System Analysis and Design
System Design
- Mr. Ahmad Al-Ghoul
learning Objective
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Explain the importance of codes
and describe various coding
schemes
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Using Codes During System Design
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Overview of Codes
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A code is a set of letters or numbers that represents a
data item. Codes can be used to simplify output,
input, and data formats.
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Because codes often are used to represent data, you
encounter them constantly in your everyday life
They save storage space and costs, reduce transmission
time, and decrease data entry time
Can reduce data input errors in situations when the coded
data is easier to remember and enter than the original
source data
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Using Codes During System Design
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Code example
 A ZIP code contains multiple items of information compressed
into nine digits
 First digit identifies one of ten geographical areas of the USA
 The next three digits identifies a major city or major distribution
point
 Fifth digit identifies an individual post office, an area within a city
 The last four digits identify a post office box or a specific street
address
Broad geographical
area in eastern U.S
Local postal
delivery point
Elizabeth City, NC
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Specific location for College of
the Albemarle
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Using Codes During System Design
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Types of Codes
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Companies use many different coding
methods
Codes should be easy to learn and apply
When the analyst crate codes for the
information system, he first should obtain
comments and feedback from users
We will describes seven common coding
methods
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Using Codes During System Design
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Types of Codes
1.
2.
3.
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Sequence codes: Sequence codes are numbers or
letters assigned in a specific order. Sequence codes
contain no additional information other than an
indication of order of entry into a system.
Block sequence codes: use blocks of numbers for
different classification
Alphabetic codes: use alphabet letters to distinguish
one item from another based on a category, an
abbreviation, or an easy-to-remember value, called
a mnemonic code. Many classification codes fit
more than one of the following definitions:
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Using Codes During System Design
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Types of Codes
a.
b.
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Category codes: identify a group of related items. For
example, a local department store may use a twocharacter category code to identify the department in
which a product is sold.
Abbreviation codes: Abbreviation codes are alphabetic
abbreviations. For example, standard state codes include
NY for New York, ME for Maine, and MN for Minnesota. –
mnemonic codes: use a specific combination of letters that
are easy to remember. Many three-character airport codes
are mnemonic codes. For example, LAX represents Los
Angeles International Airport
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Using Codes During System Design
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Types of codes
4.
Significant digit codes: Significant digit codes
distinguish items by using a series of subgroups of
digits. ZIP codes, for example, are significant digit
codes.
Warehouse location code
Section code
Floor number
Bin number
Aisle number
Sample of a code that uses significant digits to pinpoint the location of an inventory item.
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Using Codes During System Design
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Types of codes
5.
Derivation codes: Derivation codes combine
data from different item attributes, or
characteristics, to build the code. Most
magazine subscription codes are derivation
codes.
A magazine subscriber code is derived from various parts of the name and
address.
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Using Codes During System Design
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Types of codes
6.
7.
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Cipher codes: Cipher codes use a keyword to
encode a number. A retail store, for example, may
use a 10-letter word, such as CAMPGROUND, to
code wholesale prices, where the letter C
represents 1, A represents 2, and so on.
Action codes: Action codes indicate what action is to
be taken with an associated item. For example, a
student records program might prompt a user to
enter or click an action code such as D (to display
the student's record), A (to add a record), and X (to
exit the program).
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Using Codes During System Design
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Developing a Code
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Codes should be easy to remember, decipher, and
verify
Keep the following suggestions in mind when
developing a code:
1.
2.
3.
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Keep codes concise. Do not create codes that are longer
than necessary
Allow for expansion. A coding scheme must allow for
reasonable growth in the number of assigned codes
Keep codes stable. Changes in codes can cause consistency
problems and require data updates. During the changeover
period, you have to change all the stored occurrence of a
particular code and all documents containing the old code,
as users switch to the new code
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Using Codes During System Design
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Developing a Code
4.
5.
6.
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Make codes unique. Codes used for identification
purposes must be unique to have meaning
Use sortable codes. ensures that data sorts into
usable groups.
Avoid confusing codes. Avoid allowing both
letters and numbers to occupy the same
positions within code because some of those are
easily confused, like the number 0 and the letter
O
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Using Codes During System Design
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Developing a Code
7.
8.
9.
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Make codes meaningful. Codes must be easy to
remember, useful for users, convenient to use, and
easy to encode and interpret. Using ENG as the code
for the English department is easier to interpret and
remember than either XVA or 132
Use a code for a single purpose. Do not use a single
code to classify two or more unrelated attributes.
Keep codes consistent. For example, if the payroll
system already is using two digit codes for
departments, do not create a new, different coding
scheme for the personal system
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Sequence Summary
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You learned that a code is a set of letters or
numbers used to represent data in a system
By using codes, you can speed up data entry,
reduce data storage space, and reduce
transmission time
Codes also can be used to reveal or to conceal
information
The main types of codes are sequence codes,
block sequence codes, classification codes,
alphabetic codes (including category codes,
abbreviation codes, and mnemonic codes),
significant digit codes, derivation codes, cipher
codes, and action codes
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Sequence Summary
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In this Sequence we have
 Defined the term code
 Explained the the importance of codes
 described various coding schemes including
sequence codes, block sequence codes,
classification codes, alphabetic codes
(including category codes, abbreviation codes,
and mnemonic codes), significant digit codes,
derivation codes, cipher codes, and action
codes
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Reference
[1] System Analysis and Design, Sixth
Edition
Authors: Gary B. Shelly, Thomas J.
Cashman and Harry J. Rosenblatt
Publisher: SHELLY CASHMAN SEWIES.
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