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Chapter 2 Socio-technical Systems _Computer-based System Engineering_

VIEWS: 9 PAGES: 34

									            Chapter 2 , Cont…
     Socio-technical Systems
    (Computer-based System Engineering)




1
            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
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    Intruder alarm system Model OR
               Architecture
    Movement                   Door
     sensors                  sensors



                 Alarm
                controller

                                           External
                                         control centre
                 Voice       Telephone
     Siren
               synthesizer     caller



3
     Component types in alarm
            system
    • Sensor
       – Movement sensor, door sensor (detect door
         opening, and movement in the rooms)
    • Siren
       – Siren- warning when intruder is suspected ‫.شك‬
    • Communication
       – Telephone caller, make external calls to police.
    • Co-ordination
       – Alarm controller, control the operation of the
         system.
    • Interface
       – Voice synthesizer, a synthesize message
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         giving the location of the intruder.
    Functional system components

• Sensor components
• Actuator components (siren)
• Computation components (Alarm
  Controller)
• Communication components
• Co-ordination components
• Interface components

5
            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




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     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



7
  ATC (air traffic) System Architecture
             Large System
  Radar       Transponder     Da ta comms.           Aircraft           Telephone
 system         system           system              comms.              system




Position           Backup                    Comms   .              Backup comms.
processor          position                  processor                processor
                  processor




 Aircraft                      Flight plan
simulation                      database
  system



Weather map
  system

                               Control ler                              Controller
Accounting                    info. system                               consoles
  system

                                                 Activity logging
                                                     system
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       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.



   9
     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 .
10
          5- System Integration
• 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


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     System Integration cont…
Incremental integrated process is the best approach
because:

• 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.)
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       6- System installation- problems

• 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
  13
              System operation
• 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


  14
             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
   15
  called legacy systems
       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
  16
     Organizations/people/systems

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




17
 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

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              System hierarchies
 Town

     Street

         Building
               Heating    Power       Water
               system     system     system
               Security   Lighting    Waste
                system    system     system




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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.


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




     Procurement/development/ operational processes
21
 System procurement processes
• procurement processes: is embedded
  within the client organization that will
  buy and use the system.




22
        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


   23
       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,

  24
  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


  25
     Contractor/Sub-contractor
              model
                       System
                      customer



                       Principal
                      contractor




Sub-contractor 1   Sub-contractor 2   Sub-contr actor 3


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       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.
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             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;

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     Legacy system components




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         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.



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Alternative way for the component of legacy
          system : Layered model

           Socio-technical system


                        Business processes


                      Application software

                       Support software


                            Hardware
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      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.




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                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
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              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
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