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Unformatted text preview: to the entity. The Crow’s Foot notation does not identify multivalued attributes. CAR YEAR CAR LICENSE CAR_VIN CAR CAR MAKE CAR COLOR Implementing Multi‐valued Attributes: Although conceptually, the model can handle M:N relationships and mutivalued attributes, they cannot be implemented in the RDBMS. So, if multivalued attributes exist, the designer must decide two possible course of action: 1. Within the original entity, create several new attributes, one for each component of the original mutivalued attribute. For example, the CAR entity’s attribute CAR_COLOR can be split to create new attributes CAR_TOPCOLOR, CAR_BODYCOLOR and CAR_TRIMCOLOR which are then assigned to the CAR entity. The problem with this approach is that if there are many options for some tuples and not for all tuples, then the values for most of the new attributes is going to be NULL. 2. Create a new entity composed by the original multivalued attribute’s components. The new entity allows the designer to define different values for the attribute. Doing it this way, allows u...
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This document was uploaded on 03/07/2014.
- Spring '09