Transcript SYSTEMS ANALYSIS AND DESIGN TOOLS

SYSTEMS ANALYSIS
AND DESIGN TOOLS
Analysis Tool
DATA FLOW DIAGRAMS
INTRODUCTION
 Data Flow diagrams graphically characterize
data processes and flows in a business system.
 In their original state data flow diagrams depict
the broadest possible overview of system inputs,
processes and outputs, which correspond to
those of the general systems model discussed.
 A series of layered data flow diagrams may also
be used to represent and analyze detailed
procedures within a larger system.
THE DATA FLOW APPROACH
 When systems analysts attempt to understand he
information requirements of users, they must be able to
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conceptualize how data moves through the organization,
the processes or transformation that the data undergoes
what the outputs are
 The data flow approach emphasizes the logic underlying
the system.
 By using combinations of only four symbols, the systems
analyst can create a pictorial depiction of processes that
will eventually provide solid system foundation.
ADVANTAGES OF USING DFD
1.
Freedom from committing to the technical
implementation of the system too early.
2.
Further understanding of the interrelatedness of
systems and subsystems.
3.
Communicating current system knowledge to users
through data flow diagrams.
4.
Analysis of a proposed system to determine if the
necessary data and processes have been defined.
CONVECTIONS USED IN DFD
 Four basic symbols are used to chart movement on data
flow diagrams. They are:
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A Double Square
An arrow
A rectangle with rounded corners
A rectangle
 An entire system and sub-system can be depicted
graphically with these four symbols in combination.
CONVECTIONS USED IN DFD
4 BASIC SYMBOLS USED IN DFD
Entity
Flow of
data
Student
New Student
Information
2.1
Process
Data Store
Create
Student
record
D3 Student Master
CONVECTIONS USED IN DFD
THE DOUBLE SQUARE
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This is used to depict an external entity (another
department, a business, a person or a machine)
that can send data to or receive data from the
system.
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The external entity or entity, is also called a
source or destination of data, and it is considered
to be external to the system being described.
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Each entity is labeled with an appropriate name.
CONVECTIONS USED IN DFD
THE DOUBLE SQUARE
 Although it acts with the system it is considered
as outside of the boundaries of the system.
 Entities should be named with a noun.
 The same entity may be used more than once
on the same data flow diagram, to avoid
crossing data flow line.
CONVECTIONS USED IN DFD
THE ARROW
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The arrow shows movements of data from one point to
another, with the head of the arrow pointing towards the
data’s destination.
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Data flows occurring simultaneously can be depicted
doing just that through the use of parallel arrows.
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Since an arrow represents data about a person, place or
thing, it should be described with a noun.
CONVECTIONS USED IN DFD
THE RECTANGLE WITH ROUNDED CORNERS
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This is used to show the occurrence of a transformation
process.
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Processes always denote a change in or transformation
of data; hence, the data leaving a process is always
labeled differently from the one entering it.
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Processes represents work being performed within the
system and should be named using one of the following
formats.
CONVECTIONS USED IN DFD
THE RECTANGLE WITH ROUNDED CORNERS
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A clear name makes it easier to understand what the
process is accomplishing.
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Assign the name of the whole system when naming a
high-level process (Context Level Diagram). eg.
INVENTORY CONTROL SYSTEM.
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The name of a sub-system, use a name such as
INVENTORY REPORTING SUBSYTEM.
CONVECTIONS USED IN DFD
THE RECTANGLE
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These symbols are drawn only wide enough to allow identifying
lettering in the rectangle.
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In logical data flow diagrams, the type of physical storage (e.g.,
tape, diskette, cd) is not specified.
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At this point the data store symbol is simply showing a
depository that allows addition and retrieval of data
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The data store may represent a manual store, such as a filing
cabinet, or a computerized file or database.
CONVECTIONS USED IN DFD
THE RECTANGLE
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Since data store represent a person, place, or thing they
are named with a noun.
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Temporary data stores, such as scratch paper or a
temporary computer file, are not included on the DFD.
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Give each data store a unique reference number, such
as, D1, D2, D3, and so on, to identify it level.
RULES FOR DRAWING DATA
FLOW DIAGRAMS
2
1
3
Data Flow should
not split into two or
more different data
flows.
RULES FOR DRAWING DATA
FLOW DIAGRAMS
All data flows must
EITHER originate or
terminate at a
process
RULES FOR DRAWING DATA
FLOW DIAGRAMS
Processes needs to
have at least one
input data flow and
one output data
flow
CREATING THE CONTEXT
DIAGRAM
• This is an overview, one including basic inputs,
The general system and outputs.
• This will be the most general diagram – really, a
bird’s-eye view of data movement in the system
and the broadest possible conceptualization of
the system.
• The context diagram is the highest level in a dat
flow diagram and contains only one process,
representing the entire system.
CREATING THE CONTEXT
DIAGRAM
• The process is given the number 0.
• All external entities are shown on the contest
diagram, as well as major data flow to and from
them.
• The diagram does not contain any data stores
and is fairly simple to create, once the external
entities and the data flow to and from them are
known to analysts from interviews with users
and as a result to document analysis.
CREATING THE CONTEXT
DIAGRAM
EXAMPLE
Entity
1
Input A
0
Output C
System Name
Entity
2
Input B
Entity
3
Question
A supermarket uses a Point of Sale (POS) terminal to keep track of the goods that is in stock
and to produce bills for customers. Whenever an item is sold, the product code of the
item is read by a barcode scanner. The price and name of the product is checked in
the supermarket’s stock database and this information is printed on the customer’s
receipt. It also updates the product’s record in the stock file to indicate that the product
has been sold.
Draw a context level diagram using the information above.