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Function Modeling & Information Flow

Information is transformed as it flows through a computer-

based system. The system accepts input in a variety of forms;

applies hardware, software, and human elements to transform

it; and produces output in a variety of forms

Structured analysis began as an information flow modeling

technique.

A rectangle is used to represent an external entity (software,

hardware, a person)

A circle (sometimes called a bubble) represents aprocess or

transform that is applied to data (or control) and changes it in

some way.

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An arrow represents one or more data items (data objects) and

it should be labeled.

All arrows on a data flow diagram should be labeled.

The double line represents a data store

stored informationthat is used by the software.

First data flow model (sometimes called a level 0 DFD or

context diagram) represents the entire system.

It provides incremental detail with each subsequent level. It is important not to confuse a DFD with the flowchart.

Function Modeling & Information Flow

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Information Flow model

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Data Flow Diagrams

A data flow diagram is a graphical representation

that depicts information flow andthe transformsthat are applied as data move from input to

output. The basic form of a data flow diagram is also

known as a data flow graph or a bubble chart

It enables software engineer to develop models

of the information domain and functional domainat the same time. Data flow diagram may be used to represent a

system or software at any level of abstraction

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Notations in DFDs

Data Flow Diagrams show the passage of data through

the system by using fine basic constructs1) Data Flow

It shows flow of data from a source to a destination. It isshown with an arrowed line with the arrowhead showing

the direction of flow.

name of flow

It can move from an external entity to a process, from aprocess to another process, into and out of a store from aprocess, and from a process to an external entity as well.

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2) Processes:

These are transformations which change

incoming data flow into outgoing data flow.They are drawn in circular boxes:

The name of the process should describe what

may happen to the data as it passes through the

process.

Process

name

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3) Data/Stores

It is repository of data, that is, a file or

database

It is represented by two parallel lines and

between those lines name of data store is

mentioned

Data store name

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4) External entities:

They are external data processing units which

represent some external process, outside of the

regular data flow .They rely outside the system

boundaries.

5) Resource store:

It represents process with resource flow. It

represents flow of material than data.

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Information flow refinement

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DFD Guidelines

Depict the system as single bubble in level 0.

Primary input and output should be carefully noted

Refine by isolating candidate processes and their associated,data objects and data stores

Each of the bubbles may be refined or layered to depict moredetail

All arrows and bubbles should be labeled with meaningfulnames.

Information flow continuity must be maintained from levelto level.

One bubble at a time should be refined.

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Data flow models

A level 0 DFD, also called afundamental system model or a

context model, represents the entire software element as a

single bubble with input and output data indicated by incoming

and outgoing arrows.

Level 0 DFD refinement into level 1 DFD with all relevant

processes to the system.

Level 1 DFD each processes can be refined into level 2 DFD.

Refinement of DFD continues until each bubble performs a

simple function.

d i

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Order processing DFD