Using data flow diagram

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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


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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?)


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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)


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Conventions: Basic Symbols


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DFD Development : Basic Rules


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


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Creating Context Diagram


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


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Diagram 0 (Next Level)


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)


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Child Diagram


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….)


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…)


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…..)


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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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!


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Logical & physical Data Flow


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


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Logical vs Physical Data Flow


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Developing Logical Flow Diagrams Advantages

Better communication w/users Stable systems Understanding of business Flexibility and maintenance Identify redundancies


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Developing Physical DFD


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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Partitioning Data Flow Diagram


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


Different user group Timing Similar tasks Efficiency (Report) Reliability of data (Credit Card) Security (Net Banking)

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CRUD Matrix


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Event Response Table


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Data Flow Diagrams


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Data Flow Diagram


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Data Flow Diagram


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Use Case and Flow Diagrams


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In class example


Using data flow diagram

Education

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