A new approach to soft sets, soft multisets and their properties

Abstract

Soft set theory is a new mathematical approach to vagueness introduced by Molodtsov (1999). This is a parameterised family of subsets defined over a universal set using a set of parameters. In this paper, we introduce the notion of characteristic function of a soft set, which helps us in defining the basic operations on soft sets concisely; several concepts associated with it efficiently and make the proofs of properties more elegant. We rectified the definition of complement of a soft set and the earlier definition of complement is now called as the negation of a multiset. Like the crisp multisets, soft multiset is a notion which allows multiple occurrences of elements in a model. So far, more than one attempt has been made to define this concept. Out of these the one put forth by Majumdar (2012) is the most appropriate one and so we use it in this paper. We redefined the concepts of complement of a soft multiset, null soft multiset and absolute soft multiset and introduced many operations on soft multisets like the union and intersection of soft multisets and cardinality of soft multisets. Also, we defined the concepts of addition and deletion of elements from a soft multiset. Two new operations, called the addition and difference of two soft multisets are introduced. We establish several properties of these operations on soft multisets including the De Morgan's Law, associative and distributive properties. A real life example is being used for the purpose of illustration of the notions and concepts.