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Comparative Study of Ordered and Covering Information Systems

Wang C., He Q., Chen D., Hu Q.

Fundamenta Informaticae

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2013

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Vol. 123, nr 3

351--363

EN

Covering information systems and ordered information systems are two important types of information systems. In this paper the relationships between covering information systems and ordered information systems are first examined, and it is proved that these two types of information systems are isomorphic under given conditions and can be equivalently transformed into each other. Then, the approach to attribute reduction in ordered information systems is proposed. Based on the isomorphism and equivalence of transformation, the method of attribute reduction in a covering information system can be directly obtained according to the reduction approach in an ordered in- formation system. A practical example is employed to show that the proposed method is an effective technique to deal with complex data sets.

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Three-machine flowshop scheduling problem to minimize total completion time with bounded setup and processing times

Allahverdi A.

Decision Making in Manufacturing and Services

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2007

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Vol. 1, no. 1-2

5-23

EN

The three-machine flowshop scheduling problem to minimize total completion time is studied where setup times are treated as separate from processing times. Setup and processing times of all jobs on all machines are unknown variables before the actual occurrence of these times. The lower and upper bounds for setup and processing times of each job on each machine is the only information that is available. In such a scheduling environment, there may not exist a unique schedule that remains optimal for all possible realizations of setup and processing times. Therefore, it is desired to obtain a set of dominating schedules (which dominate all other schedules) if possible. The objective for such a scheduling environment is to reduce the size of dominating schedule set. We obtain global and local dominance relations for a three-machine flowshop scheduling problem. Furthermore, we illustrate the use of dominance relations by numerical examples and conduct computational experiments on randomly generated problems to measure the effectiveness of the developed dominance relations. The computational experiments show that the developed dominance relations are quite helpful in reducing the size of dominating schedules.

3

Long-term changes and spatial variability of mollusc communsities in selected habitats within the dam reservoir (Włocławek Reservoir, Vistula River, Central Poland)

Jurkiewicz-Karnkowska E., Żbikowski J.

Polish Journal of Ecology

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2004

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Vol. 52, nr 4

491-503

EN

The studies on long-term and spatial variability in dominance pattern and abundance of malacofauna in selected habitats of the Włocławek Reservoir (Central Poland) were made in relation to environmental factors. Abundant and relatively rich in species malacocenoses were dominated by Sphaerium corneum. Malacofauna of shallow biotopes was characterized by higher species richness and lower abundance than molluscs inhabiting the old river bed. Eutrophication, turbidity and transformation of bottom sediments are likely to be the most important factors influencing changes in malacocenoses.