data flow diagrams a structured analysis technique that employs a set of visual representations of...

Data Flow Diagrams

A structured analysis technique that employs a set of visual representations of the data that moves through the organization, the paths through which the data moves, and the processes that produce, use, and transform data.

2

Why Data Flow Diagrams?

• Can diagram the organization or the system

• Can diagram the current or proposed situation

• Can facilitate analysis or design

• Provides a good bridge from analysis to design

• Facilitates communication with the user at all stages

Types of DFDs

• Current - how data flows now

• Proposed - how we’d like it to flow

• Logical - the “essence” of a process

• Physical - the implementation of a process

• Partitioned physical - system architecture or high-level design

Levels of Detail

• Context level diagram - shows just the inputs and outputs of the system

• Level 0 diagram - decomposes the process into the major subprocesses and identifies what data flows between them

• Child diagrams - increasing levels of detail

• Primitive diagrams - lowest level of decomposition

Four Basic Symbols

Source/Sink

Data Flow

#

Process# Data Store

Context Level Diagram

• Just one process

• All sources and sinks that provide data to or receive data from the process

• Major data flows between the process and all sources/sinks

• No data stores

Running Example

Course Registration: Context level Diagram

0

CourseRegistration

System

Student

Registrar

Professor

Class Request

Payment

Receipt

Student Schedule

Class roster

Enrollmentstatistics

Modeling Dilemma: Scope

• Deciding whether an entity is an external source/sink or an integral part of the system

• E.g. users of the system, managers who oversee the process

• Does the entity simply provide or receive information, or do they perform some part of the process?

Level 0 Diagram

• Process is “exploded”

• Sources, sinks, and data flows repeated from context diagram

• Process broken down into subprocesses, numbered sequentially

• Lower-level data flows and data stores added

Running Example

Course Registration: Current Logical Level 0 Diagram

Student RegistrarProfessor

1.0

RegisterStudent for

Course

D1 Student Class Records

D2 Student Payments

2.0

CollectStudent Fee

Payment

3.0

ProduceStudent

Schedule

4.0

ProduceClassRoster

5.0

ProduceEnrollment

Report

PaymentInformation

Student andCourse Data

StudentClass Record

Student Class Record Student Class Record

Student Class Record

Student Schedule Class RosterEnrollment

Report

StudentClass Request

Receipt

Payment

Child Diagrams

• “Explode” one process in level 0 diagram• Break down into lower-level processes, using

numbering scheme• Must include all data flow into and out of

“parent” process in level 0 diagram• Don’t include sources and sinks• May add lower-level data flows and data

stores

Running Example

Course Registration: Current Logical Child Diagram

1.2

Checkfor

Availability

1.1

CheckPrerequisites

Met

1.3

EnrollStudentin Class

D1 Student Class RecordsD5 Course CatalogueD4 Student Transcripts

D3 Semester Schedule

Class Request Valid ClassRequest

Feasible ClassRequest

Available Seats

Available Seats

StudentRecord

Course RecordStudent

and CourseData

Error

Error

Physical DFDs

• Model the implementation of the system

• Start with a set of child diagrams or with level 0 diagram

• Add implementation details– indicate manual vs. automated processes– describe form of data stores and data flows– extra processes for maintaining data

Running Example

Course Registration: Current Physical Child Diagram

1.2

Checkfor

Availability(myUMBC)

1.1

CheckPrerequisites

Met(manual)

1.3


(STARS)

D1 Semester Enrollment DBD5 Course Catalogue (text)D4 Department Student File

D3 Semester Schedule DB

Class Request AdvisementAuthorization

Feasible ClassRequest

Available Seats

Available Seats

Studentand Course

Data

Student Notified(verbally)

UnavailabilityMessage

StudentFile

Course Description

Running Example

Course Registration: Proposed Physical Child Diagram

1.2

Checkfor

Availability(automated)

1.1

CheckPrerequisites

Met(automated)

1.3


(automated)

D1 Semester Enrollment DBD5 Course Catalogue DBD4 Registrar’s Student DB


Class Request AuthorizedClass Request

Valid ClassRequest

Available Seats

Available Seats

Studentand Course

Data

Student Notified(email)

StudentEmailed

StudentRecord

Course Record

Partitioning a physical DFD

• Part of system design

• System architecture– high-level design– overall shape of system– some standard architectures

• Decide what processes should be grouped together in the system components

Running Example

Course Registration: Physical diagram (partitioned)

1.2

Checkfor

Availability(automated)

1.1

CheckPrerequisites

Met(automated)

1.3


(automated)

D1 Semester Enrollment DBD5 Course Catalogue DBD4 Registrar’s Student DB


Class Request AuthorizedClass Request

Valid ClassRequest

Available Seats

Available Seats

Studentand Course

Data

Student Notified(email)

StudentEmailed

StudentRecord

Course Record

Balancing

• Most important rule in data flow diagramming

• Every child diagram must include the same inputs and outputs as the process it represents in its parent diagram

• Also applies to the level 0 diagram

• Checking for balancing is a good way to find errors and omissions in your DFDs

1.0

GetCustomerAddress

CustomerInformation Customer

Address

1.2

ExtractCustomerAddress

1.1

LookupCustomer

Entry

CustomerInformation Customer

RecordCustomerAddress

1.2

ExtractCustomerAddress

1.1

LookupCustomer

Entry

CustomerInformation

CustomerRecord

CustomerZip Code

DirectoryName

DirectoryName

Balancing Exceptions

• A data flow at one level may be decomposed at a lower level

• On low-level DFDs, new data flows can be added to represent exceptional situations

• All data coming into and out of a process must be accounted for

1.0

GetCustomerAddress

CustomerInformation

CustomerAddress

1.2

LookupCustomerAddress

1.1

GetCustomer

Phone

1.3

RequestCustomerAddress

CustomerPhone

CustomerAddress

CustomerPhone

CustomerAddress

1.0

GetCustomerAddress

CustomerInformation

CustomerAddress

1.2

LookupCustomerAddress

1.1

GetCustomer

Phone

1.3

RequestCustomerAddress

CustomerPhone

CustomerAddress

CustomerPhone

CustomerAddress

Invalid PhoneNumber Message

Another Example

Perfect Pizza: Context Level Diagram

0

CustomerOrder

System

Customer

Cook

Management

Phone Number

Customer Order

Customer Info

DeliveryInformation

WeeklyReport

Cook OrderDeliveryPerson

Another Example

Perfect Pizza: Current Logical Level 0 Diagram

1.0Find

CustomerRecord

7.0Print

WeeklyTotals

6.0SendOrder

to Cook

5.0Add

CustomerRecord

2.0Take

CustomerOrder

3.0Print

DeliveryOrder

Customer

CustomerInfo

PhoneNumber

Customer Order

D1 Customer Master

CustomerRecord

CustomerRecord

CustomerInformation

D2 Customer History

D3 Sales Records

OrderInformation

OrderInformation

CustomerHistory

DeliveryInformation

CustomerCustomerOrder

Cook

CookOrder

Management

Sales Info

Weekly Report

DiscountInfo

DeliveryPerson

Another Example

Perfect Pizza: Current Logical Child Diagram

3.1

DetermineCustomerDiscount

3.2

RecordDiscount

3.3

PrintDelivery

Instructions

OrderInformation

DiscountAmount

DeliveryInformation

D2 Customer History

D3 Sales Records

CustomerHistory

DiscountInformation

CustomerInformation

Another Example

Perfect Pizza: Current Logical Child Diagram

5.1

RecordCustomer

Information

5.2

StoreCustomer

Record

D1 Customer Master

Customer Information RawCustomer

Information

CustomerRecord

Another Example

Perfect Pizza: Physical Child Diagram

5.3Clerk

VisuallyConfirmsCust. Info.

5.1Clerk Types

CustomerInformation

5.2System

ValidatesCustomer

Information

5.4Format

CustomerRecord

PhonedCustomer

InformationRecordedCustomer

Information

Valid CustomerInformation

SyntaxErrors

CancelledTransaction

New CustomerInformationD1 Customer DB

CustomerRecord

PhoneNumber

Another Example

Perfect Pizza: Current Physical Level 0 Diagram

1.0Clerk FindsCustomer

Row

7.0Mgr Prints

WeeklyTotals(batch)

6.0Clerk Sends

Orderto Cook(paper)

5.0Clerk AddsCustomer

Row

2.0Clerk TakesCustomer

Order(by phone)

3.0System Prints

DeliveryOrder

Customer

PhonedCustomer

Info

PhoneNumber

PhonedCustomer Order

D1Customer Spreadsheet

CustomerRecord

CustomerRecord

CustomerInformation

D2 Customer History DB

D3 Sales Records File

Copy ofOrder Slip

Customer& Order

Info

CustomerHistoryRecord

DeliveryPrintout

Customer

CookCopy of

order slipManagement

Copies ofOrder Slips

Weekly ReportPhone #

Cust.Info.

DeliveryPerson

8.0Mgr Updates

CustomerHistory

(nightly)Copies of

Order Slips& Del. Printouts


PhonedCustomer

Order

Another Example

Perfect Pizza: Proposed Physical Level 0 Diagram

1.0System Finds

CustomerRecord

7.0System Prints

WeeklyTotals(batch)


Record

2.0Clerk Enters

CustomerOrder

(by phone)

3.0System Prints

DeliveryOrder

Customer

PhonedCustomer

Info

PhoneNumber


D1 Customer DB

CustomerRecord

CustomerRecord

CustomerInformation


D3 Sales DB

OrderInfo

OrderInfo


DeliveryPrintout

Cook Management

SalesRecords


Cust.Info.

DeliveryPerson

D3 Sales DBOrderInfo

DiscountInfo

Another Example

Perfect Pizza: Partitioned Physical Level 0 Diagram

1.0System Finds

CustomerRecord

7.0System Prints

WeeklyTotals(batch)


Record

2.0Clerk Enters

CustomerOrder

(by phone)

3.0System Prints

DeliveryOrder

Customer

PhonedCustomer

Info

PhoneNumber


D1 Customer DB

CustomerRecord

CustomerRecord

CustomerInformation


D3 Sales DB

OrderInfo

OrderInfo


DeliveryPrintout

Cook Management

SalesRecords


Cust.Info.

DeliveryPerson

D3 Sales DBOrderInfo

DiscountInfo

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