Underlying the structure of a database is the data model. Data Model means to model the data. That is to give a shape to the data or to give figure to the data. A data model makes it easier to understand the meaning of the data by its figure.
A collection of high – level data description that hide many low – level storage details. A data model can also be defined as a collection of conceptual tools for describing data, data relationships, data semantics and consistency constraints. So the DBMS allows a user to define the stored data in terms of data model.
E R Model:
The entity-relationship (E-R) data model is based on a perception of a real world that consists of a collection of basic objects, called entities, and of relationships among these objects.
Entity: A real world object
E.g. customers, accounts, bank branch
Relationship: An association between entities
E.g. Pursues, works-for, managers
Attribute: Property of the Entity.
E.g. empno, ename, sal
Widely used for database design:
Database design in E-R model usually converted to design in the relational model, which is used for storage, and processing.
The overall logical structure (schema) of a database can be expressed graphically by an E-R diagram, which is built up from the following components:
Rectangles, which represent entity sets.
Ellipses, which represent attributes.
Diamonds, which represent relationships among entity sets.
Lines, which link attributes to entity sets and entity sets to relationships Each component is labeled with the entity or relationship that it represents.