How do represent an multi-valued attribute in E-R diagram? How can we transfer or any attribute into our relational design?
Multi-valued attribute can be represented by double dotted ovals in an ER Diagram.
Following are the rules to follow for transformation of multi-valued attribute into relational model:
- An Entity type with a multivalued attribute is transformed into two relations
- One relation contains the entity type and other simple attributes whereas the second relation has the multivalued attribute. In this way only single atomic value is stored against every attribute.
- The primary key of the second relation is also the primary key of the second relation. So, in the second relation the primary key is the combination of two attributes.
- All values are accessed through reference of the primary key that also serves as foreign key.
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