiments --- p.91Chapter 6 --- Conclusions --- p.95Bibliography --- p.9
Model Reka Bentuk Konseptual Operasian Storan Data Bagi Aplikasi Kepintaran Perniagaan
The development of business intelligence (BI) applications, involving of data sources, Data Warehouse (DW), Data Mart (DM) and Operational Data Store (ODS), imposes a major challenge to BI developers. This is mainly due to the lack of established models, guidelines and techniques in the development process as compared to system development in the discipline of software engineering. Furthermore, the present BI applications emphasize on the development of strategic information in contrast to operational and tactical. Therefore, the main aim of this study is to propose a conceptual design model for BI applications using ODS (CoDMODS). Through expert validation, the proposed conceptual design model that was developed by means of design science research approach, was found to satisfy nine quality model dimensions, which are, easy to understand, covers clear steps, is relevant and timeless, demonstrates flexibility, scalability, accuracy, completeness and consistency. Additionally, the two prototypes that were developed based on CoDMODS for water supply service (iUBIS) and telecommunication maintenance (iPMS) recorded a high usability average min value of 5.912 using Computer System Usability Questionnaire (CSUQ) instrument. The outcomes of this study, particularly the proposed model, contribute to the analysis and design method for the development of the operational and tactical information in BI applications. The model can be referred as guidelines by BI developers. Furthermore, the prototypes that were developed in the case studies can assist the organizations in using quality information for business operations
A data complexity and rewritability tetrachotomy of ontology-mediated queries with a covering axiom
Aiming to understand the data complexity of answering conjunctive queries mediated by an axiom stating that a class is covered by the union of two other classes, we show that deciding their first-order rewritability is PSPACE-hard and obtain a number of sufficient conditions for membership in AC0, L, NL, and P. Our main result is a complete syntactic AC0/NL/P/CONP tetrachotomy of path queries under the assumption that the covering classes are disjoint
Magic Sets for Disjunctive Datalog Programs
In this paper, a new technique for the optimization of (partially) bound
queries over disjunctive Datalog programs with stratified negation is
presented. The technique exploits the propagation of query bindings and extends
the Magic Set (MS) optimization technique.
An important feature of disjunctive Datalog is nonmonotonicity, which calls
for nondeterministic implementations, such as backtracking search. A
distinguishing characteristic of the new method is that the optimization can be
exploited also during the nondeterministic phase. In particular, after some
assumptions have been made during the computation, parts of the program may
become irrelevant to a query under these assumptions. This allows for dynamic
pruning of the search space. In contrast, the effect of the previously defined
MS methods for disjunctive Datalog is limited to the deterministic portion of
the process. In this way, the potential performance gain by using the proposed
method can be exponential, as could be observed empirically.
The correctness of MS is established thanks to a strong relationship between
MS and unfounded sets that has not been studied in the literature before. This
knowledge allows for extending the method also to programs with stratified
negation in a natural way.
The proposed method has been implemented in DLV and various experiments have
been conducted. Experimental results on synthetic data confirm the utility of
MS for disjunctive Datalog, and they highlight the computational gain that may
be obtained by the new method w.r.t. the previously proposed MS methods for
disjunctive Datalog programs. Further experiments on real-world data show the
benefits of MS within an application scenario that has received considerable
attention in recent years, the problem of answering user queries over possibly
inconsistent databases originating from integration of autonomous sources of
information.Comment: 67 pages, 19 figures, preprint submitted to Artificial Intelligenc
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