A universal relation data model with semantic constructs
Chang, Tzy-hey H.
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This thesis describes a modularized universal relation data model, called URMSC (Universal Relation Data Model with Semantic Constructs). This model incorporates concepts from the semantic data model, such as the notions of entities, aggregation abstractions and generalization/specialization abstractions, into the universal relation data model. These semantic constructs allow us to reduce multiple paths among relation and allow us to loosen some of the constraints that the URM imposes. Consequently, a larger class of queries can be interpreted unambiguously. Modules are defined by aggregation hierarchies. Each module must satisfy the local unique name and attr£bute correlat£on assumptions. The former requires the uniqueness of attribute names on each individual module instead of the entire database scheme, to reduce the number of attribute renamings. The latter is used to disambiguate a query interpretation when there are duplicate attribute names in a database. In a universal relation system, data retrieval queries are expressed by mentioning only the attribute names of interest and their values. We extend this idea to the notion of database update. By taking advantage of the semantic constructs of the model, we provide criteria that guarantee unambiguous interpretation of update requests.
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