Handling Redundancies for Disjunctive Information with Exclusive-or Semantics

The relational database model has been proven to be a very useful model in database management systems and has been widely applied [4]. The inherence of the relational database model is effective for precise and unambiguous data. However, realworld applications often involve incomplete information. In this study, a logical fuzzy relational database model was proposed to accommodate incomplete information into the relational model. Incomplete information means that instead of having a single value for an attribute, we have a subset of values for the corresponding attribute [9]. The first attempt to extend the relational model was null values. Null values are unknown or nonapplicable values [3, 8, 9, 14]. Another attempt is to introduce disjunctive information into the relational database model [8, 10]. Following the closure assumptions in the presence of disjunctive information, some authors have been exploring the field of disjunctive logic programming [12]. Codd [3] used maybe tuples for manipulating existential null that exist in relational databases. Since we consider disjunctive information in this paper, maybe information [9] might be obtained from disjunctive information in two cases. One is when a database is update, and the other is when relational operators are applied to a database. Consider a relation containing the information about the age of employee and suppose that we want to represent the following disjunctive information in the relation, “John is either 28 or 30