题目内容
An ____________ is an object, which can be uniquely distinguished from other objects.
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The set of all entities of the same type and relationships of the same type are termed as ____________ ____________ and ____________ ____________ respectively.
Entities and relationships are to be distinguished using the concept of ____________ ____________.
Object-based logical models are used for describing data at the ____________ and ____________ levels.
The three widely used record-based logical models are ____________ Model、____________ Model and ____________ Model.
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