1

Chapter 2 , Cont…

Socio-technical Systems

(Computer-based System Engineering)

2

3 -System 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

3

Intruder alarm system Model OR Architecture

Alarmcontroller

Voicesynthesizer

Movementsensors

Siren

Doorsensors

Telephonecaller

Externalcontrol centre

4

Component types in alarm system

• Sensor– Movement sensor, door sensor (detect door opening,

and movement in the rooms)• Siren

– Siren- warning when intruder is suspectedشك .• Communication

– Telephone caller, make external calls to police.• Co-ordination

– Alarm controller, control the operation of the system.• Interface

– Voice synthesizer, a synthesize message giving the location of the intruder.

5

Functional system components

• Sensor components

• Actuator components (siren)

• Computation components (Alarm Controller)

• Communication components

• Co-ordination components

• Interface components

6

System components• Sensor components

– Collect information from the system’s environment e.g. radars in an air traffic control system

• Computation components– Carry out some computations on an input to

produce an output e.g. a floating point processor in a computer system

7

System components continued…• Communication components

– Allow system components to communicate with each other e.g. network linking distributed computer

• Interface components – Facilitate the interactions of other system

components e.g. operator interface

• All components are now usually software controlled

8

ATC (air traffic) System ArchitectureLarge System

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

9

4 -Sub-system development• Typically parallel projects developing the hardware,

software and communications from scratch.

• May involve some COTS (Commercial Off-The-Shelf) systems.. Bought for integration to system.

• COTS usually cheaper than to develop special-purpose

component• COTS may not meet the requirement exactly. (problem)• If COTS product available it is worth to expense your time

of rethinking in the design.

10

Sub-system development

• When a problem is encountered in a system, a system need modification.

• For systems that involve extensive hardware, making modification after manufacturing has started is very expensive…

• Solution

“Work arounds” that include software change that include software change requirement because software is more flexible .

11

• The process of putting hardware, software and people together to make a system

• The system may be integrated using:

1- a “big bang approach”: all subsystems are integrated at the same time.

2- incremental integrated process: the sub-systems are integrated one at a time

5 -System Integration

12

System Integration cont…

Incremental integrated process is the best approachbecause:

• It reduce the cost of error location. In “big bang approach” the error may be from any

of these subsystems. While in “incremental process” the errors are probably on the new subsystem or in the interaction between the existing subsystem and the new subsystem.

Incremental integrated process problem:• Interface problems between sub-systems are usually

found at this stage (integration + testing) (Data flow( in / out ) at the boundary.)

13

• Environmental assumptions may be incorrect

• May be human resistance to the introduction of a new system

• May be physical installation problems (e.g. cabling problems)

• Operator training has to be identified

6 -System installation- problems

14

• Users may use the system in a way which is not suitable by system designers

• May reveal problems in the interaction with other systems– Physical problems of incompatibility– Increased operator error rate because of

inconsistent interfaces

System operation

15

7 -System evolution• Large and complex systems have a long lifetime. They must

evolve to meet changing requirements[ error in system or change environment]

• Evolution is inherently costly because:– Changes must be analyzed from a technical and business

perspective [after changing must get the same goal of the system]

– Sub-systems interact [change in subsystem may affects on other subsystems]so problems can arise

– As systems Age: System structure is corrupted as changes are made to it, so the cost of making changes increases

• Existing systems which must be maintained are sometimes called legacy systems

16

8 -System decommissioning

• Taking the system out of service after its useful operational lifetime

Regards to Hardware:• May require removal of materials (e.g. dangerous

chemicals) which pollute the environment

Regards to software:• May require data to be restructured and converted

to be used in some other system

17

Organizations/people/systems

• If you do not understand the organizational environment where a system is used, then the system is rejected

18

Systems and their environment

• Systems are exist in an environment

• The system is intended to make some changes in its environment, heating system changes its environment by increasing or decreasing its temperature.

• Environment affects the functioning of the system

e.g. system may require electrical supply from its environment

19

System hierarchies

Securitysystem

Heatingsystem

Lightingsystem

Powersystem

Wastesystem

Watersystem

Town

Street

Building

20

Human and organizational factors that affect the system design:

• Process changes, does the system require changes to the work processes in the environment? If so, training is required. If so they may resist the introduction to the system.

• Job changes, does the system de-skill the users in an environment or cause them to change the way they work? If so they may resist the introduction to the system.

• Organizational changes, does the system change the political power structure in an organization?

e.g. Those who know how to operate in a Complex system have a great deal of political power.

21

Organizational processes

• The processes of systems engineering interact with procurement processes and the process of using and operating the system.

Procurementprocess

Operationalprocess

Developmentprocess

Procurement/development/ operational processes

22

System procurement processes

• procurement processes: is embedded within the client organization that will buy and use the system.

23

System procurement process

• This process concerned with: deciding on the best suppliers of that system and the best way for the organization to acquire a system to meet some need

• Some system specification is usually necessary – You need a high level specification of what the system

should do, in order to design or build (buy) a system development

– The specification may allow you to buy a commercial off-the-shelf (COTS) system. Almost always cheaper than developing a system from scratch

24

System procurement process Issues

• Requirements may have to be modified to match the capabilities of off-the-shelf components

• The requirements specification may be part of the contract for the development of the system.

• After the contractor to build the system has been selected, there is usually a contract negotiation period for further changes to the requirements to be agreed upon,

25

Contractors and sub-contractors• The procurement of large hardware/software

systems is usually based on some principal contractor

• Sub-contracts are issued to other suppliers to supply parts of the system

• Customer deals with the principal contractor and does not deal directly with sub-contractors

26

Contractor/Sub-contractor model

Sub-contractor 2Sub-contractor 1 Sub-contractor 3

Principalcontractor

Systemcustomer

27

Organizational processes, Operational processes

• Operational processes : the using of the system.

• Operational processes should be designed to be flexible and should not force operations to be done in a particular way.

• It is important that human operators can use their initiative if problems arise.

• Example:• Operators of Air traffic control system follow specific

processes when the aircraft enter and leave airspace, when they have to change height , speed.

28

Legacy systems

• It is a Socio-technical systems that have been developed in the past and often use old or obsolete technology.

• it is often too risky to replace these systems, because the new system may not work well– Bank customer accounting system;

29

Legacy system components

Systemhardware

Businessprocesses

Applicationsoftware

Business policiesand rules

Support software

Application data

ConstrainsUsesUsesRuns-onRuns-on

Embedsknowledge of

Uses

30

Legacy system components

• Hardware - may be obsolete mainframe hardware.

• Support software - may rely on support software from suppliers who are no longer in business.

• Application software - may be written in obsolete programming languages.

• Application data - often inconsistent and may be duplicated.

31

Socio-technical system

Hardware

Support software

Application software

Business processes

Alternative way for the component of legacy system : Layered model

32

Layered Legacy system

• Each layer depend on the layer below it

• Changing on layer may require consequent changes to layers that are above an below the changed layer.

33

Key points• System engineering involves input from a

range of disciplines, SW, HW, People and Environment.

• 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

34

Key points• The systems engineering process is

usually a waterfall model and includes specification, design, development and integration.

• System procurement is concerned with deciding which system to buy and who to buy it from