Database and Database Management System

Database And Database Management System In Brief

A computer system organizes data in a hierarchy that begins with bits, and proceeds to bytes, fields, records, files and databases. Bit is the smallest unit of data that a computer can process. It's valid values are 0s and 1s. Similarly Byte is a group of 8 bits.

 Fields are the  logical grouping of characters into a word, a small group of words, or a complete number is called Field. Records are the logical grouping of related fields whereas Files are the grouping of related records.


A database is a collection of information that is organized so that it can easily be accessed, managed, and updated.

Advantages of Database:
A. Database reduce  the problem of Data Redundancy.
B. It help in avoiding the  Inconsistency.
C. Data sharing
D. Standards can be enforced.
E.Security restrictions can be applied.
F. Integrity or Accuracy can be maintained.

Characteristics of Database:
A. It Should be able to store all kinds of data that exists in this real world.
B. It Should be able to relate the entities / tables in the database by means of a relation.
C. Data and application should be isolated. Because database is a system which gives the platform to store the data, and the data is the one which allows the database to work. Hence there should be clear differentiation between them.
D. No Data Redundancy :There should not be any duplication of data in the database. Data should be stored in such a way that it should not be repeated in multiple tables
E. DBMS has a strong query language. Once the database is designed, this helps the user to retrieve and manipulate the data.
F. Database must be ’Shared’ i.e Multiple users should be able to access the same database, without affecting the other user.
G. Database should also provide security, i.e.; when there are multiple users are accessing the database, each user will have their own levels of rights to see the database.
H. Database should also support ACID property. i.e.; while performing any transactions like insert, update and delete, database makes sure that the real purpose of the data is not lost.

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Storing and Accessing Records:

Indexed Sequential Access Method (ISAM):
 Indexed Sequential Access Method (ISAM) uses an index of key fields to locate individual records. An index to a file lists the key field of each record and where that record is physically located in storage. Records are stored on disks in their key sequence. A track-index shows the highest value of the key field that can be found on a specific track. To locate a specific record, the track index is searched to locate the cylinder and the track containing the record. The track is then sequentially read to find the record

• Direct File Access Method:

 Direct File Access Method uses the key field to locate the physical address of a record. It is most appropriate when individual records must be located directly and rapidly for immediate processing.

DBMS vs Traditional File Approach 

• .DBMS is the Database Management System. A database management system coordinates both the physical and the logical access to the data, whereas a file-processing system coordinates only the physical access.
• A database management system is designed to allow flexible access to data (i.e. queries), whereas a file-processing system is designed to allow predetermined access to data (i.e. compiled programs).
• A database management system is designed to coordinate multiple users accessing the same data at the same time. A file-processing system is usually designed to allow one or more programs to access different data files at the same time. In a file-processing system, a file can be accessed by two programs concurrently only if both programs have read-only access to the file.
• Redundancy is control in DBMS, but not in file system.
• Unauthorized access is restricted in DBMS but not in the file system.
• DBMS provide back up and recovery whereas data lost in file system can’t be recovered.
• DBMS provide multiple user interfaces. Data is isolated in file system.

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Advantages of DBMS:

A. Data Mapping and Access: 
- DBMS defines the way to map any two related tables by means of primary key foreign key relationship.
B. Data Redundancy: By the introduction of primary key in the table, data redundancy problem is reduced to great extent. As we saw, primary key is the unique column for each record, when there is a re-entry of same record, it does not allow saving such records. DBMS has strong designing techniques like normalization which makes sure the same copy of data is not stored in same table or in multiple tables. It makes sure all the information are stored only once in the database tables.
C. Data Independence and Consistency: - DBMS defines a standard to represent the data in the form of rows and columns. It also stores the information about the tables, columns, keys, storage space, used space, available space etc separately from the logical data. Hence they totally independent of the way they are stored and the data being stored. Any changes to the physical storage (like disks, tapes etc) or structure, does not harm the data being stored. Since DBMS defines each columns and rows at the beginning itself and controls the way data being entered, there is no affect on the programs or any other tables or data. Hence the consistency of the data also maintained.
D. Security: - DBMS allows different levels of access to different users based on their roles, it prevents data overwriting and deletion by unauthorized users.

E. Integrity: - DBMS allows having restrictions on individual columns. It would be defined while designing the table itself, which means chances of entering wrong values in a table is greatly reduced. F. Atomicity: - DBMS makes sure either the transaction is fully complete or it is rolled back to the previous committed state. It does not allow the system to be in a partially committed state.
G. Concurrent Access: - DBMS provide access to multiple users to access the database at the same time. It has its own mechanism to have concurrency accesses and hence avoid any incorrect data in the system.

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