Management Information Systems

Process ModelingProcess Modeling

Dr Amr Eltawil

Data Flow Diagrams

DFDDFD

Learning Objectives

U d t d th l i l d li fUnderstand the logical modeling of processes through studying data flow diagramsH t d d t fl di i l dHow to draw data flow diagrams using rules and guidelinesH t d d t fl di i tHow to decompose data flow diagrams into lower-level diagramsB l i f d t fl diBalancing of data flow diagramsDiscuss the use of data flow diagrams as

l i t lanalysis tools Represent processing logic using Structured E li h d d i i t bl

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English and decision tables5.25.2

Process Modeling

Graphically represent the processes that capture, manipulate, store and distribute data between a system and its environment and among system components

Data flow diagrams (DFD)Graphically illustrate movement of data between p yexternal entities and the processes and data stores within a system

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5.35.3

A DFD example

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DFD Symbols

Data FlowDepicts data that are in pmotion and moving as a unit from one place to another in pthe system

Drawn as an arrowDrawn as an arrow

Select a meaningful name to represent the datarepresent the data

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5.55.5

DFD Symbols

ProcessDepicts work or action pperformed on data so that they are transformed, stored y ,or distributed

Drawn as a rectangle withDrawn as a rectangle with rounded corners

Number of process as well asNumber of process as well as name are recorded

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5.65.6

Data Flow Diagramming Symbols

D t StData StoreDepicts data at restMay represent data in:

File folderComputer-based fileNotebook

Drawn as a rectangle with the right hand vertical line missingLabel includes name of the store as well as the number

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5.75.7

Data Flow Diagramming Symbols

S /Si kSource/SinkDepicts the origin and/or destination of the datadestination of the dataSometimes referred to as an external entityyDrawn as a square symbolName states what the external agent isBecause they are external, many characteristics are not of interestcharacteristics are not of interest to us

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5.85.8

A DFD example

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5.95.9

Data Flow Diagramming Definitions

Context DiagramA data flow diagram (DFD) of the scope of an organizational system that shows the system boundaries, external entities that interact with the system and the major information flows between thesystem and the major information flows between the entities and the system

Level 0 DiagramLevel-0 DiagramA data flow diagrams (DFD) that represents a system’s major processes data flows and data storessystem s major processes, data flows and data stores at a higher level

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5.105.10

The system consists of many subsystems

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Decomposition of DFDs

Functional decompositionAct of going from oneg gsingle system to many component processesy p p

Repetitive procedure

Lowest level is called a primitive DFDLowest level is called a primitive DFD

When decomposing a DFD, you musti t t d t t fconserve inputs to and outputs from a

process at the next level of decomposition

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5.125.12

Decomposition of DFDs

Level-N DiagramsA DFD that is the resultA DFD that is the result of n nested decompositions of a series of sub-processes from a process on a level-0 diagram

Rules for stopping decompositionWhen each process has been reduced to a single decision, calculation or database operation

When each data store represents data about a single entity

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5.135.13When the system user does not care to see any more detail

Developing DFDs: A Take Away Example

The customer initiates food ordersThe customer initiates food orders

The system generates customer receipts.p

The system generates food orders to the kitchen.

The system generates management reports.

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5.145.14

Developing DFDs: An Example

N t t i t dNext step is to expand the context diagram to show the breakdown of processes.Level n DFDInputs to a process are always different than outputsoutputsObjects always have a unique nameq

In order to keep the diagram uncluttered, you can repeat data stores

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pand data flows on a diagram5.155.15

Common DFD errors

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Data Flow Diagramming Rules

ProcessA. No process can have only

outputs (a miracle)

Data StoreD. Data cannot be moved

from one store to anotheroutputs (a miracle)

B. No process can have only inputs (black hole)

from one store to another

E. Data cannot move from an outside source to a data

C. A process has a verb phrase label

store

F. Data cannot move directly from a data store to a datafrom a data store to a data sink

G. Data store has a noun h l b lphrase label

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5.175.17

Data Flow Diagramming Rules

Source/SinkH. Data cannot move directly

from a source to a sink

Data FlowJ. A data flow has only one

direction of flow betweenfrom a source to a sink

I. A source/sink has a noun phrase label

direction of flow between symbols

K. A fork means that exactly the same data go from a common location to two or more processes, data p ,stores or sources/sinks

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5.185.18

Data Flow Diagramming Rules

Data Flow (Continued)L. A join means that exactly the same data come from

any two or more different processes, data stores or sources/sinks to a common location

M A d t fl t di tl b k t thM. A data flow cannot go directly back to the same process it leaves

N A data flow to a data store means updateN. A data flow to a data store means update

O. A data flow from a data store means retrieve or use

P A data flow has a noun phrase labelP. A data flow has a noun phrase label

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5.195.19

illegal Data Flows

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Logic Modeling

Data flow diagrams do not show the logic inside the processes

Logic modeling involves representing internal structure and functionality of processes depicted yon a DFD

Two methodsTwo methodsStructured English

Decision TablesDecision Tables

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5.215.21

Modeling Logic with Structured English

Modified form of English used to specify the logic of information processes

Uses a subset of EnglishAction verbs

Noun phrases

No adjectives or adverbsj

No specific standards

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5.225.22

Structured English Example

START

Initialize storageTOTAL.SALES, TOT.COM = 0

Process sales dataDO WHILE (more records)DO WHILE (more records)

PERFORM READ DATAPERFORM PROCESS DATAPERFORM PRINT DATA

END DO

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Policies and Decision Tables

Policy – a set of rules that govern show a process is to be completed.

Decision table – a tabular form of presentation that specifies a set of conditions and their corresponding actions.

As required to implement a policy.

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A Simple Decision Table

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Data Dictionary

Written description of the data contained in the database

First ones maintained in hardcopy form

Most are now maintained on a computerMost are now maintained on a computer

Data flow dictionary entry describes data flows on DFDon DFD

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Data Flow Dictionary Entryy y

Data flow name: Sales Order

Description: The documents that are pfilled out by customers to identify

the products, and the quantities of each, that theyquantities of each, that they will wish to purchase.

From: 1 Open mailFrom: 1. Open mail

To: 2. Enter sales order informationinformation

Data structures: Sales order record

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Comments:

Data Store Dictionary Entry

Data store name: Sales order form

Description: The history file of sales order forms, p yafter the data has been entered into the sales

commission system.

Data structures: Sales order record

Volume: Approximately 140 per dayVolume: Approximately 140 per day

Activity:

Access: Order department personnel

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Comments:

A DFD example

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