1

Week 7 - Systems Engineering and

Analysis

Buede Chapter 12 – Graphical Modeling

Techniques

Left – Systems engineers us a lot of graphical models which look like state diagrams. If you have to predict how the pieces of a large system will interact, you need help visualizing that. This one is a “generative model for how to create generative models.”

2

Wasson also talks about modeling

• Mostly scattered by topic – what you are modeling.

• E.g., Sec 15.2 – System behavioral response model

• Ch 17 – Use Cases & UML• Ch 20 – Modeling system and support

operations• Ch 51 – System modeling and

simulation

3

Data, Process, and Behavior Models

• Data Models – relationships among input and outputs.

• Process Models – define functional decomposition of the system function and flow of inputs and outputs for those functions.

• Behavior Models – define the control, activation, and termination of of system functions needed to meet performance requirements.

4

Modeling Approaches & Methods• Data Modeling

– Entity-relationship diagrams (ERDs)– Higraphs

• Process Modeling– Data flow diagrams (DFDs)– IDEF0– N2 charts

• Behavior Modeling– Function flow block diagrams (FFBDs)– Behavior diagrams (BDs)– State-transition diagrams (STDs)– Statecharts– Control flow diagrams (CFDs)– Petri nets (PNs)

• Object-oriented Modeling– Object modeling technique (OMT)– Real-time object-oriented modeling (ROOM)

Table 12.1

5

Data Flow Diagram Semantics

ProcessCustomerBanking

Transactions

ProcessCustomerBanking

Transactions

ProcessCustomerBanking

Transactions

These are three equally valid representations of a process. Note a process begins with a verb, just as functions or activitiesdo in IDEF0.

Customer Notice:Main Menu Selection

This is an example of a “dataflow”. Note, it is a nounphrase and attached to an arc.

Double-headedarcs signify dialogbetween functions

Figure 12.6

6

Context (External Systems) Diagram in DFD

CUSTOMERS

BANK SERVICEPERSONNEL

BANKCOMPUTER

CustomerNotices

(CN)CompletedTransaction

Prodcuts

CustomerInputs

SystemStatus Report

Account Transaction

DataCompletedTrans. Info.Bank's

Acct. Info

BankSupplies

Employee ID Info

PROVIDEAUTOMATED

TELLERMACHINE

SERVICES FORCUSTOMERS

Figure 12.9

7

N2 Charts – an SE favorite!Request for Elevator Service& Entry SupportRequest for EmergencySupportRequest for Floor & ExitSupport

Modified ElevatorConfiguration & ExpectedUssage Patterns

Electric Power & EmergencyCommunication ResponseGovernment RegulationsPassenger CharacteristicsStructural Support, AlarmSignals & BuildingEnvironment

Government RegulationsService, Tests & Repairs

Acknowledgment thatRequest Was Received &Status InformationEmergency Support

1.0

Accept Passenger Requests& Provide Feedback

·Digitized PassengerRequests

·Sensed Malfunctions

2.0

Control Elevator Cars

·Assignments for ElevatorCars

·Sensed Malfunctions

Elevator Entry OpportunityElevator Exit OpportunityPassenger Environment

·Elevator Position & Direction ·Elevator Position & Direction 3.0

Move Passengers BetweenFloors

·Sensed Malfunctions

Diagnostic & StatusMessages

·Temporary Modification toElevator Configuration

4.0

Enable Effective Maintenance& Servicing

Figure 12.10

8

Ref . AND AND

1. 1

Per f or m

Sy s t em Lev e l

Des ign Ac t iv it ies

1. 2

Pe r f or m

Subs y s t em

Lev e l Des ign . . .

1 . 3

Pe r f or m

Com ponent

Lev e l Des ign . . .

2

Pe r f or m

I n t egr at ion

Ac t iv it ies

Concurrent

Function Flow Block Diagrams

• Basic– Series– Concurrent– Selection– Multiple-exit function

• Enhanced– Iteration– Looping– Replication

Ref .

1

Per f or m Des ign

Ac t iv it ies

2

Per f or m

I n t egr at ion

Ac t iv it ies

Ref .

Series

Figure 12.11-12

9

Selection & Multiple-exit Functions, Iteration, Looping in FFBD

1

P e rfo rm D e s ig n

A c tiv itie s

IT ITL P L P

2 .3 .1

In s p e c t & T e s t

S u b s y s te m

O R

2 .3 .2

Id e n tify & F ix

C o rre c ta b le

D e fic ie n c ie s

O R

2 .3 .3

A s s e s s Im p a c t

o f

U n c o rre c ta b le ...

O R

2 .3 .4

R e d e s ig n

S u b s y s te m

2 .3 .5

M o d ify B a s e lin e

2 .3 .6

In te g ra te w ith

N e x t S u b s y s te m

2 .1

P e rfo rm

C o m p o n e n t

In te g ra tio n

c le a re d s u b s y s te m

d e fic ie n t s u b s y s te m

c o rre c ta b le d e f.

u n c o rre c ta b le d e f

a c c e p ta b le im p a c t

u n a c c e p ta b le im p a c t

if d e fic ie n c y is fix e d o r re d e s ig n e d

fo r e a c h s u b s y s te m

Figure 12.13

10

FFBD for Elevator

Ref . AND AND

1. 0

Ac c ept

Pas s enger

Reques t s & P. . .

2. 0

Cont r o l Elev at or

Car s

3. 0

M ov e

Pas s enger s

Bet ween Floor s

4. 0

Enab le Ef f ec t iv e

M ain t enanc e &

Ser v ic ing

Ref .

11

Elevator Functional Architecture USED AT: CONTEXT:

NODE: TITLE: NUMBER:

AUTHOR:PROJECT:

NOTES: 1 2 3 4 5 6 7 8 9 10

DATE:REV:

WORKING

DRAFT

RECOMMENDEDPUBLICATION

READER DATE

P.

A-0

3

xElevator Case StudyDennis Buede

George MasonUniv.

09/29/1999

PROVIDE ELEVATOR SERVICESA0

ACCEPTPASSENGERREQUESTS &

PROVIDEFEEDBACK

A1

CONTROLELEVATOR

CARSA2

MOVEPASSENGERS

BETWEENFLOORS

A3

ENABLEEFFECTIVE

MAINTENANCE& SERVICING

A4

DigitizedPassengerRequests

Assignmentsfor ElevatorCars

ElevatorPosition &Direction

Sensed Malfunctions,Diagnosis &Test Responses

TemporaryModificatin to

ElevatorConfiguration

ElectricPower

ElectricPower

Up Service Request,Floor Request,

Request to Extend Entry support

Relayed Info about Emergency,Electric Power,Sensed Building Heat

Comm. about Emergency,Passenger Weight Characteristics,Sensed Passenger Heat Loss/Gain

Maint. Action,Diagnosis Signals,

Repairs,Test Signals

Diagnosis Response,Test Response

MalfunctionSignal

Feedback: Service Request Recieved,

Floor Request Received, Car On Way,

Door Opening, Door Closing,

Floor Where Stopped, About Emergency;

Fire Alarm;Entry/Exit Opp'y Ending Signal;

Capacity Exceeded Signal

EmergencyComm'n

Elevator Entry/Exit Opportunity,

Information about Emergency,Elevator Heat

Loss/Gain

Fire Alarm SignalSignal for Partial Maint. Mode,Signal for Full Op'g Mode

Request to Extend Entry support

Up Service Request,Floor Request

Feedback: Service Request Recieved,

Floor Request Received, Car On Way,

Door Opening, Door Closing,

Floor Where Stopped, About Emergency;

Fire Alarm

Entry/Exit Opp'y Ending Signal;

Capacity Exceeded Signal

OperatingMode

Diagnosis Signals,Maint. Action,Repairs,Test Signals

12

Behavior Diagrams

@

@

&*

&*

@*

@*

UpdatePosition

UpdateDisplay

DetectionData

CurrentTrack

UpdatedTrack

UpdatedDisplay

Sequence

UpdatePosition

UpdateDisplay

UpdatedTrack

UpdatedDisplay

All tracks

@*

@*

All tracks

CurrentTrack

@*

@*

All tracks

DetectionData

@*

@*

All detections

Iteration

UpdatePosition

UpdateDisplay

DetectionData

CurrentTrack

DroppedTrack

UpdatedDisplay

Selection

+

UpdatedTrack

Track UpdateNo TrackUpdate

UpdatePosition

UpdateDisplay

DetectionData

CurrentTrack

UpdatedTrack

UpdatedDisplay

Concurrency

&

&

UpdatePosition

UpdateDisplay

DetectionData

CurrentTrack

UpdatedTrack

UpdatedDisplay

Replication

UpdatePosition

DetectionData

CurrentTrack

Looping

L

UpdatedTrack

RemainingDetections

G

DetectionsDepleted

Figure 12.14

13

Finite State Machines• Finite state machines:

discrete valued inputs, outputs and internal items– Sequential: past inputs

impact current outputs (e.g., state-transition diagram)

– Combinational: current outputs characterized only current inputs

• Continuous machines: continuous and discrete inputs, outputs and internal items

Continuous orAnalog Machines

CombinationalFSM

SequentialFSM

Finite StateM achines (FSMs)

M achines

Figure 12.16

14

State-transition Diagram for ATMIDLE

WAITING FOR CUSTOMER

IDENTIFICATION

WAITING FORCUSTOMER’S

ACCESS CODE

WAITING FORCUSTOMER’S

CHOICE

DEPOSIT WITHDRAWL TRANSFER ACCOUNTBALANCE

Cust. ID PresentedProcess ID for Validity

Cust. ID ReadCN:”Enter Access Code”

Access Code ValidatedCN:”Main Menu Choices”

Invalid Access CodeCN:”Please Re-enter”

3rd Invalid Access CodeCN:”Transaction Terminated”

Unread Cust. IDCN:”ID Unreadable”

Figure 12.17

Partially

Completed

Event

Output

15

State-transition Diagram for an Elevator

Elevator Idle,Door Open

Preparing ToMove Up

Preparing ToMove Down

ElevatorDoor Opening

ElevatorEnabling Entry/Exit

ElevatorMoving

ElevatorStopping

Elevator Starting

Checking NextDestination

Down RequestClose Door

Up RequestClose Door

Door ClosedUp Indicator

Door ClosedDown Indicator

Acceleration > 0Departed Floor

Near Requested FloorSlowing

Door OpenedDirection Indicator

Elevator StoppedDoor Activated

Pause Timer ElapsedDestination Query

Up RequestClose Door

Down RequestClose Door

No RequestMaintain Open Door

Figure 12.18

16

StatechartSUPERSYSTEM

HUMAN

AUTOMOBILE

b

b

CCSw

OFF

w( b)

b

m

X

NOT OFFb

bDRIVE DRIVE

ON OFF ARC LABEL DEFINITION

b turn on car

b hat turn off car

m accident occurs

w depress on/off button

External System Statechart For Cruise Control System

Figure 12.19

17

Statechart, cntd

Decomposition of the“Not Off” State

For Cruise Control System

NOT OFF

INDICATOR

DEAD

ALIVE

cd

SYSTEM STATUS

ON

STANDBYvr

fevs u

ARC LABEL DEFINITION

c circuit closed (good bulb or fuse)

d circuit open ( bad bulb or fuse)

e brake depressed

f clutch depressed

u wheel revolutions > 7920/ (pi*r) where r is the wheel radius in inches

vr push button to resume / set

vs push CCS button to standby

Figure 12.20

18

Statechart, cntd

Decomposition of the“Alive” State

for the Indicatorof Cruise Control System

ALIVE

BLINK

OFFONw

w wvr

f

e

vs

ARC LABEL DEFINITION

e brake depressed

f clutch depressed

vr push button to resume / set

vs push CCS button to standby

w depress on/off button

Figure 12.21

19

Statechart, cntdON

MAINTAIN

ACCELERATEDECELERATE

H

vr

k j i k

vd va

v v

hPULSE

h

vd

va

Decomposition of the“On” State

for the Indicatorof Cruise Control System

ARC LABEL DEFINITION

h non drive wheel RPM not equal to drive wheel RPM

h(hat) non drive wheel RPM equal to drive wheel RPM

i wheel RPM decrease from set speed

j wheel RPM increase from set speed

k wheel RPM match to set speed

v(hat) release the CCS button

va push CCS button to accelerate

vd push CCS button to decelerate

vr push button to resume / set

Figure 12.22

20

Statechart for Cruise Control SystemCCS

NOT OFF

INDICATOR

ALIVE

BLINK

ON

OFF

w

w

w

vr

f

e vs

DEADc

d

OFFw

w

b

m

ON

MAINTAIN

ACCELERATEDECELERATE

H

k jvd va

va

vd

i kvv

PULSE h

h

vr

STANDBY

MEMORYSET

MEMORYCLEAR

v

va

e f vsu

Figure 12.23

21

Object-oriented Modeling – our favorite in software?

• Object Modeling Technique (OMT)– Object model (ERD)– Dynamic model (STD & nested state diagrams)– Functional model (DFD)

• Real-time Object-oriented Modeling (ROOM)– Objects = Actors– Actors communicate via messages– ROOMcharts

• Combine functional and behavioral models• Generalization of Statecharts

• Unified Modeling Language (UML) (SysML)