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Repetitions and permutations of columns in the semijoin algebra

Dirk Leinders, Jan Van Den Bussche (2009)

RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications

Codd defined the relational algebra [E.F. Codd, Communications of the ACM 13 (1970) 377–387; E.F. Codd, Relational completeness of data base sublanguages, in Data Base Systems, R. Rustin, Ed., Prentice-Hall (1972) 65–98] as the algebra with operations projection, join, restriction, union and difference. His projection operator can drop, permute and repeat columns of a relation. This permuting and repeating of columns does not really add expressive power to the relational algebra. Indeed, using the...

Repetitions and permutations of columns in the semijoin algebra

Dirk Leinders, Jan Van Den Bussche (2008)

RAIRO - Theoretical Informatics and Applications

Codd defined the relational algebra [E.F. Codd, Communications of the ACM13 (1970) 377–387; E.F. Codd, Relational completeness of data base sublanguages, in Data Base Systems, R. Rustin, Ed., Prentice-Hall (1972) 65–98] as the algebra with operations projection, join, restriction, union and difference. His projection operator can drop, permute and repeat columns of a relation. This permuting and repeating of columns does not really add expressive power to the relational algebra. Indeed, ...

Representación de datos de conjuntos aproximados mediante diagramas de decisión binarios.

Alex Muir, Ivo Düntsch, Günther Gediga (2004)

RACSAM

A new information system representation, which inherently represents indiscernibility is presented. The basic structure of this representation is a Binary Decision Diagram. We offer testing results for converting large data sets into a Binary Decision Diagram Information System representation, and show how indiscernibility can be efficiently determined. Furthermore, a Binary Decision Diagram is used in place of a relative discernibility matrix to allow for more efficient determination of the discernibility...

Rough membership functions: a tool for reasoning with uncertainty

Z. Pawlak, A. Skowron (1993)

Banach Center Publications

A variety of numerical approaches for reasoning with uncertainty have been investigated in the literature. We propose rough membership functions, rm-functions for short, as a basis for such reasoning. These functions have values in the interval [0,1] and are computable on the basis of the observable information about the objects rather than on the objects themselves. We investigate properties of the rm-functions. In particular, we show that our approach is intensional with respect to the class of...

Rough modeling - a bottom-up approach to model construction

Terje Loken, Jan Komorowski (2001)

International Journal of Applied Mathematics and Computer Science

Traditional data mining methods based on rough set theory focus on extracting models which are good at classifying unseen obj-ects. If one wants to uncover new knowledge from the data, the model must have a high descriptive quality-it must describe the data set in a clear and concise manner, without sacrificing classification performance. Rough modeling, introduced by Kowalczyk (1998), is an approach which aims at providing models with good predictive emphand descriptive qualities, in addition to...

Search trees and bubble memories

Philippe Flajolet, Thomas Ottmann, Derick Wood (1985)

RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications

Seasonal time-series imputation of gap missing algorithm (STIGMA)

Eduardo Rangel-Heras, Pavel Zuniga, Alma Y. Alanis, Esteban A. Hernandez-Vargas, Oscar D. Sanchez (2023)

Kybernetika

This work presents a new approach for the imputation of missing data in weather time-series from a seasonal pattern; the seasonal time-series imputation of gap missing algorithm (STIGMA). The algorithm takes advantage from a seasonal pattern for the imputation of unknown data by averaging available data. We test the algorithm using data measured every 10 minutes over a period of 365 days during the year 2010; the variables include global irradiance, diffuse irradiance, ultraviolet irradiance, and temperature,...

Sender-equivocable encryption schemes secure against chosen-ciphertext attacks revisited

Zhengan Huang, Shengli Liu, Baodong Qin, Kefei Chen (2015)

International Journal of Applied Mathematics and Computer Science

Fehr et al. (2010) proposed the first sender-equivocable encryption scheme secure against chosen-ciphertext attacks (NCCCA) and proved that NC-CCA security implies security against selective opening chosen-ciphertext attacks (SO-CCA). The NC-CCA security proof of the scheme relies on security against substitution attacks of a new primitive, the “crossauthentication code”. However, the security of the cross-authentication code cannot be guaranteed when all the keys used in the code are exposed. Our...

Space-efficient parallel merging

J. Katajainen, C. Levcopoulos, O. Petersson (1993)

RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications

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