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UML and Data Modeling: A Reconciliation by David Hay

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Note that a package in object-oriented language is not the same as a package in some relational database management system products.

The <<id>> stereotype

In an entity/relationship model, a unique identifier distinguishes each instance of an entity class from every other instance of it.

In the object-oriented world, there is no concept of a natural or meaningful identifier. In an object-oriented program, every object in the system is uniquely identified by a generated surrogate key called an object identifier (known as an OID). Indeed, even in entity/relationship models, reference entity classes, like Person, often use surrogate identifiers (like Person ID, in our example). In dependent entity classes, however, it is ...

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