Abstract
In this paper we propose an extended relational model named Pvtable for representing exclusive disjunctive data ie exactly one of the possible values is trueby associating partial values and variables with attributes While a partial value plays a role as a set of possible values of the represented data item a variable serves as an identier for the true value of this data item Identiers can be used to determine the equirelationship among partial values The relational operators are extended to manipulate Pvtables We show that the setbased query evaluation on Pvtables is sound and complete for queries consisting of extended selection union intersection Cartesian product and join We also show that good algebraic properties are preserved in our model A disjunctive resp conjunctivequery can be replaced by the extended union resp intersectionof the two corresponding subqueries These properties provide a more natural interpretation of queries They also facilitate query decomposition process for optimizing distributed queries The correctness and algebraic properties are not preserved for many other extended models Introduction