Advantages of Database Approach
Centralized control - Data access and management can be controlled centrally.
Reduction of redundancy - Duplication of data is highly reduced through constraints and better structure of database.
Sharing of data - It is made possible to share same data to different users through application programs.
Security - Confidential messages can be stored with only authorized persons given access to.
Data Integrity - Data can be checked for its integrity such as limit, data type.
Drawbacks of Database Approach
It is costly - Software and hardware specifically for database management is required.
Centralization problem - Adequate backup is required incase of failure.
Complexity of backup and recovery - Recovering a crashed database is a technical process requiring trained professionals.
Three Levels of Database Architecture
These are three distinct levels at which data items can be described.
- External
- Conceptual
- Internal
Objectives of the 3 Level Architecture
Each user should be able to access the same data but have a different customized view of data.
The database should be able to change the conceptual structure of database without affecting all users.
Users should not have to deal directly with the physical database details.
The database should be able to change database storage structures without affecting the user's views.
The internal structure of the database should not be affected by changes to the physical storage.
External or View Level
It is the user's view of the database.
Each user has a view of the real world represented in a form that is familiar for that user.
Conceptual Level
Describes what data is stored in the database, how it is stored, and relationship among the data.
It contains the following:
All entities, their attributes, and relationships.
Constraints on the data.
Semantic information about the data.
Security and Integrity information.
Internal or Physical Level
It deals with the physical representation of the database in the computer.
Deals with the data structures and file organizations used to store data on the storage devices.
It mainly contains:
Storage space allocation for data and indexes.
Record descriptions for storages(with stored sizes for data items).
Data compression and encryption technics.
