©Sommerville 2000, Medvidovic 2006, Mejia 2009Systems EngineeringSlide 1 Systems Engineering l...

©Sommerville 2000, Medvidovic 2006, Mejia 2009 Systems Engineering Slide 1

Systems Engineering

Designing, implementing, deploying and operating systems which include hardware, software and people

Objectives• To explain why system software is affected by broader system

engineering issues• To introduce the concept of emergent system properties such as

reliability and security• To explain why the systems environment must be considered in

the system design process


What is a system? A purposeful collection of inter-related components

working together towards some common objective. A system may include software, mechanical,

electrical and electronic hardware and be operated by people.

System components are dependent on other system components

The properties and behaviour of system components are inextricably inter-mingled


Problems of systems engineering Large systems are usually designed to solve

‘nasty’ problems Systems engineering requires a great deal of

co-ordination across disciplines• Almost infinite possibilities for design trade-offs across

components

• Mutual distrust and lack of understanding across engineering disciplines

Systems must be designed to last many years in a changing environment


Software and systems engineering The proportion of software in systems is

increasing• Software-driven general purpose electronics is replacing

special-purpose systems

Problems of systems engineering are similar to problems of software engineering

Software is (unfortunately) seen as a problem in systems engineering• Many large system projects have been delayed because of

software problems


Emergent properties Properties of the system as a whole rather than

properties that can be derived from the properties of components

Emergent properties are a consequence of the relationships between system components

They can therefore only be assessed and measured once the components have been integrated into a system


Examples of emergent properties The overall shape and size of a physical system

• This depends on the composition of components.

The reliability of the system • This depends on the reliability of system components and the

relationships between the components.

The usability of a system • This is a complex property which is not simply dependent on the

system hardware and software but also depends on the system operators and the environment where it is used.


Types of emergent property Functional properties

• These appear when all the parts of a system work together to achieve some objective

• For example, a bicycle has the functional property of being a transportation device once it has been assembled from its components

Non-functional emergent properties• Examples are reliability, performance, safety, and security• These relate to the behaviour of the system in its operational

environment• They are often critical for computer-based systems as failure to

achieve some minimal defined level in these properties may make the system unusable.


Because of component inter-dependencies, faults can be propagated through the system

System failures often occur because of unforeseen inter-relationships between components• Honey-baked ham

It is probably impossible to anticipate all possible component relationships• Hardware• Software• Operator

System reliability


Reliability relationships Hardware failure can generate spurious signals

that are outside the range of inputs expected by the software

Software errors can cause alarms to be activated which cause operator stress and lead to operator errors

The environment in which a system is installed can affect its reliability• E.g., placement of a system intended to operate at room

temperature near an air conditioner


The ‘shall-not’ properties Properties such as performance and reliability

can be measured However, some properties are properties that the

system should not exhibit• Safety - the system should not behave in an unsafe way

• Security - the system should not permit unauthorised use

Measuring or assessing these properties is very hard• How do you know you are safe or secure?


System architecture modelling An architectural model presents an abstract view

of the sub-systems making up a system May include major information flows between

sub-systems Usually presented as a block diagram May identify different types of functional

component in the model


Functional system components Sensor components Actuator components Computation components Communication components Co-ordination components Interface components All are now usually software controlled


Hierarchies of Systems

Securitysystem

Heatingsystem

Lightingsystem

Powersystem

Wastesystem

Watersystem

Town

Street

Building


Intruder alarm system

Alarmcontroller

Voicesynthesizer

Movementsensors

Siren

Doorsensors

Telephonecaller

Externalcontrol centre


Component types in alarm system Sensor

• Movement sensor, Door sensor

Actuator• Siren

Communication• Telephone caller

Coordination• Alarm controller

Interface• Voice synthesizer


Data comms.system

Transpondersystem

Radarsystem

Aircraftcomms.

Telephonesystem

Flight plandatabase

Backupposition

processor

Positionprocessor

Comms.processor

Backup comms.processor

Aircraftsimulation

system

Weather mapsystem

Accountingsystem

Controllerinfo. system

Controllerconsoles

Activity loggingsystem

ATC systemarchitecture


Inter-disciplinary involvement

ATC systemsengineering

Electronicengineering

Electricalengineering

User interfacedesign

Mechanicalengineering

Architecture

Structuralengineering

Softwareengineering

Civilengineering


Embedded systems Computing systems are everywhere Most of us think of “desktop” computers

• PC’s

• Laptops

• Mainframes

• Servers

But there’s another type of computing system• Far more common...


Embedded systems overview Embedded computing systems

• Computing systems embedded within electronic devices

• Hard to define. Nearly any computing system other than a desktop computer

• Billions of units produced yearly, versus millions of desktop units

• Perhaps 50 per household and per automobile

Computers are in here...

and here...

and even here...

Lots more of these, though they cost a lot less each.


A “short list” of embedded systems

And the list goes on and on

Anti-lock brakesAuto-focus camerasAutomatic teller machinesAutomatic toll systemsAutomatic transmissionAvionic systemsBattery chargersCamcordersCell phonesCell-phone base stationsCordless phonesCruise controlCurbside check-in systemsDigital camerasDisk drivesElectronic card readersElectronic instrumentsElectronic toys/gamesFactory controlFax machinesFingerprint identifiersHome security systemsLife-support systemsMedical testing systems

ModemsMPEG decodersNetwork cardsNetwork switches/routersOn-board navigationPagersPhotocopiersPoint-of-sale systemsPortable video gamesPrintersSatellite phonesScannersSmart ovens/dishwashersSpeech recognizersStereo systemsTeleconferencing systemsTelevisionsTemperature controllersTheft tracking systemsTV set-top boxesVCR’s, DVD playersVideo game consolesVideo phonesWashers and dryers


Some common characteristics of embedded systems

Single-functioned• Executes a single program, repeatedly

Tightly-constrained• Low cost, low power, small, fast, etc.

Reactive and real-time• Continually reacts to changes in the system’s environment

• Must compute certain results in real-time without delay


An embedded system example -- a digital camera

Microcontroller

CCD preprocessor Pixel coprocessorA2D

D2A

JPEG codec

DMA controller

Memory controller ISA bus interface UART LCD ctrl

Display ctrl

Multiplier/Accum

Digital camera chip

lens

CCD

• Single-functioned -- always a digital camera

• Tightly-constrained -- Low cost, low power, small, fast

• Reactive and real-time -- only to a small extent


Design challenge – optimizing design metrics

Obvious design goal:• Construct an implementation with desired functionality

Key design challenge:• Simultaneously optimize numerous design metrics

Design metric• A measurable feature of a system’s implementation

• Optimizing design metrics is a key challenge



Common metrics• Unit cost: the monetary cost of manufacturing each copy of the

system, excluding NRE cost

• NRE cost (Non-Recurring Engineering cost): The one-time monetary cost of designing the system

• Size: the physical space required by the system

• Performance: the execution time or throughput of the system

• Power: the amount of power consumed by the system

• Flexibility: the ability to change the functionality of the system without incurring heavy NRE cost



Common metrics (continued)• Time-to-prototype: the time needed to build a working version of the

system

• Time-to-market: the time required to develop a system to the point that it can be released and sold to customers

• Maintainability: the ability to modify the system after its initial release

• Correctness, safety, many more


Design metric competition -- improving one may worsen others

Expertise with both software and hardware is needed to optimize design metrics

• Not just a hardware or software expert, as is common

• A designer must be comfortable with various technologies in order to choose the best for a given application and constraints

SizePerformance

Power

NRE cost

Microcontroller

CCD preprocessor Pixel coprocessorA2D

D2A

JPEG codec

DMA controller

Memory controller ISA bus interface UART LCD ctrl

Display ctrl

Multiplier/Accum

Digital camera chip

lens

CCD

Hardware

Software


Robotic SystemRobotic System

Proxímetro IR

Cámara de visión

(pan-and-tilt)

Unidad inercial

Módem BluetoothBlueSMiRF (WRL-00582)

Video


Robotic System

• Mecanica + Control + Computacion

– Ingeniería de reversa (servomecanismos, controlador, programación)

– Mecánicas (cabeza, tobillos), comunicación inalámbrica, hardware para control,

– Sistema de programación, interfaz bidireccional para los servos…

• Percepción

– Sensores: Visión, Infrarrojos, Unidad Inercial

– Reconstrucción 3D Monocular

• SLAM Visual

– Odometría visual, Navegación Inercial (IMU), SLAM Visual, etc.

• Obtención de Modelos y Desarrollo de Simulador

– Geométrico, Cinemático, Dinámico

• Control Cinemático y Dinámico

– Control articular, control cinemático, control dinámico (ZMP, FRI)

• Aplicaciones

– Reconocer pelota, Evitar y reconocer obstáculos y marcas, Caminar hacia la pelota, conducir la pelota, Penalties (tirar y parar), coordinacion con otros robots, Pruebas RoboCup, Futbolistas.


Robotic System ApplicationRobotic System Application


Electric SCADA System


Web-Based Software System

http://people.csail.mit.edu/hal/mobile-apps-spring-08/videos/flare.mpg


Key points System engineering involves input from a range of

disciplines Emergent properties are properties that are characteristic

of the system as a whole and not its component parts System architectural models show major sub-systems and

inter-connections. They are usually described using block diagrams

System component types are sensor, actuator, computation, co-ordination, communication and interface


Systems engineering is hard! There will never be an easy answer to the problems of complex system development

Software engineers do not have all the answers but may be better at taking a systems viewpoint

Disciplines need to recognise each other’s strengths and actively rather than reluctantly cooperate in the systems engineering process

Conclusion

©Sommerville 2000, Medvidovic 2006, Mejia 2009Systems EngineeringSlide 1 Systems Engineering l...

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