Pv-table -- A Representation System for Exclusive Disjunctive Data

• Main Authors: Chiu, Jui-Shang, 邱瑞山
• Other Authors: Arbee L.P. Chen
• Format: Others
• Language: zh-TW
• Published: 1995
• Online Access: http://ndltd.ncl.edu.tw/handle/b5e3yy

博士 === 國立清華大學 === 資訊科學學系 === 83 === In this dissertation, we propose an extended relational model, named Pv-table, for representing exclusive disjunctive data by associating partial values and variables with attributes. While a partial value denotes the set of possible values, a variable serves as an identifier for the true value of the data item. In addition, variables can be used to preserve distinctness of values, the equi- relationship of values, and dependency information in the operations. The relational operators are extended to manipulate Pv-tables. We show that the set-based query evaluation on Pv-tables is sound and complete for queries consisting of extended selection, union, intersection, Cartesian product and join. We also show that useful algebraic properties in conventional relational models are preserved in our model. These properties are not preserved for many other extended models. Pv-table is further generalized for the ability to correctly support the difference operator which is mandatory in database updates and dependency enforcement. A set of generalized relational operators is defined, so that a unified solution to queries, updates and constraint enforcement can be obtained. The semantic correctness is established. By variable sets, tuples may be related with certain relationships, namely disjunctive relationship and join relationship. Three kinds of tuple sets are classified according to these relationships; each possesses an important property, namely co-exist, co- nonempty and co-instance. Based on these properties, the interpretation of Pv-tables can be formalized in a semantically meaningful way. Also, the redundant and mergeable tuples can be identified. After removing and merging tuples accordingly, a more concise Pv-table can thus provide a better understanding of the query result.