System Analysis and Design Data Flow Diagram System Analysis and Design 1

1System Analysis and Design

Data Flow Diagram

System Analysis and Design

2 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


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


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

System Analysis and DesignSlide 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


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.

Context Diagrams


Developing DFDs1 .Context Diagram for Pizza Hut food ordering

system

CUSTOMER KITCHEN

RESTAURANTMANAGER

FoodOrderingSystem

0

Customer Order

Receipt

Food Order

Management Reports


Creating a Set of DFDsCreate a graphical model of the

information system based on your fact-finding results

Performing three main tasksStep 1: Draw a context diagramStep 2: Draw a diagram 0 DFDStep 3: Draw the lower-level diagrams

8


Creating a Set of DFDs Draw a Diagram 0 DFD

Diagram 0Zooms in on the context diagram and shows

major processes, data flows, and data storesMust retain all the connections that flow into

and out of process 0Each process has a reference numberDiverging data flow

9


Creating a Set of DFDsDraw the Lower-Level Diagrams

Must use leveling and balancing techniques

LevelingUses a series of increasingly detailed DFDs to

describe an information systemExploding, partitioning, or decomposing

10


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


Developing DFDs1 .Context Diagram for Pizza Hut food ordering

system

CUSTOMER KITCHEN

RESTAURANTMANAGER

FoodOrderingSystem

0

Customer Order

Receipt

Food Order

Management Reports


Developing DFDs2 .Level-0 Diagram for Pizza Hut food ordering

system

CUSTOMER KITCHEN

manager

1.0Receive &

TransformCustomer

Food Order

3.0

UpdateInventory

File

2.0

UpdateGoods Sold

File

D1 Inventory File D2 Goods Sold File

4.0

ProduceManagement

Report

Customer Order

Receipt Food Order

InventoryDataGoods Sold

FormattedInventory Data

FormattedGoods Sold Data

Daily Goods Sold AmountsDaily Inventory Depletion Amounts

Management Reports


Developing DFDs2 .Level-1 Diagram for Pizza Hut food ordering

system1.1

ReceiveCustomer

Order

1.3TransformOrder toKitchenFormat

1.2

GenerateCustomerReceipt

1.4

GenerateGoods SoldIncrements

1.5

GenerateInventory

Decrements

CustomerOrder

CustomerOrder Food Order

CustomerOrder

Customer Order

Customer Order Inventory Data

Goods Sold DataReceipt


Rules Governing Data Flow Diagramming


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


Rule 2:• No Process can have only inputs• If an object has only inputs, then it

must be a sink.



Rule 3:• A Process should have a verb phrase

label

GenerateOrders



Rule 4:• Data cannot move directly from one

data store to another data store.• Data must be moved by a process

GenerateOrders




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

GenerateOrdersSource Source



Rule 6:• Data cannot move directly to an

outside sink from a data store• Data must be moved by a process

GenerateOrders SinkSink



Rule 7:• A data store has a noun phrase label

Inventory



Rule 8:–A data store A data store must have at least

one incoming and one outgoing data flow.

Inventory



Source/SinkRule 9:• Data cannot move directly from a

source to a sink• It must be moved by a process

SinkSource Source SinkGenerateOrders



Source/Sink

Rule 10:• A source/sink has a noun phrase

Supplier



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

GenerateOrders

GenerateOrders



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



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



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

AA

B

C



Data flow

Rule 15:• A data flow to a data store means

update (delete or change)

GenerateOrders

Delete or changed

data



Data flow

Rule 16:• A data flow from a data store means

retrieve or use

GenerateOrders

Retrieve/Use


Data flow

Rule 17:• A data flow must have a noun phase

label

Updated stock



DFDs Exercises

System Analysis and Design34

Data Flow Diagrams

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


Data Flow Diagrams


Data Flow Diagrams

•Entity can be connected with a process only

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


Data Flow Diagrams


Data Flow Diagrams


DFD Errors


DFD Errors

Documents

System Analysis and Design Data Flow Diagram System Analysis and Design 1