Developing a Conceptual Model › Identifying Entities and Attributes › Generalization and Differentiation of Entities

Generalization and Differentiation of Entities

You can refine the information, represented as entities, in your data model as often as needed to meet your data requirements while designing the database for your application. This topic explains how you use the two opposite processes called "generalization" and "differentiation" to refine your identified primary entities.

Generalization and differentiation involve deleting or adding entities to your model. At this early design phase, these processes affect the number of files that will have to be created for your application. Generalization and differentiation mean naming and renaming the entities and attributes, and assigning and reassigning different attributes to different entities.

With generalization, you combine two entities representing different types of the same thing into one entity. With differentiation, you divide one entity into two separate ones because you decide the entity is actually representing two different things, and should be divided.

Going back to the Order Entry example discussed earlier, you may want to review the Purchase Order and Supply Request entities. Do you really need both Purchase Order and Supply Request? Are they both representing the same thing: a customer's request for a product not in stock, which the company will have to purchase from a specific vendor or supplier? If you decide they are, then they can be generalized and combined into one entity:

The Vendor and Supplier can also be generalized and combined into one entity, Vendor, in the same way. To discuss differentiation, use the Order Entry example again and look at the Vendor entity.

Does Vendor represent all of the information about a vendor, or are there special vendors with special information? In this case, a vendor from a foreign country requires special import and duty information that a native vendor does not require. Because of this special information, you need to add a new entity: