When a multivalued attribute is encountered, the designer has two alternatives which can be followed.
- The multivalued components can be split into its components and kept in the same entity. But the only condition with the usage of this approach is that only single entries are stored at each level. For example, CUSTOMER_TELEPHONE can be decomposed into CUST_HOMEPHN, CUST_MOBILE AND CUST_FAX_NUMBER. If the customer has more than one mobile number, then this structure will not be able to store more than a single value. Hence for each component, only a single value will be stored.
- The second approach involves the creation of a new entity which would comprise of the components of the multivalued components. This new entity can be linked to the entity in which the multivalued attributes were originally present. This method is most favorable and desirable when the total number of results in the multivalued attributes is unlimited. This holds significance for practical purposes also. The most appropriate example of this approach is the classification employees as “technical” which enables them to possess certifications in various areas as well as levels.
Senior Consultant at SwiftRadius