2. Topics
Introduction
The process of design
Process flow chart
Physical Design
Audit consideration
Cost consideration
3. System Design
System Design is a solution, a “how to” approach to the
creation of a new system.
This phase is composed of several steps.
It provides the understanding and procedural details
necessary for implementing the system recommended in
the feasibility study
Emphasis is on translating the performance
requirements into design specifications.
Design goes through logical and physical stages of
development.
Logical Design reviews the present physical system,
prepares input and output specifications, makes edit,
security and control specifications
Details the implementation plan and prepares a logical
design walkthrough.
4. The process of Design
The design phase focuses on the detailed
implementation of the system recommended in
the feasibility sudy
Emphasis is on translating performance
specifications into design specifications
The design phase is a transition from a user-
oriented document (system proposal) to a
document –oriented to the programmers or
database personnel.
5. Logical and Physical Design
System design goes through two phases of
development
Logical and
Physical
Data flow diagram shows the logical flow of a
system and defines the boundaries of the system
For a candidate system it describes the inputs
(source),outputs(destination),databases(data
stores) and procedures(data flows)-all in a format
that meets the user’s requirements.
6. System Design
The design covers the following
Reviews the current physical system-data flows,
file content,volumes,frequencies etc.
Prepares output specifications- formats, content
and frequency of reports, including terminal
specifications and locations
Prepares input specifications- format, content and
most of the input functions. Flow of the document
from the input data source to the actual input
location
7. System Design
Prepares edit ,security and control specifications
.This includes specifying the rules for edit
correction, back up procedures and the controls that
ensure processing and file integrity.
Specifies the implementation plan
Prepares a logical design walkthrough of the
information flow,output,input, controls and
implementation plan
Reviews ,benefits, costs ,target dates and system
constraints
E.g. Safe deposit schemes in banks or locker system
8. System design goes through logical and physical design
Logical
Design
Physical
Design
System specifications System specifications
Determine
Input/Output
specification
s
File
specification
s
Processing
Specification
s
Data entry /Access
communication
Inquiry
File/Update
maintenance
Backup /Recovery
Master
Transa
ction
Dorm
ant
Scree
ns
I/O
FORM
S
File
Specifi
cations
Repo
rt
layou
t
9. Design the physical system
Specify input/output media
Design the database and specify backup
procedures
Design physical information flow through the system
and a physical design walkthrough
Plan System Implementation
Prepare a conversion schedule and a target date
Determine training procedures ,courses and
timetable
Devise a test and implementation plan and
specify any new hardware /software
Update benefits ,costs ,conversion date and
system constraints (legal, financial, hardware
etc.)
10. Design Methodologies
Improve productivity of analysts and
programmers
Improve documentation and subsequent
maintenance and enhancements
Cut down drastically on cost overruns and delays
Improve communication among the user, analyst
,designer and programmer
Standardize the approach to analysis and design
Simplify design by segmentation
11. Structured Design
It is a data flow based methodology.
The approach begins with a system specifications
that identifies inputs and outputs and describes the
functional aspects of the system.
The system specifications ,then are used as a
basis for the graphic representations –DFD , Data
flows and processes
From the DFD, the next step is the definition of
the modules and their relationships to one another
in a form called a Structured Chart ,using a data
dictionary and other structured tools
12. The Structured Design Method
System Specifications DFD Data Dictionary
Structured
English, Decision
Tree, Decision
Table
Process Information
13. Decomposition-A framework
Structured Design partitions a program into small,
independent modules.
They are arranged in a hierarchy that
approximates a model of the business area and is
organized in a top-down manner with the details .
Structured design is an attempt to minimize
complexity and make a problem manageable by
subdividing it into smaller segments which is
called modularization or decomposition
14. Advantages of structured Design
Critical interfaces are tested first
Early versions of the design , though incomplete
are useful enough to look like the real system
Structuring the design provides control and
improves morale
The procedural characteristics define the order
that determines processing.
15. Functional Decomposition
The documentation tool for structured design is
the hierarchy or structure chart.
It is a graphic tool for representing hierarchy and
it has three elements
Module
Connection
Coupling
17. Connection
Represented by a vector linking two modules.it
usually means one module has called another
module.
A
B C
Module A calls B and C
18. Coupling
The couple is represented by an arrow with a
circular tail. it represents data items moved from
one module to another.
19. System Design Methodologies
In structured design a hierarchy chart represents
a good program design if it meets the criteria of
cohesion and coupling.
Each module performs a single
function(cohesion) and should be independent of
the rest of the program(coupling)
Each criterion calls for more details than are
available.
This prompts the analyst to develop
input/process/output(IPO) Charts for each module
in the hierarchy chart.
20. HIPO and IPO Chart
HIPO is a forms driven technique in that standard
froms are used to document the information.
It consists of hierarchy chart and an associated
set of input/process/output charts
HIPO captures the essence of top-down
decomposition
It describes the data input and output from
processes and defines the data flow composition.
Developed by IBM as a design aid and
implementation technique with the following
objectives:
21. HIPO Chart Objectives
Provide a structure by which the functions of a system
can be understood.
State the functions to be performed by the program
rather than specifying the program statements to be
used to perform the functions
Provide a visual description of input to be used and
output to be produced for each level of the diagram.
HIPO makes the transformation of Input to output
data visible.
HIPO uses easy-to-draw vector like symbols between
processes that define data communications and data
directions.
22. Structured walkthrough
An activity of all phases of a structured project is
the walkthrough.
It is an interchange of ideas among peers who
review a product presented by its author(s) and
agree on the validity of a proposed solution to a
problem.
23. User Involvement
Walkthrough may be held at various points in the
system development life cycle.
The probability of success improves with the
user’s interest and involvement in the design of
the system.
24. Audit Consideration
A well designed system should have controls to
ensure proper operation and routine auditing.
A candidate system’s failure often results from a lack
of emphasis on data control.
Standards of accuracy and maintainability must be
specified to eliminate errors and control for fraud.
A system design introduces new control elements
and changes the control procedures.
New controls in the form of relational comparisons are
designed to detect and check errors that arise from
the use of the system
In a manual system ,internal control depends on
human judgement, personal care and division labor.
25. Processing Controls and Data Validation
Several methods have been devised to control
processing activities.
