CSC 4402 20091021

CSC 4402 20091021 - If a relationship is one-to-many then...

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CSC 4402 10/21/2009 Page 1 of 1 Chapter 6 – E-R design process (cont’d) Main concepts: Entities o Instance is an individual object o Type or set the entity belongs to Relationships o Instance o Set A relationship set is a mathematical relation among n ≥2 entities, each taken from entity sets {( e 1 , e 2 , … e n ) | e 1 E 1 , e 2 E 2 , …, e n E n }where ( e 1, e 2, …, en ) is a relationship. Figure 1 – Example of an attribute in a relation for students/courses
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Unformatted text preview: If a relationship is one-to-many, then we could put the attribute with the entity on the many side. For a one-to-many relationship, the candidate key in the relationship set is the candidate key from the many side. Total/partial participation – example: in the banking example. If every customer must have a loan, this is total participation; otherwise it is partial participation....
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