A Database model described the logical design of data. The model describes the relationships between different parts of the data.
There are three models have been in use.
- Hierarchical Model
- Network Model
- Relational Model
This Modal is Based on parent child Concept.In this model each entity has only one parent but can have several children . At the top of hierarchy there is only one entity which is called Root.
In the network model, entities are organised in a graph,in which some entities can be accessed through several path
In this model, data is organised in two-dimesional tables called relations. The tables or relation are related to each other.
Logical View of database are Called as Schema. It tells about how the data is organized and how relation among them is associated. It formulates all database constraints that would be put on data in relations, which resides in database.
a Database Schema are as-
- A database schema defines its entities and the relationship among them.
- Database schema is a descriptive detail of the database, which can be depicted by means of schema diagrams.
- All these activities are done by database designer to help programmers in order to give some ease of understanding all aspect of database.
Database schema can be divided broadly in two categories:
Physical Database Schema: This schema constraints to the actual storage of data and its form of storage like files, directory etc. It defines the how data will be stored in secondary storage etc.
Logical Database Schema: This defines all logical constraints that need to be applied on data stored. It defines tables, views and integrity constraints etc.