Object-Based Logical Model

Object- Based Logical Model

There are various object-based logical models, such as
Entity-Relationship (ER) model, object- oriented model, and binary model. The most widely used is the ER model. It is accepted as an ideal data model for the database design. Peter Chen introduced this model in 1976, and since then several people have added value to it.

The ER Model

 The ER model views the real world as a collection of objects or entities and the relationship among them. Chen introduced not only the ER model, but also a corresponding diagramming technique.

Entities 

Chen defined an entity as “a thing, which can be easily identified”. An entity is any object, place, person, or activity about which data is recorded. An entity can be categorized as entity type and entity instance. An entity type is a set of things that share common properties.

Relationships

 Chen defined a relationship as “an association among entities”. For example, there is a relationship between students and teachers. This relationship represents the fact that a teacher teaches several students and a student is taught by several teachers. This relationship could be named TEACH.