Sub-class: A distinct sub-grouping of occurrences of an entity type that require being represented in a data model.Įach member of a subclass is also a member of the superclass, i.e., the entity in the subclass is the same entity in the superclass, but has a different role. Super-class: An entity type that includes one or more dissimilar sub-groupings of its occurrences that are required to be represented in a data model. In the below-mentioned figure, whale, shark, and dolphin are generalized as fish, i.e., they have been categorized as the fish. The extended Entity Relationship (ER) models are three types as given below. Enhanced ER models are high level models that represent the requirements and complexities of complex databases. In generalization, some entities are accommodated together into one generalized entity or category based on their similar characteristics. Extended ER is a high-level data model that incorporates the extensions to the original ER model. The relationship between a superclass and a subclass is one-to-one (1:1) and is termed as a super-class/sub-class relationship. 
A generalization is a bottom-up approach. Each member of a subclass is also a member of the superclass, i.e., the entity in the subclass is the same entity in the superclass, but has a different role. Going up in this structure is called generalization, where entities are associated together to represent a more generalized view. As the hierarchy goes up, it generalizes the view of entities, and as you go deep in the hierarchy, it will provide the detail of every entity included. The ER Model has the capability of articulating database entities in a conceptual hierarchical manner. Database managers begin this section by defining what superclasses and subclasses are and by examining superclass/subclass relationships.
The concept of generalization (specialization) is associated with special types of entities known as superclasses and subclasses, and the process of attribute inheritance. # What is Aggregation? What is Generalization / Specialization?
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