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Describe what relationships represent in an ER model and provide examples of unary, binary, and ternary relationships

Describe what relationships represent in an ER model and provide examples of unary, binary, and ternary relationships

Answers

kelvin
Relationship is a set of meaningful associations among entities. As with entities, each association should be uniquely identifiable within the set. A uniquely identifiable association is called a relationship occurrence. Each relationship is given a name that describes its function. For example, the Actor entity is associated with the Role entity through a relationship called Plays, and the Role entity is associated with the Video entity through a relationship called Features.

The entities involved in a particular relationship are referred to as participants. The number of participants in a relationship is called the degree and indicates the number of entities involved in a relationship. A relationship of degree one is called unary, which is commonly referred to as a recursive relationship. A unary relationship describes a relationship where the same entity participates more than once in different roles. An example of a unary relationship is Supervises, which represents an association of staff with a supervisor where the supervisor is also a member of staff. In other words, the Staff entity participates twice in the Supervises relationship; the first participation as a supervisor, and the second participation as a member of staff who is supervised (supervisee). See Figure 7.5 for a diagrammatic representation of the Supervises relationship.
kevowmuchiri answered the question on July 4, 2018 at 16:24

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