Transcript chap4 seq6.ppt

System Analysis and Design
System Design
- Mr. Ahmad Al-Ghoul
Learning Objectives
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Use validation checks for reducing
input errors
Design effective source
documents and input controls
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Input Design
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Input Errors
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Reducing the number of input errors improves
data quality
The best defense against incorrect data is to
identify and correct errors before they enter
the system by using data validation checks
A data validation check improves input quality
by testing the data and rejecting any entry
that fails to meet specified conditions
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Input Design
Input Errors
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You can design at least eight types of data validation
checks into the input process
1. Sequence check: are used when the data must
be in some predetermined sequence. If the user
must enter work orders in numerical sequence, for
example, then an out-of-sequence order number
indicates an error. If the user must enter
transactions chronologically, then a transaction
with an out-of-sequence date indicates an error.
2. Existence check: are used for mandatory data
items. For example, if an employee record requires
a Social Security number, an existence check
would not allow the user to save the record until
he or she enters a suitable value in the SSN field.
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Input Design
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Input Errors
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Data type check: is used to ensure that a data item fits
the required data type. For example, a numeric field must
have only numbers or numeric symbols, and an alphabetic
field can contain only the characters A through Z or the
characters a through z.
Range check – limit check: tests data items to verify that
they fall between a specified minimum and maximum
value. The daily hours worked by an employee, for
example, must fall within the range of 0 to 24.
Reasonableness check: identifies values that are
questionable, but not necessarily wrong. For example,
input payment values of $0.05 and $5,000,000.00 both
pass a simple limit check for a payment value greater than
zero, and yet both values could be errors.
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Input Design
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Input Errors
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Validity check: is used for data items that must
have certain values. For example, if an inventory
system has 20 valid item classes, then any input item
that does not match one of the valid classes will fail
the check.
Combination check: performed on two or more
fields to ensure that they are consistent or reasonable
when considered together. Even though all the fields
involved in a combination check might pass their
individual validation checks, the combination of the
field values might be inconsistent or unreasonable.
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Input Design
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Input Errors
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Batch controls – referential integrity: is used for
data items that must have certain Batch controls: are
totals used to verify batch input. Batch controls
might check data items such as record counts
and numeric field totals. For example, before
entering a batch of orders, a user might calculate
the total number of orders and the sum of all the
order quantities. When the batch of orders is
entered, the order system also calculates the
same two totals. If the system totals do not
match the input totals, then a data entry error
has occurred.
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Input Design
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Source Documents
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A form used to request and collect input data,
trigger or authorize an input action, and
provide a record of the original transaction.
During the input design stage, you develop
source documents that are easy to complete
and inexpensive.
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Input Design
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Source Documents
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Form layout
refers to the physical appearance and placement
of data on a form.
 Form layout makes the form easy to complete and
provides enough space, both vertically and
horizontally, for users to enter the data.
 A form should indicate data entry positions clearly
using blank lines or boxes and descriptive captions
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Input Design
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Source Documents
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Form layout
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Captions may be
one of the
following:
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Line caption,
putting the caption
on the same line,
above the line,
below the line, or
combination
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Input Design
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Source Documents
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Form layout
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Captions may be one of the following:
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Boxed caption, providing a box for data instead of a line
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Input Design
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Source Documents
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Form layout
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Vertical check boxes, lining up choices or alternatives
vertically
Horizontal check boxes, lining up choices or alternatives
horizontally [1]
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Input Design
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Source Documents
The six sections of a form
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Heading zone
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Control zone
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Area of a form contains the codes, identification
information, numbers, and dates that are used for
storing completed forms.
Instruction zone
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Area of a form that usually contains the company
name or logo and the title and form number.
Area of a form contains instructions for completing
a form
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Input Design
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Source Documents
The sex sections of a form
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Body zone
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Totals zone
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If a form has data totals, they will appear in this
section of the form.
Authorization zone
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The main part of the form. It usually takes up at
least half of the space on the form and contains
captions and areas for entering variable data.
Part of a form that contains any required
signatures.
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Input Design
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Source document zones.
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Input Design
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Input Control
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Input control includes the necessary measures to
ensure that input data is correct, complete, and
secure.
A systems analyst must focus on input control during
every phase of input design, starting with source
documents that promote data accuracy and quality.
A system analyst must take into consideration
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Access – legal channels of getting resources
Identification – to uniquely distinguish a user of a resource
Authentication – to prove positively that the user is what
he/she claims to be.
Authorization – being able to determine and allow the user
only those resources the user has ability to utilize.
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Input Design
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Input Control
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Every piece of information should be traceable back to the input
data
You must provide
Audit trail
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Data security
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Data security protects data from loss or damage and recovers data
when it is lost or damaged.
Records retention policy
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An audit trail records the source of each data item and when it
entered a system. In addition to recording the original source, an
audit trail must show how and when data is accessed or changed,
and by whom. All these actions must be logged in an audit trail file
and monitored carefully.
A records policy that is designed to meet all legal requirements and
business needs for keeping records
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Sequence Summary
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You can reduce input errors by using welldesigned data entry screens and by using data
validation checks that verify data sequence,
existence, range and limit, reasonableness,
validity, combination, and batch controls
You learned about source document design and
the various zones in a source document,
including the heading zone, the control zone,
the instruction zone, the body zone, the totals
zone, and the authorization zone
Finally you learned about input control,
including audit trails, data security, privacy
issues, and records retention policies
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Sequence Summary
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In this Sequence we have
 Explained the validation checks for reducing
input errors including: sequence, existence,
range and limit, reasonableness, validity,
combination, and batch controls
 Explained source document design and the
various zones in a source document, including
the heading zone, the control zone, the
instruction zone, the body zone, the totals
zone, and the authorization zone
 Explained input control, including audit trails,
data security, privacy issues, and records
retention policies
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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.
[2] system analysis and design, sixth edition
Authors: Kenneth E. Kendall and Julie E.
Kendall
Publisher: Prentice Hall
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