Recently, Wang et al. discussed the properties of fuzzy information systems
under homomorphisms in the paper [C. Wang, D. Chen, L. Zhu, Homomorphisms
between fuzzy information systems, Applied Mathematics Letters 22 (2009)
1045-1050], where homomorphisms are based upon the concepts of consistent
functions and fuzzy relation mappings. In this paper, we classify consistent
functions as predecessor-consistent and successor-consistent, and then proceed
to present more properties of consistent functions.
This note is an amendment to a paper by Wang et al. [C. Wang, C. Wu, D. Chen,
Q. Hu, and C. Wu, Communicating between information systems, Information
Sciences 178 (2008) 3228-3239]. To study the communication between two
information systems, Wang et al. proposed two concepts of type-1 and type-2
consistent functions. Some good properties of consistent functions and induced
relation mappings have been investigated there. In this paper, we provide an
improvement of the aforementioned work by disclosing the symmetric relationship
between type-1 and type-2 consistent functions.
In Pawlak's rough set theory, each rough set is approximated by a pair of
lower and upper approximations. To measure numerically the roughness of an
approximation, Pawlak introduced a quantitative measure of roughness by using
the ratio of the cardinalities of the lower and upper approximations. Although
the roughness measure is effective, it has the drawback of not being strictly
monotonic with respect to the standard ordering on partitions. Recently, some
improvements have been made by taking into account the granularity of
partitions.
Rough set theory, a mathematical tool to deal with vague concepts, has
originally described the indiscernibility of elements by equivalence relations.
Covering rough sets are a natural extension of classical rough sets by relaxing
the partitions arising from equivalence relations to covers. Recently, some
topological concepts such as neighborhood have been applied to covering rough
sets. In this paper, we further investigate the covering rough sets based on
neighborhoods by approximation operations.
To capture the uncertainty of information or knowledge in information
systems, various information granulations, also known as knowledge
granulations, have been proposed. Recently, several axiomatic definitions of
information granulation have been introduced. In this paper, we try to improve
these axiomatic definitions and give a universal construction of information
granulation by relating information granulations with a class of functions of
multiple variables. We show that the improved axiomatic definition has some
concrete information granulations in the literature as instances.