One fundamental characteristic of the database approach is that it provide some level of data abstraction by hiding details of data storage that are not needed by most database users. A data models: is a collection of concept that can be used to describe the structure of a database, by structure of a database, we mean the data types, relationships and constraints that should hold for the data. Most data models also include a set of basic operations for specifying retrievals and updates on the database.
CATEGORIES OF DATA MODELS :-Many data models has been proposed which we can categories according to the types of concepts they use to describe the database structure. Conceptual data models provide concepts that are close to the way many users perceive data, whereas low level or physical data models provide concepts that describe the detail of how data is stored in the computer conceptual data models use concepts such as entities, attributes and relationships, representational or implementation data models are the models used most frequently in traditional commercial DBMS. An entity represents a real world object or concepts, such as employee or a project. An attribute represents some property of interest that further describes an entity, such as employee’s name or salary. A relationship among two or more entities represents an association among two or more entities. Data base changes over time when information is inserted or deleted. The collection of information stored in the database at a particular moment is called on instance of the database. The overall design of the database is called the database schema.
A schema diagram in example display only name of records types (entities) and names of data items(attributes) and does not show the relationships among the various files.
The schema will remain the same while the values filled into it change from instant to instant. When the schema framework is filled in with data items values, it is referred as an instance of the schema. The data in the database at a particular moment of time is called a database state. “The description of a database is called database schema.”
