Database Management System
Entity Relationship Model
Transaction And Concurrency Control
Files and Storage
What is a Database?
Database is a collection of interrelated data. These databases can be stored in the form of tables. A database can be of any size and varying complexity. A database may be generated and manipulated manually or it may be computerized.
What is the purpose of Database?
In order to overcome the limitation of a file system, a new approach was required. Hence a database approach emerged. A database is a persistent collection of logically related data. Database can easily manage and update data. A database is compact, fast and accurate and much better than file syatem.
What are the drawbacks of using file system for storig data?
Drawbacks of file systems are are:
1) Data redundancy and inconsistency:
The same information may be written in several files. This redundancy leads to
higher storage and access cost. It may lead to inconsistency.
2) Difficulty in accessing data :
The conventional file processing system do not allow data to retrieved in a
convenient and efficient manner according to user choice.
3) Data isolation :
Because data are scattered in various file and files may be in different formats
with new application programs to retrieve the appropriate data is difficult.
4) Integrity Problems:
Developers enforce data validation in the system by adding appropriate code in
the various application program. How ever when new constraints are added, it is
difficult to change the programs to enforce them.
It is difficult to ensure atomicity in a file processing system when transaction
failure occurs due to power failure, networking problems etc.
6) Concurrent access:
In the file processing system it is not possible to access a same file for
transaction at same time
7) Security problems:
There is no security provided in file processing system to secure the data from
unauthorized user access.
What are the difference bteween typical file system and database management system?
1. In file system searching retriving and accessing of data is difficult.
In DBMS these operations are user friendly.
2. In file system there is no standard format of data
In DBMS due to centralized system format of same type of data remain same.
3. In file system there is no or very less security.
In DBMS there is very high level of security,
4. File system has more data redundency.
DBMS has very low or no data redundency.
5. In file system data is isolated.
In DBMS data can be shared.
6. There is chances of inconsistency in file system.
DBMS is consistent.
What are the pros and cons of using Database management system?
Reduction of redundancies:
avoids unnecessary duplication of data and effectively reduces the total amount of data storage required avoiding duplication in the elimination of the inconsistencies that tend to be present in redundant data files.
Sharing of data:
A database allows the sharing of data under its control by any number of application programs or users.
Data integrity means that the data contained in the database is both accurate and consistent.
The DBA who has the ultimate responsibility for the data in the dbms can ensure that proper access procedures are followed including proper authentication schemas for access to the DBS and additional check before permitting access to sensitive data.
DBA resolve the conflict on requirements of various user and applications. The DBA chooses the best file structure and access method to get optional performance for the application.
1. DBMS software and hardware (networking installation) cost is high
2. The processing overhead by the dbms for implementation of security, integrity and sharing of the data.
3. centralized database control
4. Setup of the database system requires more knowledge, money, skills, and time.
5. The complexity of the database may result in poor performance.
Explain various levels of abstaction present in DBMS.
1. External level abstraction:
The external level is at the highest level of database abstraction . At this level, there will be many views define for different users requirement.
2. Conceptual level:
The conceptual schema hides the details of physical storage structures and concentrate on
describing entities , data types, relationships, user operations and constraints.
3. Internal level:
This is a lowest level, which describes how the data is actually stores and describes the data structures and access methods to be used by the database .
Image: 3 levels of abstraction
Diffrentiate between Physical Schema and logical schema.
Physical Schema: It shows actual storage of data and its storage forms like memory/disc. It is the implementation of the data structure.
Logical schema: It is more like definition of the data structure. It defines tables ,views and integrity constraints.
What do you understand by physical data independence?
Physical data independence is the ability to modify the physical scheme without making it necessary to rewrite application programs.
Such modifications include changing from unblocked to blocked record storage, or from sequential to random access files.
What is an instance in DBMS?
The data or instance stored at particular moment in DBMS is called instance. Instance can change frequently.
Define Database Management System.
It is a collection of programs that enables user to create and maintain a database. In other words it is
general-purpose software that provides the users with the processes of defining, constructing and manipulating the database for various applications.