| Rough Set Theory is an attempt to tackling the problem of imperfect knowledge .In rough set theory ,we assume that with every object some information is associated and objects can be "seen" through the accessible information only. Hence, object with the same information can not be discerned and appear as the same. This results in, that indiscernible objects of the universe form clusters of indistinguishable object.The concept of factor space, proposed by WangPeiZhuang. In 1982, he delivered thesis about factor space formally. Now, there are many aspect that is one of factor space, such as, the state space of modern control theory, feature space and parameter space in model identify.Rough set theory and factor space are all applied worldly. The partition determined by equivalence relation is the same as knowledge in rough set theory, that is, knowledge is regarded as a partition of data. Any set of all indiscernible objects is called an elementary concepts. The research objects is described by a multi-attribute set. With every object, there has a value describing the attribute. Object, attribute and attribute-value are three element to the problem of decision. Data are often presented as information tables, column of which are labelled by attributes, rows by objects and entries of the table are attribute-values. So the table is the database of rough set theory. However, there have relation between factor space and database. In the article, we argued the relation.Sometimes, the poor database is very common when you use them. So the demanding database must be effective collection. It must be done that collecting and arrangement before acquiring knowledge. However, the acquired data may not fit to acquire knowledge directly. If the information is default, we must fill it. Now there are many methods tofill default. In this article, tolerance relation is applied to fil default in decision table. Practice prove the efficiency of the method. |
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