System Analysis and Design

Data Flow Diagram

System Analysis and Design

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System Analysis and Design

Data Flow diagram

• The dataflow diagram is a modeling tool that allows us to picture a system as a network of functional processes, connected to one another by “pipelines” and “holding tanks” of data

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System Analysis and Design

Data Flow Diagrams

• Context Diagrams

– Top-level view of an information system that shows the system’s boundaries and scope

– Do not show any data stores in a context diagram because data stores are internal to the system.

– Begin by reviewing the system requirements to identify all external data sources and destinations

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System Analysis and Design

Context Diagrams

– Record the name of the entities and the name and

content of the data flows, and the direction of the data flows.

– What makes one system more complex than another is the number of components, the number of levels, and the degree of interaction among its processes, entities, data stores, and data flows

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System Analysis and Design Slide 5

• Shows the overall business process as just one process.

• The process is given the number zero.

• Shows all the outside entities that receive information from or contribute information to the system

Context Diagrams

System Analysis and Design

1. Each context diagram must fit on one page.

2. The process name in the context diagram should be the name of the information system.

3. Use unique names within each set of symbols.

4. Do not cross lines.

5. Use a unique reference number for each process symbol.

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Context Diagrams

System Analysis and Design

Developing DFDs 1. Context Diagram for Pizza Hut food ordering system

CUSTOMER KITCHEN

RESTAURANT MANAGER

Food Ordering System

0

Customer Order

Receipt

Food Order

Management Reports

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System Analysis and Design

Creating a Set of DFDs

Create a graphical model of the information system based on your fact-finding results

Performing three main tasks

Step 1: Draw a context diagram

Step 2: Draw a diagram 0 DFD

Step 3: Draw the lower-level diagrams

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System Analysis and Design

Creating a Set of DFDs

Draw a Diagram 0 DFD

Diagram 0

Zooms in on the context diagram and shows major processes, data flows, and data stores

Must retain all the connections that flow into and out of process 0

Each process has a reference number

Diverging data flow

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System Analysis and Design

Creating a Set of DFDs

Draw the Lower-Level Diagrams

Must use leveling and balancing techniques

Leveling Uses a series of increasingly detailed DFDs to

describe an information system

Exploding, partitioning, or decomposing

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System Analysis and Design

Data Flow Diagrams

• Lower-Level Diagrams

–Balancing

• Ensures that the input and output data flows of the parent DFD are maintained on the child DFD

System Analysis and Design

Developing DFDs 1. Context Diagram for Pizza Hut food ordering system

CUSTOMER KITCHEN

RESTAURANT MANAGER

Food Ordering System

0

Customer Order

Receipt

Food Order

Management Reports

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System Analysis and Design

Developing DFDs 2. Level-0 Diagram for Pizza Hut food ordering system

CUSTOMER KITCHEN

manager

1.0 Receive & Transform Customer

Food Order

3.0

Update Inventory

File

2.0

Update Goods Sold

File

D1 Inventory File D2 Goods Sold File

4.0

Produce Management

Report

Customer Order

Receipt Food Order

Inventory Data Goods Sold

Formatted Inventory Data

Formatted Goods Sold Data

Daily Goods Sold Amounts Daily Inventory Depletion Amounts

Management Reports

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System Analysis and Design

Developing DFDs 2. Level-1 Diagram for Pizza Hut food ordering system

1.1

Receive Customer

Order

1.3 Transform Order to Kitchen Format

1.2

Generate Customer

Receipt

1.4

Generate Goods Sold Increments

1.5

Generate Inventory

Decrements

Customer Order

Customer Order Food Order

Customer Order

Customer Order

Customer Order Inventory Data

Goods Sold Data Receipt

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System Analysis and Design

Rules Governing Data Flow

Diagramming

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System Analysis and Design

Rules Governing Data Flow Diagramming Process

Rule 1:

• Process cannot have outputs only. It means it is making data from nothing

• Only a source should have outputs without inputs

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System Analysis and Design

Rule 2:

• No Process can have only inputs

• If an object has only inputs, then it must be a sink.

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Rules Governing Data Flow Diagramming Process

System Analysis and Design

Rule 3:

• A Process should have a verb phrase label

Generate Orders

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Rules Governing Data Flow Diagramming Process

System Analysis and Design

Rule 4:

• Data cannot move directly from one data store to another data store.

• Data must be moved by a process

Generate Orders

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Rules Governing Data Flow Diagramming Process

System Analysis and Design

Rules Governing Data Flow

Diagramming Process

Rule 5: • Data cannot move directly from an

outside source to a data store • Data must be moved by a process

which receives data from the source and places the data into the data store

Generate Orders Source Source

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System Analysis and Design

Rules Governing Data Flow

Diagramming Process

Rule 6:

• Data cannot move directly to an outside sink from a data store

• Data must be moved by a process

Generate Orders Sink Sink

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System Analysis and Design

Rules Governing Data Flow

Diagramming Process

Rule 7:

• A data store has a noun phrase label

Inventory

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System Analysis and Design

Rules Governing Data Flow

Diagramming Process

Rule 8:

–A data store A data store must have at least one incoming and one outgoing data flow.

Inventory

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System Analysis and Design

Rules Governing Data Flow

Diagramming Process Source/Sink

Rule 9:

• Data cannot move directly from a source to a sink

• It must be moved by a process

Sink Source Source Sink Generate

Orders

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System Analysis and Design

Rules Governing Data Flow

Diagramming Process Source/Sink

Rule 10:

• A source/sink has a noun phrase

Supplier

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System Analysis and Design

Rules Governing Data Flow

Diagramming Process Data flow

Rule 11:

• A data flow has only one direction of flow between symbols

• It may have both direction flows between a process and a data store to show a read before an update

• Later it is indicated by two separate arrows

Generate Orders

Generate Orders

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System Analysis and Design

Rules Governing Data Flow

Diagramming Process

Data flow Rule 12:

• A fork in a data flow means that exactly the same data goes from a common location to two or more different processes, data stores, or sources/sinks.

• There should not be a variation in duplication

A

B

A

A 27

System Analysis and Design

Rules Governing Data Flow

Diagramming Process Data flow Rule 13:

• A joint in a data flow means that exactly the same data comes from any of two or more different processes, data stores, or sources/sink to a common location

• Only similar data flows can be joined

A

B

A

A

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System Analysis and Design

Rules Governing Data Flow

Diagramming Process Data flow Rule 14:

• A data flow cannot go directly to the same process it leaves.

• There must be at least one other process which handles the data flow, produces some other data flow, and returns the original data flow to the beginning process

A

A A

B

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System Analysis and Design

Rules Governing Data Flow

Diagramming Process Data flow Rule 15:

• A data flow to a data store means update (delete or change)

Generate Orders

Delete or

changed

data

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System Analysis and Design

Rules Governing Data Flow

Diagramming Process

Data flow Rule 16:

• A data flow from a data store means retrieve or use

Generate Orders

Retrieve/Use

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System Analysis and Design

Data flow Rule 17:

• A data flow must have a noun phase label

Updated stock

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Rules Governing Data Flow

Diagramming Process

System Analysis and Design

DFDs Exercises

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System Analysis and Design 34

Data Flow Diagrams

Examples of correct uses of data store symbols in a data flow diagram. [1]

System Analysis and Design 35

Data Flow Diagrams

System Analysis and Design 36

Data Flow Diagrams

•Entity can be connected with a process only

Examples of correct uses of external entities in a data flow diagram.[1]

System Analysis and Design 37

Data Flow Diagrams

System Analysis and Design 38

Data Flow Diagrams

System Analysis and Design

DFD Errors

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System Analysis and Design

DFD Errors

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