Use examples to distinguish between: a. An object type and an entity type b. An object and an entity

QUESTION:

Use examples to distinguish between:

a. An object type and an entity type

b. An object and an entity

c. A property and an attribute 

d. An entity and an entity instance

e. An association and a relationship

f. An object class and an entity class

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SOLUTION:

a. An object type is a named collection of properties that sufficiently describes an actual distinct type of identity. An object type can be tangible (e.g., a vehicle) or intangible (e.g., project). An entity type is a conceptual representation of an object type (e.g., a drawing of a vehicle).

b. An object is an actual occurrence of an object type (e.g., an actual vehicle). An entity is an occurrence of an entity type (i.e., the representation of a vehicle in a VEHICLE data set).

c. A property is a characteristic of an object type, whereas an attribute is a characteristic of an entity type. For example, the measured weight of a person would be termed a property, whereas the weight of the same person as recorded as a numeric value in a database would be termed an attribute.

d. An entity and an entity instance are one and the same. Both refer to an occurrence of an entity type. For example, the record for Anna Li in a STUDENT data set would be termed an entity or entity instance.

e. Associations exist in the real world between object types (e.g., a specific faculty member advises a specific group of students). In the conceptual world, such associations are referred to as relationships between entity types.

f. An object class is a generalization of different related object types that have shared properties. For example, the object types basketball player, baseball player, and football player can be said to belong to the object class athlete. An entity class is a generalization of different related entity types that have shared attributes.

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