| Summary: | 碩士 === 國立中正大學 === 資訊工程研究所 === 82 === We present an object-oriented data model which includes an
algebra of classes that is closed under the operations of
union, intersection, difference, selection, projection, and
join. The closure property means that any set expression has a
well- defined set of elements with a specific set of required
attributes with well-defined domains, and which satisfy a well-
defined invariant. Therefore, each class also has a definite
set of ISA parent classes, ISA subclasses and inherited slots
and methods with well-defined domains. The involving the
union, intersection, difference, select, project, and join
operators. That is, the set expression is moved into its
correct location in the ISA hierarchy, depending on the
invariant which is computed for that expression.
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