2-SE1 The Engineering Design of Systems: Models and Methods Buede Chapter 2 – Slide 5+ Overview of...

2-SE 1

The Engineering Design of Systems: Models and

Methods

Buede Chapter 2 – Slide 5+

Overview of the Systems Engineering Design Process

Buede Chapter 3 – Slide 38+

Modeling and Process Modeling

Traditional “System” Model at Start of High-level Design

• Step 1 – It’s a “cloud”

– Which does stuff for external users or systems:

– We talk about its role in regard to that outside world.

– What does it “do”?

2-SE 2

Then we carve-up the cloud

• What top-down design would make all that happen?

• How would those parts of the cloud have to interact?

2-SE 3

At some point, bottom-up design starts to seep in

• Then it takes over for real, saying what the components “have to be”…

2-SE 4

2-SE 5

Buede’s Big Picture

OperationalConcept

Stakeholders

Life-CyclePhase

ObjectivesHierarchy

Stakeholders

OriginatingRequirements

Life-CyclePhase

ExternalSystemsDiagramInputs &

Outputs

Inputs &Outputs

CompleteInputs &Outputs

Objectives

Validation &AcceptanceTest Scenarios

FunctionalArchitecture

PhysicalArchitecture

OperationalArchitecture

StateTransitionDiagram

DerivedRequirementsand Flowdown

Risk Analysis and

Documentation

Interfaces

2-SE 6

Ch. 2 - Key Systems Terms see figure 2.1

• System – set of components acting together (SOI – system of interest)

• System’s External systems – set of entities that interact via the external interfaces.

• System’s Context – set of entities that can impact but not be impacted by the system.

2-SE 8

System/External Systems/Context

System

External Systems

Context

are impacted by “System”

impacts, but not impacted by, “System”

External Systems Diagram Captures this Viewpoint

2-SE 9

Some Key Concepts

• System’s inputs come from external systems or context.

• All of system’s outputs flow to external systems.

Play a role in

establishing requirement

s

2-SE 10

Buede’s Observation

•The design process, as presented, is not a ‘formal’ process.– Success and

correctness cannot be proven or guaranteed.

Understand UserRequirements, Develop

System Concept andValidation Plan

Develop SystemPerformance Specification

and SystemValidation Plan

Expand PerformanceSpecifications into CI

“Design - to” Specificationsand CI Verification Plan

Evolve “Design - to”Specifications into

“Build - to” Documentationand Inspection Plan

Fab , Assemble andCode to “Build - to”

Documentation

Inspect“Build - to”

Documentation

Assemble CIs andPerform CI Verification

to CI “Design - to”Specifications

Integrate System andPerform SystemVerification to

Performance Specifications

Demonstrate andValidate System to

User Validation Plan

. . .

Time










Documentation


Documentation







. . .

Time

Design Engineering

Systems Engineering

2-SE 11

Six Main Steps of Design Process

1. Define the system level design problem.

a. Develop operational concept

b. Define system boundary and external systems diagram

c. Develop system objectives hierarchy

d. Develop, analyze, and refine requirements

e. Ensure requirements feasibility

f. Define test system requirements

g. Obtain approval of system documentation

As in, a short “problem statement”!

2-SE 12

Six Main Steps of Design Process

1. Define the system level design problem.

2. Develop the system functional architecture

3. Develop the system physical architecture

4. Develop the system operational architecture

5. Develop the interface architecture

6. Define the qualification system

This may appear to be a linear, sequential process…..

• But it’s not.

• Consider qualification early on, look ahead, look back, revise and refine.

2-SE 14

2-SE 15

More Concepts and Terminology (Section 2.3)

• ‘Operational Concept’

1. Vision of the system – general terms

2. Mission requirements, How used

3. Set of operating scenarios

2-SE 16

Elevator Operational Concept

1. Vision• Product and market background

2. Mission• Performance objectives

3. Operational Phase Scenarios• Text and ‘input/output trace’

summaries of scenarios

See hand-out

2-SE 17

Operating Scenario

• In Systematica– ‘Functional Interactions’

between systems.– A collection of

‘Interactions’ becomes a ‘Feature’.

– ‘Interactions’ happen in a state of the State Diagram.

Passenger Elevator

Up Service Request

Feedback that request was received

Feedback that car is on the way

Entry Opportunity

Floor Request

Feedback that request was received

Feedback that door is closing

Feedback about floor where stopped

Feedback that door is opening

Exit Opportunity

Feedback that door is opening

Input/Output Trace See Elevator Handout

2-SE 18

External Systems Diagram (ESD)

• Defines the ‘boundary’ of our system

• Where it starts and ends

• Consistent with Operational Concept

• Developed from the Operating Scenarios• Figure 2.2 – Elevator Example.

Sometimes called : Domain or Context diagram

2-SE 19

Elevator System ESD 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. 1

xElevator Case StudyDennis Buede

George MasonUniv.

09/27/1999

A-1

ProvideElevatorServices

A0

Comm. about Emergency,Passenger WeightCharacteristics,Sensed PassengerHeat Loss/Gain

Relayed Info about Emergency,Electric Power,Sensed Building Heat

Maint. Action,Diagnosis Signals,Repairs,Test Signals

Up Service Request,Floor Request,

Request to Extend Entry support

Fire Alarm Signal

Signal for Partial Maint. Mode,Signal for Full Op'g Mode

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

Malfunction SignalElevator Entry/Exit Opportunity,Information about Emergency,Elevator Heat Loss/Gain

RequestElevatorServices

A-11

MaintainElevator

Operations

A-13

ProvideStructuralSupport

A-14

Passengers' Needs

EmergencyMessages

EmergencyComm'n

Passengers Elevator System Maintenance Personnel Building

RepairParts

External Systems Diagram for Operational Phase

MaintenanceQuality Standards

GovernmentRegulations

Diagnosis Response,Test Response

ElectricalPower

RelayedEmer.Comm.

Info. aboutEmergency

Fire Alarm

Figure 2.3 – IDEF0 modeling

2-SE 20

Elevator Example Comments

• Two slightly different versions of it

– One in book & author’s PPT slides.

– One better and more detailed provided as a case study.

2-SE 21

External Systems & Context

System

External Systems

Context



Figure 2.1

2-SE 22

Create a Graphical Model for the ESD

• Integrated Definition for Functional Modeling – IDEF0.

• Detailed in Chapter 3.

– Boxes – functions, verb phrases

– ICOM – inputs, controls, output, mechanisms.

2-SE 23

Objectives Hierarchy

• Hierarchical representation of major performance, cost, and schedule attributes.

• Define stakeholder satisfaction.

2-SE 24

Requirements

• Define operational requirements – what we want the system to accept, do, and be.

• Several approaches to Requirements – Ch. 6

• “Old school” - Carefully constructed written statements.

• “Agile” – User stories, etc.

25

Levels of Requirements

Mission Requirements

Originating Requirements

System Requirements

Component Requirements

CI Requirements

Derived Requirements

Figure 6.1

Stakeholder Requirements

Use our engineering skills and talents to create, develop, design

“CI’s” are “System Configuration Items”

2-SE 26

Two levels of Requirements:Originating and System

• Originating

• (Shareholder)

– Stakeholders agree with these.

– Written in English.

• System

– Translation of originating into engineering terms.

– Weight, speed, distance.

2-SE 27

Four Categories of Requirements

• Input/Output

– Inputs, outputs, external interfaces, functional requirements.

– Really important for describing system behavior

• Technology and System Wide

– ‘Technology’ in the system

– ‘Ilities’ of the system

– Cost, schedule

2-SE 28

Categories of Requirements

• Trade-off Requirements– Performance, cost

– Cost/performance

– Algorithms to enable

• System Qualification– How to obtain test data

– Data used for design = real system

– Data used for real system = originating reqs.

– Data used for real system = stakeholders wants

2-SE 29

Function• Process that changes inputs into

outputs.

• Describes ‘what’ not ‘how’

• Top level – single function

• Sub-functions below

VerbNoun Noun

2-SE 30

Interfaces are critical

• Connection resource

• ‘Hook together’ components and external systems.

• Interfaces have inputs, outputs, perform functions.

• May be software, hardware, mechanical, electrical, etc.

2-SE 31

QualificationVerify/Validate/Accept

• Qualification – means ‘test’ and an umbrella term for V&V

• Verification – was system built right.

• Validation – was right system built (meets scenarios and requirements).

• Acceptance – stakeholders feel system meets their needs, acceptable.










Documentation


Documentation







Decom

position

and

Definition

. . .

Time










Documentation


Documentation



Integrate System and

Perform SystemVerification to




Decom

position

and

Definition

. . .

Time

Inte

grat

ion

and

Qua

lific

atio

n

Design Engineering

Systems Engineering

2-SE 32

The Big Picture

OperationalConcept

Stakeholders

Life-CyclePhase

ObjectivesHierarchy

Stakeholders

OriginatingRequirements

Life-CyclePhase

ExternalSystemsDiagramInputs &

Outputs

Inputs &Outputs

CompleteInputs &Outputs

Objectives

Validation &AcceptanceTest Scenarios

FunctionalArchitecture

PhysicalArchitecture

OperationalArchitecture

StateTransitionDiagram

DerivedRequirementsand Flowdown

Risk Analysis and

Documentation

Interfaces

2-SE 33

The Big Picture

2-SE 34

This seems complicated – what about software tools ?

• Buede suggests CORE Software

• Many systems engineering software tools available.

• Issues – learning curve, power, detail, flexibility, terminology, automation, etc.

Let’s keep it simple

• Microsoft Word, Excel, Visio

2-SE 35

2-SE 36

Visio or similar software?

• Multipurpose drawing/flowcharting package.

• Shape oriented concept.

• A good tool for engineers.

• You should be able to get Visio (for MS) on Rose’s Banner site (= MSDNAA).

2-SE 37

Visio Demonstration?

• Overview of basic features.

• Shape stencils

• Drag and drop shapes

• Edit shape properties

• Text

• Tools : Alignment, Group, Rotate, etc.

• Pages

2-SE 38

Ch. 3 – Modeling and IDEF0

• Models are abstractions of reality….

• Modeling languages –

– Semantics – symbols, signs.

– Syntax – rules for combining symbols.

• Process models – input/function/output.

• IDEF0 and others in Ch.12.

2-SE 39

External Systems & Context

System

External Systems

Context



Figure 2.1

2-SE 40

MBSE

• We will be learning ‘Model Based Systems Engineering’ (MBSE)

• Building graphical models to depict system structure and behavior.

• Far less dependent on volumes of written requirements.

2-SE 41

Pattern Based Systems Engineering - PBSE

2-SE 42

Models

• Models are an abstraction….

• The essence of a model is the set of questions that the model can answer for us.

2-SE 43

The Truth About Models

• Models are –

– Incomplete,

– Inaccurate,

– Simplified,

– Etc.

All models are wrong, but some are useful. (George Box)

Software’s love/hate thing with models

• To agile people – just one more thing not to do if you don’t have to

• To organizations with a well-defined way to convert requirements to models, etc. – the only way to go! (E.g., the Rational process.)

• To organizations without that, doing one more routine project – something we wish we could try!

• To organizations who are now facing a new kind of project – a dream / something new to try, if we have time!

2-SE 44

2-SE 45

Types of Models

• Physical – Mock-ups,

– Scale models,

– Prototypes,

– Breadboards.

• Questions: how much, visualization, scenario testing.

2-SE 46

Types of Models - 2

• Quantitative

– Analytic,

– Empirical,

– Simulation

– Static/dynamic, deterministic/stochastic.

• Questions: How much, often, good, etc.

2-SE 47

Types of Models - 3

• Qualitative

– Symbolic,

– Text,

– Graphic

• Questions : what needs to be done, what order, etc.

2-SE 48

Types of Models - 4

• Mental

– Abstractions of thought.

– Highly useful, but hard to communicate.

– We use in interaction design –

• “What’s the user think this is?”

2-SE 49

Potential Uses of Models

1. Create, specify, communicate, and test a shared vision.

2. Estimation and prediction of qualitative measures.

3. Selection of one option over another.

Buede text emphasizes qualitative modeling.

2-SE 50

The SE Design Strategy

• The ‘Onion’ concept

• Primarily top-down

• High level of Abstraction

– Proceeding to

• More and more detail and definition

• Decomposition or modular approach

2-SE 51

The SE Design Strategy

2-SE 52

IDEF0 Modeling

• Section 3.3 – visit www.idef.com

– Lots of examples

• Function box – Verb phrase, number.

• Flow of material or data or information.

• A-0 is the ‘ESD/context diagram’.

• A0 is the top level function.

• Decomposition

http://www.idef.com/

2-SE 53

IDEF0 Page StructurePage #’s Function #’s A-1

A-0

A0

A1, A3

A33

A0

A1 A2 A3

A11 A12 A13 A31 A32 A33 A34

A331 A332 A333 A335A334

A-0 A-12A-11 A-13

Page Number(s) Page Content

A - 1 Ancestor or external system diagram

A - 0 Context or system function diagram (contains A0)

A0 Level 0 diagram with first tier functions specified

A1, A2, ... Level 1 diagrams with second tier functions specified

A11, A12, ..., A21, ...

Level 2 diagrams with third tier functions specified

... …

Figure 3.5; Table 3.2

Wasson Decomposition Notations

2-SE 54

2-SE 55

The IDEF0 Model

• Answers definitive questions about the transformation of inputs into outputs by the system

• Establishes the boundary of the system on the context page.

• Has one viewpoint; the viewpoint is the vantage or perspective from which the system is observed.

• Can create a coordinated set of diagrams, using both a graphical language and natural language.

2-SE 56

IDEF0 – 2

• ICOM – inputs, controls, outputs, mechanisms.

• Not a sequence of activities – (a functional model, not a behavioral one).

USED AT: CONTEXT:


AUTHOR:PROJECT:

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

DATE:REV:

WORKING

DRAFT

RECOMMENDED

PUBLICATION

READER DATE

P.

PROVIDE ELEVATOR SERVICES

A0

PassengerCharacteristics

Electric Power& EmergencyCommunication Response

Service, Tests& Repairs

Request forEmergencySupport &EmerencyMessage

Request forFloor & Exit Support

Request forElevator Service &Entry support

StructuralSupport,Alarm Signals& BuildingEnvironment

ModifiedElevatorConfiguration& ExpectedUsage Patterns

PassengerEnvironment

Acknowledgmentthat Request WasRecieved & StatusInformation

Diagnostic &Status Messages

ElevatorEntry/ExitOpportunity

EmergencySupport

EmergencyCommunication

Elevator System

Top

2


George Mason Univ.

05/24/99

Provide Elevator ServicesA-0

I O

C

M

2-SE 57

IDEF0 Rules & Guidelines

• Rules– Conservation of inputs, controls, outputs &

mechanisms

– Every function has a control and output

• Input vs. Control – which is it?– Inputs – transformed or consumed.

– Controls – information, conditions, or instructions that guide the functional process.

2-SE 58

IDEF0 Rules & Guidelines

• Guidelines– 3 to 6 functions per page arranged

diagonally

– Control-oriented functions placed at top left

– Major output functions placed on bottom right

– Arcs & functions are decomposable

– Feedback is defined by arcs moving from bottom right to top left

2-SE 60

Feedback Semantics of Functions

Mechanism Feedback

Input Feedback

down & under

label

Control Feedbackup & over

label

down & under label

Figure 3.4

2-SE 61

IDEF0 Functional

Decomposition

Transform I1.1into O1 & O2.1

as determined byC1 & C2

using M1.1

Transform O2.1 & I1.2into O2.2

as determined byC2, C3 & O1using M1.2

Transform I2into O3

as determined byC2 & C3

using M1.3

I1

I2

C1 C2 C3

O1

O2

O3

M1

M1.1

M1.2

M1.3

O2.1

O2.2I1.2

I1.1

A1

A2

A3

Transform I1 & I2into O1, O2 & O3as determined by

C1, C2 & C3using M1

I1

I2

C1 C2 C3

O1

O2

O3

M1

A0

Figure 3.6

2-SE 62

Elevator External Systems Diagram USED AT: CONTEXT:


AUTHOR:PROJECT:

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

DATE:REV:

WORKING

DRAFT


READER DATE

P. 1


George MasonUniv.

09/27/1999

A-1

ProvideElevatorServices

A0

Comm. about Emergency,Passenger WeightCharacteristics,Sensed PassengerHeat Loss/Gain





Fire Alarm Signal


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

Malfunction SignalElevator Entry/Exit Opportunity,Information about Emergency,Elevator Heat Loss/Gain

RequestElevatorServices

A-11

MaintainElevator

Operations

A-13

ProvideStructuralSupport

A-14

Passengers' Needs

EmergencyMessages

EmergencyComm'n

Passengers Elevator System Maintenance Personnel Building

RepairParts

External Systems Diagram for Operational Phase

MaintenanceQuality Standards

GovernmentRegulations


ElectricalPower

RelayedEmer.Comm.

Info. aboutEmergency

Fire Alarm

From the ElevatorCase Write Up Slightly different from book figures….

2-SE 63

Elevator System Function

Top level system function

USED AT: CONTEXT:


AUTHOR:PROJECT:

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

DATE:REV:

WORKING

DRAFT


READER DATE

P.

Top

2


George MasonUniv.

09/27/1999

Provide Elevator ServicesA-0

PROVIDEELEVATORSERVICES

A0



PURPOSE: To define boundary and architectures for the Operational Phase of the Elevator SystemVIEWPOINT: Up & Down, Ltd. Systems Engineering Team

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



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

MalfunctionSignal

Elevator Entry/Exit Opportunity,

Information about Emergency,Elevator Heat

Loss/Gain

EmergencyComm'n


Fire Alarm Signal


Elevator System

2-SE 64

Elevator Functional Decomposition

First level decomposition

USED AT: CONTEXT:


AUTHOR:PROJECT:

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

DATE:REV:

WORKING

DRAFT


READER DATE

P.

A-0

3


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




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

Maint. Action,Diagnosis Signals,

Repairs,Test Signals


MalfunctionSignal

Feedback: Service Request Recieved,




Fire Alarm;Entry/Exit Opp'y Ending 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


Up Service Request,Floor Request

Feedback: Service Request Recieved,




Fire Alarm

Entry/Exit Opp'y Ending Signal;


OperatingMode

Diagnosis Signals,Maint. Action,Repairs,Test Signals

2-SE 65

Getting the ESD Right

• The ESD must capture the fundamental functional activity of the system being modeled.

• It’s how “the system as a cloud” interacts with the external world.

2-SE 66

Problems• Develop an external systems diagram for an

ATM machine (scenario on next page)

• Class exercise? Or after class…– Develop a scenario or two and an ‘external systems

diagram’ for a common system.

– Develop a scenario or two and an ‘external systems diagram’ for your design problem.

2-SE 67

W/D Activity

Request forAccount Type

Account Type

Request for Amount

General ID

Request forUnique ID

Unique ID

Request for Activity

Customer BankComputer

ATM

Transaction

Request for Fmax

Customer Scenario #2a

Trans Amount (Creq)

Fmax

Receipt

Main Menu

Cust Cash

2-SE1 The Engineering Design of Systems: Models and Methods Buede Chapter 2 – Slide 5+ Overview of...

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