An attribute (or property) is a feature associated with an entity type. At the entity-type level, each attribute has a domain that defines the set of possible values that can be chosen for it (integer, character string, boolean). At the entity level, each attribute has a value compatible with its domain.
Examples of attributes: the age of a person, the code of a supplier, the number of a product.
Type-association: Let's first define an association. An association (or a relationship) is a link between several entities. A type-association (or a type- relationship) is a set of relationships that have the same characteristics. The type-association describes a link between several types-entities. Like feature-types, association-types are defined by using attributes that take their value from associations.
We often use the word association instead of the word type- association, but we must be careful not to confuse the two concepts.
Examples of type-association: The marriage of two people; the transportation of a product to a warehouse; the assignment of an employee to a service.
Examples of association: The marriage of Max and Claudia; the transport of the Tesla Model S to the deposit of NYC; the fact that Paul works in the Marketing department at Explorium.
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