SYSTEMS ANALYSIS AND DESIGN TOOLS

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SYSTEMS ANALYSIS AND DESIGN TOOLS

• Analysis Tool
• DATA FLOW DIAGRAMS

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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.

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THE DATA FLOW APPROACH

• When systems analysts attempt to understand he
  information requirements of users, they must be
  able to
• 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.

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ADVANTAGES OF USING DFD

• Freedom from committing to the technical
  implementation of the system too early.
• Further understanding of the interrelatedness of
  systems and subsystems.
• Communicating current system knowledge to users
  through data flow diagrams.
• Analysis of a proposed system to determine if the
  necessary data and processes have been defined.

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CONVECTIONS USED IN DFD

• Four basic symbols are used to chart movement on
  data flow diagrams. They are
• 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.

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CONVECTIONS USED IN DFD
4 BASIC SYMBOLS USED IN DFD
Student
Entity
Flow of data
New Student Information
2.1 Create Student record
Process
Data Store
Student Master
D3
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CONVECTIONS USED IN DFD

• THE DOUBLE SQUARE
• 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.
• 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.
• Each entity is labeled with an appropriate name.

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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.

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CONVECTIONS USED IN DFD

• THE ARROW
• The arrow shows movements of data from one point
  to another, with the head of the arrow pointing
  towards the datas destination.
• Data flows occurring simultaneously can be
  depicted doing just that through the use of
  parallel arrows.
• Since an arrow represents data about a person,
  place or thing, it should be described with a
  noun.

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CONVECTIONS USED IN DFD

• THE RECTANGLE WITH ROUNDED CORNERS
• This is used to show the occurrence of a
  transformation process.
• 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.
• Processes represents work being performed within
  the system and should be named using one of the
  following formats.

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CONVECTIONS USED IN DFD

• THE RECTANGLE WITH ROUNDED CORNERS
• A clear name makes it easier to understand what
  the process is accomplishing.
• Assign the name of the whole system when naming a
  high-level process (Context Level Diagram). eg.
  INVENTORY CONTROL SYSTEM.
• The name of a sub-system, use a name such as
  INVENTORY REPORTING SUBSYTEM.

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CONVECTIONS USED IN DFD

• THE RECTANGLE
• These symbols are drawn only wide enough to allow
  identifying lettering in the rectangle.
• In logical data flow diagrams, the type of
  physical storage (e.g., tape, diskette, cd) is
  not specified.
• At this point the data store symbol is simply
  showing a depository that allows addition and
  retrieval of data
• The data store may represent a manual store, such
  as a filing cabinet, or a computerized file or
  database.

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CONVECTIONS USED IN DFD

• THE RECTANGLE
• Since data store represent a person, place, or
  thing they are named with a noun.
• Temporary data stores, such as scratch paper or a
  temporary computer file, are not included on the
  DFD.
• Give each data store a unique reference number,
  such as, D1, D2, D3, and so on, to identify it
  level.

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RULES FOR DRAWING DATA FLOW DIAGRAMS
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Data Flow should not split into two or more
different data flows.
1
3
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RULES FOR DRAWING DATA FLOW DIAGRAMS
All data flows must EITHER originate or terminate
at a process
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RULES FOR DRAWING DATA FLOW DIAGRAMS
Processes needs to have at least one input data
flow and one output data flow
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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
  birds-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.

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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.

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CREATING THE CONTEXT DIAGRAM

• EXAMPLE

Entity 1
Input A
0 System Name
Entity 3
Output C
Entity 2
Input B
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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 supermarkets stock
  database and this information is printed on the
  customers receipt. It also updates the
  products record in the stock file to indicate
  that the product has been sold.
• Draw a context level diagram using the
  information above.