uniquely identifies a particular tuple (row in a relation (table)). Name Age Name Teacher Malar C++ Kannan Suncar Php Ramakrishnan Velu Python Vidhya Marks Relational Model Fig. . .
Network Model Network database model is an extended form of hierarchical data model. The difference between hierarchical and Network data model is : • In hierarchical model, a child record has only one parent node, 12th Computer Chapter - - Database Concepts • In a Network model, a child may have many parent nodes. It represents the data in many- to-many relationships. • This model is easier and faster to access the data.
Network Model Fig. . School Office Staff Room Library Student Student has parent node This child has one parent node School represents the parent node Library, Office and Staff room is a child to school Student is a child to library, office and staff room (one to many relationship) . Entity Relationship Model.
(ER model) In this database model, relationship are created by dividing the object into entity and its characteristics into attributes. It was developed by Chen in . This model is useful in developing a conceptual design for the database. It is very simple and easy to design logical view of data.
The developer can easily understand the system by looking at ER model constructed. Rectangle represents the entities. E.g. Doctor and Patient Ellipse represents the attributes E.g.
D-id, D-name, P-id, P-name. Attributes describes the characteristics and each entity becomes a major part of the data stored in the database. Diamond represents the relationship in ER diagrams E.g. Doctor diagnosis the Patient 12th Computer Chapter - - ER model Fig.