Tuesday, 12 October 2021

Entity Clustering in EER Modeling

An entity clustering is a virtual entity type used to represent multiple entities and relationships in the ER diagrams. an entity clustering is formed by combining multiple interrelated entities into a single entity object.

Entity clustering is useful way to represent a data model for a large and complex organizations.

Example:

To understand entity cluster, consider the example of Hospital Management. In hospital, the DOCTORS treat the PATIENT. The DOCTORS are paid by the MANAGEMENT which builds buildings. The DOCTORS can be either general physician or specialist like those with MS or MD. The patient can be either inpatient or outpatient. It is to be noted that only outpatient will be allotted bed. If we have to represent the earlier ideas, it can be done using EER diagram as


The EER diagram is found to be complex; the same idea is represented using Entity Clusters as


Here the DOCTOR specialization is clustered into DOCTORS entity and the PATIENT specialization is clustered into simply PATIENT. At the first glance, it may look like reduction of EER model to ER model, but it is not so. Here the entities as well as relationships are clustered into simply entity set.

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