Extended Entity-Relationship Model Edit
The Extended Entity-Relationship Model is a more complex and high-level model that extends an E-R diagram to include more types of abstraction, and to more clearly express constraints. All of the concepts contained within an E-R diagram are included in the EE-R model, along with additional concepts that cover more semantic information. These additional concepts include generalization/specialization, union, inheritance, and subclass/superclass.
Generalization and SpecializationEdit
You can think of generalization as developing a diagram from the bottom up, whereas you can think of specialization as taking a top down approach to development. These two processes are used to incorporate more meaning into EER models.
Specialization is a process of defining two or more sub-types of a super-type forming super-type,sub-type relationship by using generic entity is known as SPECIALIZATION.It is a complete reverse process of Generalization technique.i.e., Specialization follows a Top down approach.In Specialization is sub-type is formed based on some different characteristics such as attributes or relationships.
Generalization is a process of defining generic entity from set of specialized entities i.e., by using subset entities we are developing a generic entity. This process or technique is called generalization.It follows Bottom-Up approach. For example, The entities CAR and TRUCK have similar properties and attributes, so they could be generalized into a superclass of AUTOMOBILE.
A union (also known as a category) is a collection of superclasses that acts as a union between objects of different entity types. Instances of the subclass will inherit the attributes of only one of the superclasses, depending on the union that it belongs to.