Lecture 1: Introduction to Database - Nubacad.com

Past System for Managing Information
The File Systems Approach
• The information is stored in permanent system files.
• A number of application programs are written to
manipulate the files.
General
Ledger
File
Production
Planning
File
Invoicing
File
Despatch
File
Personnel
File
Payroll
File
Inventory
File
Order
Entry
File
Sequential Files
File Organisation
• records are stored in a fixed sequence
• records can only be read in that sequence, starting from
the first record
• records can only be added at the end of the file (append)
• sequential files are not efficient
Indexed Files
• Use an index to access records in a random fashion.
• Records can be sorted according to an attribute or
preference. (e.g Alphabetically, Ascending, Descending,
etc.)
• Indexed files are efficient, and faster to access.
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Disadvantages of File Processing System
• Data Redundancy: Data Redundancy means
same information is duplicated in several files.
• Data Inconsistency: Data Inconsistency means
different copies of the same data are not
matching. That means different versions of same
basic data are existing. This occurs as the result
of update operations that are not updating the
same data stored at different places.
• Example: Address Information of a customer
is recorded differently in different files.
Disadvantages of File Processing System (cont..)
• Difficulty in Accessing Data: It is not easy to
retrieve information using a conventional file
processing system. Convenient and efficient
information retrieval is almost impossible using
conventional file processing system.
• Data Isolation: Data are scattered in various files,
and the files may be in different format, writing new
application program to retrieve data is difficult.
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