Systems Analysis – Analyzing
Requirements
 Analyzing
requirement stage identifies
user information needs and new systems
requirements
 IS dev team responsibility to ensure the
new system serve the needs of org
 Determining accurate user needs and
system requirement is important because
the design of new system is based on
these requirements
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Structured analysis, a dominant technique
for documenting user requirements
It provides methods to analysts for
analyzing, organizing, controlling and
documenting large complex IS
Structured analysis is appropriate for
business IS because these systems are
predominantly data-driven systems
To document IS data and data
transformation, structured analysis uses
Data Flow Diagram
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Description of system problems and solutions
are written in narrative form
Graphic presentations may be used to enhance
the problem description
Data flow diagram is a graphic presentation of
external entities, data movement, processing
functions and data stores necessary to support an
IS
DFD is popularized using structured analysis and
design approach
The purpose of diagramming is that any person
would be able to understand the system by just
looking at the diagram
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Four symbols used in DFD (Yourdon
symbols):
– A circle
• Indicate some process or transformation of data
• Process shows what a system does
• Each process has data input and output
• A process name should consist of one single phrase and
should define a specific action rather than general process
• The name and number appear inside the circle
– A pair of parallel lines
• To indicate data store
• Process can enter data or retrieve data from data store
• A rectangle
 To indicate external entity
 Entity – person, department, system or org out of the
system
 The system interacts with these entities
• An arrow
 Indicate flow of data
 Arrow pointing to a data store indicates writing or
updating to data store
 Arrow coming out of data store shows reading
process
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DFD are organized hierarchically
There is a master DFD (context DFD)
followed by subDFD
Context DFD
– First diagram that displays the least amount of detail
– Used to identify system boundary and its
relationship to the entities
– Has only one process labeled with the system’s
name
– The entities that interact with the system are shown
with their labeled data flows
– No data stores are shown
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Context DFD show system in general, therefore
there is a need to “explode” into other DFD
Intermediate DFD will show the sequence of
processes done by the system together with data
stores accessed by the processes
Each process is given number depicting their
sequence of occurrence
An important characteristics of all DFD: anything
represented on the previous level must also be
represented on all levels that follow
All entities in context DFD must also appear on
all levels that follow
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It is not a good idea to include all details in
one DFD because it would be too large
It would be too large that it would be
difficult to understand and the DFD then no
longer serve as a comm tool
This is why the context level DFD needs to
“explode” into intermediate DFD
The processes must be numbered to show
sequence in which they are being
performed
The process name should define a specific
action rather than a general process
 Data
stores not shown in context DFD are
drawn in intermediate DFD
 When naming a data store, use specific
names and avoid general terms
 The DFD does not indicate which media
the data are being stored
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What is a good DFD?
– The word in the process symbol in the context
DFD is the name of the system
– Context DFD should possess one process
symbol only
– Data store symbols should not appear in the
context DFD
– The first word in the process symbol in
intermediate DFD must begin with a verb
followed by a descriptive noun
– Processes must be numbered
– Label clearly all data flows, entities, data stores
and processes. No need to label data flows from
process to process but it is a good practice to do
so
– The arrow direction for the data flows must be
correct
– Crossing of lines will not be allowed. You are to
duplicate entities and data stores where
necessary
– No incorrect connections
 Characteristics
of good diagrams
• Should be graphical with supporting textual
detail
• Should allow the system to be viewed top-down,
partitioned fashion
• Should have minimal redundancy
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Two technologies offering increase in
productivity of IS dev are
– Computer aided software engineering (CASE)
– Object-oriented development technology
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CASE assist IS dev team in planning,
analyzing, designing, programming and
maintaining IS
The principal advantage of CASE is that it
offers an integrated packages of
capabilities for several of these tasks
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CASE provides automatic assistance for
checking the consistency and completeness
of the system
The availability of this info makes it easier to
introduce modifications in a consistent
manner at any time during dev or
maintenance phase
CASE provides good platform for quick app
dev through prototyping.
It helps to dev hierarchy of menus for the
user interface and specify screens and
reports all done in consultation with the
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Prototyping tools include report writers, query
languages, screen generators and 4GL
A report writer is a nonprocedural language for
producing reports from data in a data base
A query language is a nonprocedural language for
retrieving, sorting adding and presenting data from a
database
a screen generator is a software for generating and
maintaining display and data entry for screen forms
A program generator is a software toll that generates a
second or third language program
4GL has both procedural and nonprocedural features
allowing programmers to write programs faster and
accurately
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A central repository stores, analyzes,
updates and reports on the info about the
system.
The central repository can be used to
analyze the DFD for balance and also print a
report of the DFD
Command can be issued to delete
components of DFD or manipulate the
positions of the components
Processes can be expanded into lower level
DFD
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A data design tool will assist in design phase to
model files and database
CASE will maintain Entity Relationship Diagram
(ERD) of the system
Tools will make up the various input modes
An evaluation mode is available to check models
for consistencies or to suggest changes
A reporting mode is used to produce listings and
describe the model object sets and attributes to
draw ERD
A generation mode will help create database
definitions from the model
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The user input the ERD by entering all known
attributes as a volume input
ERD itself will be drawn by entering the entity
and the relationship sets and adding attributes to
them
The modeling tool guides the user towards
developing a model
A programming tool will assist in writing out the
programs which include code generators,
program debuggers and testing modules
A project mgt tool assists in scheduling the IS
project
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CASE contribute to improving maintenance
of IS
The use of CASE during early task means
better documented systems in repository
and thus easy to maintain
It is possible to trace a user request for an
enhancement from DFD to program coding
modules and determine the impact of
changes
CASE makes it possible to maintain system
specification as they are changed during
maintenance
 CASE
is a complex technology requiring
learning
 The complexity of CASE and lack of
integrated support limited the adoption
 CASE tools make systems dev team
better and more effective but they are not
a substitute
 Skills and experience cannot be
automated
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Management together with system steering
committee will review the analysis report
The review is to determine if work on the
proposed system should proceed to the
next phase
The problems identified and solutions to
overcome will be documented in the
systems analysis report together with the
diagrams used to document the existing
system
You may also need to present the analysis
findings