Constructing GPSJ view graphs

A data warehouse collects and maintains integrated information from heterogeneous data sources for OLAP and decision support. An important task in data warehouse design is the selection of views to materialize, in order to minimize the response time and maintenance cost of generalized project-select-join (GPSJ) queries. We discuss how to construct GPSJ view graphs. GPSJ view graphs are directed acyclic graphs, used to compactly encode and represent different possible ways of evaluating a set of GPSJ queries. Our view graph construction algorithm, GPSJVIEWGRAPHBUILDER, incrementally constructs GPSJ view graphs based on a set of merge rules. We provide a set of merging rules to construct GPSJ view graphs in the presence of duplicate sensitive and insensitive aggregates. The merging algorithm used in GPSJVIEWGRAPH-BUILDER ensures that each node is correctly added to the view graph, and employs the merge rules to ensure that relationships between nodes from different queries are incorporated into the view graph

A Systematic Review and Meta-Analysis of Fecal Contamination and Inadequate Treatment of Packaged Water

<div><p>Background</p><p>Packaged water products provide an increasingly important source of water for consumption. However, recent studies raise concerns over their safety.</p><p>Objectives</p><p>To assess the microbial safety of packaged water, examine differences between regions, country incomes, packaged water types, and compare packaged water with other water sources.</p><p>Methods</p><p>We performed a systematic review and meta-analysis. Articles published in English, French, Portuguese, Spanish and Turkish, with no date restrictions were identified from online databases and two previous reviews. Studies published before April 2014 that assessed packaged water for the presence of <i>Escherichia coli</i>, thermotolerant or total coliforms were included provided they tested at least ten samples or brands.</p><p>Results</p><p>A total of 170 studies were included in the review. The majority of studies did not detect fecal indicator bacteria in packaged water (78/141). Compared to packaged water from upper-middle and high-income countries, packaged water from low and lower-middle-income countries was 4.6 (95% CI: 2.6–8.1) and 13.6 (95% CI: 6.9–26.7) times more likely to contain fecal indicator bacteria and total coliforms, respectively. Compared to all other packaged water types, water from small bottles was less likely to be contaminated with fecal indicator bacteria (OR = 0.32, 95%CI: 0.17–0.58) and total coliforms (OR = 0.10, 95%CI: 0.05, 0.22). Packaged water was less likely to contain fecal indicator bacteria (OR = 0.35, 95%CI: 0.20, 0.62) compared to other water sources used for consumption.</p><p>Conclusions</p><p>Policymakers and regulators should recognize the potential benefits of packaged water in providing safer water for consumption at and away from home, especially for those who are otherwise unlikely to gain access to a reliable, safe water supply in the near future. To improve the quality of packaged water products they should be integrated into regulatory and monitoring frameworks.</p></div