Difference Between Generalization and Specialization in Tabular Form
Contents
Comparison Between Generalization and Specialization
The key difference between Generalization and Specialization in DBMS is that a Generalization is a Bottom-up approach. while Specialization is a Top-down approach. Generalization is a bottom-up design process that combines a number of entity sets that have the same features into a higher-level entity. Specialization top-down design process that creates subclasses base on some different characteristics of the entities in the superclass.
Comparison Chart
| Generalization | Specialization |
|---|---|
| It will work in the Bottom-up approach | It will work in a Top-down approach |
| The process of creating groupings from various entity sets are called generalization. |
The process of creating sub-groupings within an an entity set is called specialization |
| Generalization is a process of taking the union of two or more lower-level entity sets to produce a higher-level entity set. |
Specialization is a process of taking a subset of a higher-level entity set to form a lower-level entity set. |
| Generalization starts with the number of entity sets and creates high-level entity set using some common features. |
Specialization starts from a single entity set; it creates different low-level entity set using some different features. |
| Generalization reduces the size of a schema. | Specialization increases the size of a schema. |
| Generalization is applied to a group of entities. | Specialization is applied to a single entity. |
Generalization
- A bottom-up design process that combines a number of entity sets that have the same features into a higher-level entity set.
- The design process proceeds in a bottom-up manner, in which multiple entity sets are synthesized into a higher-level entity set on the basis of common features.
- The database designer may have to first identify a customer entity set with the attributes name, street, city, and customer-id, and an employee entity set with the attributes name, street, city, employee-id, and salary.
- But customer entity set and the employee entity set have some attributes common. This commonality can be expressed by generalization, which is a containment relationship that exists between a higher-level entity set and one or more lower-level entity sets.
- In our example, a person is the higher-level entity set and customer and employee are lower-level entity sets.
- A higher-level entity set is called a superclass and lower-level entity set is called a subclass. So the person entity set is the superclass of two subclasses customer and employee.
- Differences in the two approaches may be characterized by their starting point and overall goal.
Specialization
- A top-down design process that creates subclasses based on some different characteristics of the entities in the superclass.
- An entity set may include sub-groupings of entities that are distinct in some way from other entities in the set.
- For example, a subset of entities within an entity set may have attributes that are not shared by all the entities in the entity set.
- Consider an entity set person, with attributes name, street, and city.
- A person may be further classified as one of the following:
- customer
- Employee
- For example, customer entities may be described further by the attribute customer-id, credit-rating, and employee entities may be described further by the attributes employee-id and salary.
- The process of designating sub-groupings within an entity set is called specialization. The specialization of person allows us to distinguish among persons according to whether they are employees or customers.
- Now again, employees may be further classified as one of the following:
- officer
- teller
- secretary
- Each of these employee types is described by a set of attributes that includes all the attributes of entity set employee plus additional attributes.
- For example, officer entities may be described further by the attribute office-number, teller entities by the attributes station-number and hours-per-week, and secretary entities by the attribute hours-per-week.
- In terms of an E-R diagram, specialization is depicted by a triangle component labeled ISA.
- The label ISA stands for “is a” and represents, for example, that a customer “is a” person.
- The ISA relationship may also be referred to as a superclass-subclass relationship.