On Indiscernibility Relations for Missing Attribute Values

Rafal Latkowski

rlatkows@mimuw.edu.pl
Institute of Computer Science, Warsaw University
ul. Banacha 2, 02--097 Warsaw, Poland

Abstract

The indiscernibility relation is a fundamental concept of the rough set 
theory. The original definition of the indiscernibility relation,
thus the rough set theory, does not capture the situation where some of
the attribute values are missing. This paper tries to enhance former works
by proposing an individual treatment of missing values at the attribute
or value level. The main assumption of the theses presented in this paper
considers that not all missing values are semantically equal. We propose
two different approaches to create an individual indiscernibility relation
for a particular information system. The first relation assumes variable,
but fixed semantics of missing attribute values in different columns. The
second relation assumes different semantics of missing attribute values,
although this variability is limited with expressive power of formulas
utilizing descriptors.