Unit-I

2011-10-05T03:36:00.000-07:00

1. What is Data?
Data is a collection of raw information.

2. What is Information?
Information is a collection of processed data

3. What is Database?

Database is a collection of inter-related data items that can be processed by one or more
application systems.

4. What is DBMS?

Database Management System is a collection of interrelated data and set of programs to
access those data. The DBMS is a general purpose software system that facilitates the
process of defining constructing and manipulating databases for various applications.

5. What are the disadvantages of File Oriented System?
The typical file-oriented system is supported by a conventional operating system.
Permanent records are stored in various files and a number of different application programs
are written to extract records from and add records to the appropriate files.
The following are the disadvantages of File-Oriented System:
(i). Data redundancy and Inconsistency: Since files and application programs are created
by different programmers over a long period of time, the files are likely to be have different
formats and the programs may be written in several programming languages. Moreover, the
same piece of information may be duplicated in several places. This redundancy leads to higher
storage and access cost. In addition, it may lead to data inconsistency, i.e. the various copies of
same data may no longer agree.
(ii). Difficulty in accessing data: the conventional file processing environments do not allow
needed data to be retrieved in a convenient and efficient manner. Better data retrieval system
must be developed for general use.
(iii). Data isolation: Since data is scattered in various files, and files may be in different
formats, it is difficult to write new application programs to retrieve the appropriate data.
(iv). Concurrent access anomalies: In order to improve the overall performance of the
system and obtain a faster response time, many systems allow multiple users to update the
data simultaneously. In such an environment, interaction of concurrent updates may result in
inconsistent data.
(v). security problems: Not every user of the database system should be able to access all
the data. For example, in banking system, payroll personnel need only that part of the database
that has information about various bank employees. They do not need access to information
about customer accounts. It is difficult to enforce such security constraints.
(vi). Integrity problems: The data values stored in the database must satisfy certain types of
consistency constraints. For example, the balance of a bank account may never fall below a
prescribed amount. These constraints are enforced in the system by adding appropriate code in
the various application programs. When new constraints are added, it is difficult to change the
programs to enforce them. The problem is compounded when constraints involve several data
items for different files.
(vii). Atomicity problem: A computer system like any other mechanical or electrical device is
subject to failure. In many applications, it is crucial to ensure that once a failure has occurred
and has been detected, the data are restored to the consistent state existed prior to the failure.

6. What are the advantages of DBMS over File Oriented System?

The following are the advantages of DBMS:

I. Data Redundancy: A major difficulty was that many applications used their own special files of data. Thus, some data items were common to several applications. In a bank, for example, the same customer name might appear in a checking account file, a savings account file and an installment loan file. Moreover, even though it was always the customer name, the related field often had a different name in the various account files. Thus, CNAME in the checking account file became SNAME in the savings account file and INAME in the installment loan file. The same field also has a different length in the various files. For example, CNAME could be up to 20 characters, but SNAME and INAME might be limited to 15 characters. This redundancy increased the overhead costs of maintenance and storage. Data redundancy also increased the risk of inconsistency among the various versions of common data.

Suppose a customer’s name was changed. The name field might be immediately updated in the checking account file, updated next week in the savings account file and updated incorrectly in the installment loan file. Over time, such discrepancies can cause serious degradation in the quality of information contained in the data files.

Database systems can eliminate data redundancy, since all applications share a common pool of data. Essential information such as customer name will appear just once in the database.

BCOM RDBMS

Unit-I