data base

1. Database Schema
A database schema is the skeleton structure that represents the logical view of the entire database.
It defines how the data is organized and how the relations among them are associated. It
formulates all the constraints that are to be applied on the data.
A database schema defines its entities and the relationship among them. It contains a descriptive
detail of the database, which can be depicted by means of schema diagrams. It’s the database
designers who design the schema to help programmers understand the database and make it
useful.
Data Independence
capacity of changing the Schema at one level without affecting the other
A database schema can be divided broadly into two categories −
Physical Database Schema − This schema pertains to the actual storage of data and its
form of storage like files, indices, etc. It defines how the data will be stored in a secondary
storage.
Logical Database Schema − This schema defines all the logical constraints that need to
be applied on the data stored. It defines tables, views, and integrity constraints.

2. DBMS architecture
What is 3 level architecture ?
This architecture has three levels:
1. External level
2. Conceptual level
3. Internal level
1. .External level
2. It is also known as view level.
3. This is highest level architecture and closest to the user.
4. The user doesn’t need to know the database schema details such as
data structure, table definition etc.
5. External level is related to the data which is viewed by individual end
users.

3. 2. Conceptual level
1. It is also known as logical level.
2. The conceptual level is a higher level than the physical level.
3. This level is maintained by DBA(database administrator).
4. The whole design of the database such as relationship among
data ,schema of data etc.are described in this level.
5. It is the middle level between external or internal levels.
3. Internal level
1. It is also known as physical level.
2. This is the lowest level of the architecture.
3. This data is stored in the external hard drives in the form of bits.
4. This level describes how the data actually stored in the storage
device.
5. This physical level also discuess encryption techniques.
6. This level is also responsible for allocating space of the data.