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The Engineering Design of Systems: Models and Methods. Chapter 2 Overview of the Systems Engineering Design Process Chapter 3 Modeling and Process Modeling. The Big Picture. Functional Architecture. Operational Architecture. Physical Architecture. State Transition Diagram. Derived

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the engineering design of systems models and methods

The Engineering Design of Systems: Models and Methods

Chapter 2

Overview of the Systems Engineering Design Process

Chapter 3

Modeling and Process Modeling

2-SE

the big picture
The Big Picture

Functional

Architecture

Operational

Architecture

Physical

Architecture

State

Transition

Diagram

Derived

Requirements

and Flowdown

Interfaces

Risk Analysis

and

Documentation

2-SE

ch 2 key systems terms see figure 2 1
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

system external systems context
System/External Systems/Context

External Systems Diagram

Captures this Viewpoint

2-SE

some key concepts
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 requirements

2-SE

buede s observation
Buede’s Observation
  • The design process, as presented, is not a ‘formal’ process.
    • Success and correctness cannot be proven or guaranteed.

2-SE

six main steps of design process
Six Main Steps of Design Process
  • Define the system level design problem.
    • Develop operational concept
    • Define system boundary and external systems diagram
    • Develop system objectives hierarchy
    • Develop, analyze, and refine requirements
    • Ensure requirements feasibility
    • Define test system requirements
    • Obtain approval of system documentation

2-SE

six main steps of design process1
Six Main Steps of Design Process
  • Define the system level design problem.
  • Develop the system functional architecture
  • Develop the system physical architecture
  • Develop the system operational architecture
  • Develop the interface architecture
  • Define the qualification system

2-SE

this may appear to be a linear sequential process
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

more concepts and terminology section 2 3
More Concepts and Terminology (Section 2.3)
  • ‘Operational Concept’
    • Vision of the system – general terms
    • Mission requirements, How used
    • Set of operating scenarios

2-SE

elevator operational concept
Elevator Operational Concept

See hand-out

  • Vision
    • Product and market background
  • Mission
    • Performance objectives
  • Operational Phase Scenarios
    • Text and ‘input/output trace’ summaries of scenarios

2-SE

operating scenario
Operating Scenario
  • In Systematica
    • ‘Functional Interactions’ between systems.
    • A collection of ‘Interactions’ becomes a ‘Feature’.
    • ‘Interactions’ happen in a state of the State Diagram.

See Elevator Handout

Input/Output Trace

2-SE

external systems diagram esd
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

elevator system esd
Elevator System ESD

2-SE

Figure 2.3 – IDEF0 modeling

elevator example comments
Elevator Example Comments
  • Two slightly different versions of it
    • One in book & authors PPT slides.
    • One better and more detailed provided as a case study.

2-SE

create a graphical model for the esd
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

objectives hierarchy
Hierarchical representation of major performance, cost, and schedule attributes.

Define stakeholder satisfaction.

Objectives Hierarchy

2-SE

requirements
Requirements
  • Define operational requirements – what we want the system to accept, do, and be.
  • Several approaches to Requirements – Ch. 6
  • Carefully constructed written statements.

2-SE

levels of requirements
Levels of Requirements

Stakeholder

Requirements

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

Figure 6.1

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.

Two levels of Requirements:Originating and System

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four categories of requirements
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

categories of requirements
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

function

Verb

Noun

Noun

Function
  • Process that changes inputs into outputs.
  • Describes ‘what’ not ‘how’
  • Top level – single function
  • Sub-functions below

2-SE

interfaces are critical
Interfaces are critical
  • Connection resource
  • ‘Hook together’ components and external systems.
  • Interfaces have inputs, outputs, perform functions.
  • May be software, hardware, mechanical, electrical, etc.

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qualification verify validate accept
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.

2-SE

the big picture1
The Big Picture

Functional

Architecture

Operational

Architecture

Physical

Architecture

State

Transition

Diagram

Derived

Requirements

and Flowdown

Interfaces

Risk Analysis

and

Documentation

2-SE

this seems complicated what about software tools
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.

2-SE

let s keep it simple
Let’s keep it simple
  • Microsoft Word, Excel, Visio

2-SE

visio software
Visio Software
  • Multipurpose drawing/flowcharting package.
  • Now part of Microsoft.
  • Shape oriented concept.
  • A good tool for engineers.

2-SE

visio demonstration
Visio Demonstration?
  • Overview of basic features.
  • Shape stencils
  • Drag and drop shapes
  • Edit shape properties
  • Text
  • Tools : Alignment, Group, Rotate, etc.
  • Pages

2-SE

ch 3 modeling and idef0
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

slide36
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

models
Models
  • Models are an abstraction….
  • The essence of a model is the set of questions that the model can answer for us.

2-SE

the truth about models
The Truth About Models
  • Models are –
    • Incomplete,
    • Inaccurate,
    • Simplified,
    • Etc.

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

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software s love hate thing with models
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!

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types of models
Types of Models
  • Physical
    • Mock-ups,
    • Scale models,
    • Prototypes,
    • Breadboards.
  • Questions: how much, visualization, scenario testing.

2-SE

types of models 2
Types of Models - 2
  • Quantitative
    • Analytic,
    • Empirical,
    • Simulation
    • Static/dynamic, deterministic/stochastic.
  • Questions: How much, often, good, etc.

2-SE

types of models 3
Types of Models - 3
  • Qualitative
    • Symbolic,
    • Text,
    • Graphic
  • Questions : what needs to be done, what order, etc.

2-SE

types of models 4
Types of Models - 4
  • Mental
  • Abstractions of thought.
  • Highly useful, but hard to communicate.

2-SE

potential uses of models
Potential Uses of Models
  • Create, specify, communicate, and test a shared vision.
  • Estimation and prediction of qualitative measures.
  • Selection of one option over another.

Buede text emphasizes qualitative modeling.

2-SE

the se design strategy
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

idef0 modeling
IDEF0 Modeling
  • Section 3.3 – visit www.idef.com
  • 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

2-SE

idef0 page structure

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

...

IDEF0 Page Structure

2-SE

Figure 3.5; Table 3.2

the idef0 model
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

idef0 2
ICOM – inputs, controls, outputs, mechanisms.

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

IDEF0 – 2

C

O

I

M

2-SE

idef0 rules guidelines
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

idef0 rules guidelines1
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

elevator external systems diagram
Elevator External Systems Diagram

2-SE

From the Elevator

Case Write Up

Slightly different than book figures….

elevator system function
Elevator System Function

2-SE

Top level system function

elevator functional decomposition
Elevator Functional Decomposition

2-SE

First level decomposition

problems
Problems
  • Develop an external systems diagram for an ATM machine (scenario on next page)
  • Class Exercise.
    • Develop a scenario or two and an ‘external systems diagram’ for a common system.
  • Break into your project groups.
    • Develop a scenario or two and an ‘external systems diagram’ for your design problem.

2-SE

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