Ppt of dbms e r features
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This document discusses entity-relationship (E-R) modeling concepts including specialization, generalization, aggregation, and redundant relationships. It provides definitions and examples of each concept. Specialization defines subclasses based on distinguishing attributes. Generalization defines a superclass from common attributes of subclasses. Aggregation treats relationships as higher-level entities. An E-R diagram example shows representing aggregation. Another example shows a diagram with redundant relationships.
Ppt of dbms e r features
- 1. GANDHINAGAR INSTITUTE OF TECHNOLGY Department of Information Technology E-R Features Group ID: IT_A1_10 Students Names: Akabari Nirali (130120116002) Akanksha Sharma (130120116003) Guided By: Prof. Anirudhdha Nayak Database Management System(2130703)
- 2. Presentation outlines: E-R concept Specialization Generalization Aggregation E-R diagram notation for representing specialization E-R diagram with redundant relationship E-R diagram with Aggregation
- 3. Basic E-R concepts The original concept of the entity- relationship model was given by Chen in 1976. High level conceptual(logical) data model. Widely used in database design to represent a conceptual schema. A conceptual schema represented by the E-R model is called an E-R schema.
- 4. The basic notation used in E-R diagram are illustrated below: An entity set An Attribute A Relationship set Link between an entity set & attribute
- 5. Specialization Specialization is the process of defining sub-class based on some distinguishing characteristics. In other words, specialization identifies the sub-sets possesses some attributes Specialization is a top-down process to define super-class/sub-class relationships.
- 7. Generalization Generalization is the process of defining a super-class from sub- classes based on some common characteristics. In other words, generalization identifies a super-class from different entity-sets(or sub-classes). Generalization is a bottom-up process to define super-class/sub-class relation.
- 8. A bottom-up design process – combine a number of entity sets that share the same features into a higher-level entity set. Specialization and generalization are simple inversions of each other; they are represented in an E-R diagram in the same way. The terms specialization and generalization are used interchangeably.
- 10. Aggregation Aggregation is an abstraction through which relationships are treated as higher level entities. Thus, for our example, we regard the relationship set works on as a higher- level entity set called works on. Such an entity set is treated in the same manner as is any other entity set. Figure shows a notation for aggregation commonly used to represent this situation.
- 12. E-R Diagram With Redundant Relationships