Various Views Of Data
It refers that how database is actually stored in database, what data and structure of data used by database for data. So describe all this database provides user with views and these are- Data abstraction
- Instances and schemas.
Data abstraction
As a data in database are stored with very complex data structure so when user come and want to access any data, he will not be able to acess data if he has go through this data structure. So to simplify the interaction of user and database, dBMS hides some informations which is not of user interest, a this is called data abstraction:- So developer hides complexity from user and store abstract view of data.
Data abstraction has three level of abstractions
- level / internal level
- Logical level / conceptual level
- view level / external level
Physical level:- this is the lowest level of data abstraction which describe How data is actual stored in database. This level basically describe the data structure and access path /indexing use for accessing file.
Logical level:- The next level of abstraction describe what data are stored in the database and what are the relationship existed among those of data.
View level:- In this level user only interact with database and the complexity remain unview . user see data and there may be many views of one data like chart and graph.
- Let suppose we have customer information so at physical level this record[ customer information] can be described as block of storage.
- At the logical level these record can be described as fields and attributes along with their data type and relationship among each other.
- At view level user just interact with system with the help of GUI and enter the detail at the screen. User not aware of what and how data is stored.
