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SYSTEM ANALYSIS AND DESIGNChap 7: using Data Flow Diagrams
AITS-MCA- Kiran Ajudiya
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Data Flow Diagrams (DFD) Through a structure analysis technique
called data flow diagram. Analyzing data-oriented systems
Inputs Processes outputs
Emphasizes system logic
AITS-MCA- Kiran Ajudiya
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Advantages Freedom from technical commitment
(neutral) Clarify systems / subsystems (is this right?) Communicates understanding to users (is
this right?) Analysis of systems (is anything missing?)
AITS-MCA- Kiran Ajudiya
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Conventions (cont) Entity (source / destination: person, dept, machine, business) Arrow (data flow: from->to)
Process (transforming) Data store (examination, retrieval, addition)
AITS-MCA- Kiran Ajudiya
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Conventions: Basic Symbols
AITS-MCA- Kiran Ajudiya
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DFD Development : Basic Rules
AITS-MCA- Kiran Ajudiya
DFD must have at least one process. Process must receive at least one
data flow and at least one leaving from the process.
Data store should be connected to at least one process.
External entities should not connected each other.
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Process Naming:
Inventory Control System Name reflects whole systemInventory reporting subsystem Name reflects whole subsystemVerify Customer Account Name reflects specific process
AITS-MCA- Kiran Ajudiya
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AITS-MCA- Kiran Ajudiya
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Creating Context Diagram
AITS-MCA- Kiran Ajudiya
Contains only one process (number Zero).
Representing the entire system (input – process – output).
All external entities are shown on the context diagram.
Show major data flow. Diagram does not contain any data
store
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Context Diagram
AITS-MCA- Kiran Ajudiya
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Diagram 0 (Next Level)
AITS-MCA- Kiran Ajudiya
Diagram 0 is the explosion of the context diagram. May include up to 9 Process. Start with the data flow from an entity on input
side (Forward) Work backward from output (Backward) Examine Data Flow:
What processes put data into the store? What processes use the data?
Analyze well define process What input & output, appropriate connection or not
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Diagram 0 (parent)
AITS-MCA- Kiran Ajudiya
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Child Diagram
AITS-MCA- Kiran Ajudiya
Each process on diagram 0(zero) may be exploded to create a child diagram.
Each process on a lower-level diagram may be exploded to create another child diagram.
Each process is numbered with the parent diagram number, a period, and a unique child diagram number.
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Child Diagram (Continue….)
AITS-MCA- Kiran Ajudiya
External entities are usually not shown on the child diagrams below Diagram 0.
If the parent process has data flow connecting to a data store, the child diagram may include the data store as well.
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Child Diagram (Continue…)
AITS-MCA- Kiran Ajudiya
A lower-level diagram may contain data stores not shown on the parent process, such as: A file containing a table of information
(such as a tax table). A file linking two processes on the child
diagram. Minor data flow, such as an error line,
may be included on a child diagram. An interface data flow is data that are
input or output from a child diagram that matches the parent diagram data flow.
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Child Diagram (Continue…..)
AITS-MCA- Kiran Ajudiya
Processes may or may not be exploded depending on their level of complexity when a processes is not exploded it is said to be functionally primitive and is called a “PRIMITIVE PROCESS”
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AITS-MCA- Kiran Ajudiya
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Typical Errors in DFD Data flow arrow wrong direction /
forgetting Connecting Data store to entity w/o
process Incorrect labeling Too many processes (>9 on a sheet) Omitting data flow Creating Unbalanced decomposition in
child diagram.AITS-MCA- Kiran Ajudiya
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Bad!AITS-MCA- Kiran Ajudiya
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Good!
AITS-MCA- Kiran Ajudiya
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Logical & physical Data Flow
AITS-MCA- Kiran Ajudiya
Logical DFD focused on business and how business operates.
It is not worried how the system will be constructed.
Physical DFD shows how the system will be implemented including hardware, software, files and people involved in the system.
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Transitions
AITS-MCA- Kiran Ajudiya
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Logical vs Physical Data Flow
AITS-MCA- Kiran Ajudiya
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Developing Logical Flow Diagrams Advantages
Better communication w/users Stable systems Understanding of business Flexibility and maintenance Identify redundancies
AITS-MCA- Kiran Ajudiya
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Developing Physical DFD
AITS-MCA- Kiran Ajudiya
Clarifying which processes are performed by human and which are automated.
Describing processes in more detail than logical DFD
Sequencing processes that have to be done in a particular order.
Identifying temporary data stores. Specifying actual names of files database tables
and printouts Adding controls to ensure the process are done
properly.
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AITS-MCA- Kiran Ajudiya
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AITS-MCA- Kiran Ajudiya
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AITS-MCA- Kiran Ajudiya
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Partitioning Data Flow Diagram
AITS-MCA- Kiran Ajudiya
Partitioning is the process of examining a data flow diagram and detecting how it should be divided into collection of manual process and collection of computer programs.
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Reason for partitioning DFD
AITS-MCA- Kiran Ajudiya
Different user group Timing Similar tasks Efficiency (Report) Reliability of data (Credit Card) Security (Net Banking)
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CRUD Matrix
AITS-MCA- Kiran Ajudiya
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Event Response Table
AITS-MCA- Kiran Ajudiya
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Data Flow Diagrams
AITS-MCA- Kiran Ajudiya
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Data Flow Diagram
AITS-MCA- Kiran Ajudiya
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Data Flow Diagram
AITS-MCA- Kiran Ajudiya
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Use Case and Flow Diagrams
AITS-MCA- Kiran Ajudiya
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In class example
AITS-MCA- Kiran Ajudiya