| Summary: | 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.
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