Relational Model¶
All data is stored in tables
Example¶
| ID | name | department | salary |
|---|---|---|---|
| 100 | John | Physics | 100000 |
| 125 | Doe | Chemistry | 98000 |
| 235 | Dane | Biology | 90000 |
| 175 | Joe | Mathematics | 100001 |
Layers of Abstraction¶
Application Level¶
- This level is beyond the scope of management of the DBMS, but relies on it
- The application converts data from the DBMS into a human-readable format, which conceals everything irrelevant to the user
View Level¶
- A view is modified, regulated, and pre-digested access to a certain section of the database
- A view can perform data hiding for security purposes, and also hide details of datatypes
Logical Level¶
- This level describes the nature of the data shown in the database
- It also regulates the relationships between the data entities
- Lastly, it tells us about the schema, i.e. the constraints that the data columns are subject to
Physical Level¶
- The physical level decides how data is stored on the disk
- This is, understandably, something that a data analyst doesn't care much about. This decides the efficiency and effectiveness of operations and storage, but doesn't affect the behaviour of the DBMS
Data Independence¶
Data independence is the ability of a lower layer of abstraction to be independent of a higher layer of abstraction. This is a very helpful paradigm, even besides the scope of database management, it is essential to the working of almost any computer program
Logical Data Independence - is the ability to modify the logical schema without needing to rewrite application programs
Physical Data Independence - is the ability to modify the physical schema without having to rewrite the logical schema