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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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