Slide 2
Objectives
To explain what a socio-technical system is and
Distinction between this and a computer-based system
To introduce the concept of emergent System Properties
Such as reliability and security
To explain system engineering and system procurement
Processes
To explain why the organisational context of a system
Affects its design and use
To discuss legacy systems and why these are critical
Many businesses
Slide 3
Topics covered
Emergent System Properties
Systems Engineering
Organizations, people and computer systems
Legacy systems
Slide 4
What is a system?
A purposeful collection of inter-related components
Working together to achieve 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
Slide 5
System categories
Technical computer-based systems
• Systems that include hardware and software
Where the operators and operational processes are
Not normally considered to be part of the system.
The system is not self-aware.
Socio-technical systems
• Systems that include technical systems but also
Operational processes and people who use and
Interact with the technical system. socio-technical
Systems are governed by organisational schemas ies and
Rules.
Slide 6
Socio-technical system characteristics
Emergent properties
• Properties of the system of a whole that depend on the System
Components and their relationships.
Non-deterministic
• They do not always produce the same output when presented
With the same input because the systems's behaviour is
Partially dependent on human operators.
Complex relationships with organisational objectives
• The extent to which the system supports organisational
Objectives does not just depend on the system itself.
Slide 7
Emergent properties
Properties of the system as a whole rather
Properties that can be derived from
Properties of components of a system
Emergent properties are a consequence of
Relationships between system components
They can therefore only be assessed and
Measured once the components have been
Integrated into a system
Slide 8
Examples of emergent properties
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Volume the volume of a system (the total space occupied) varies depending on how
Component assemblies are arranged and connected.
Reliability System Reliability depends on component reliability but unexpected interactions can
Cause new types of failure and therefore affect the reliability of the system.
Security the security of the system (its ability to resist attack) is a complex property that
Cannot be easily measured. Attacks may be devised that were not anticipated by
System designe RS and so may defeat built-in safegua RDS.
Repairability this property reflects how easy it is to fix a problem with the system once it has been
Discovered. It depends on being AB le to diagno se the problem, access the components
That are faulty and modify or replace these components.
Usability this property reflects how easy it is to use the system. It depends on the technical
System components, its operators and Its Operating env ironment.
Slide 9
Types of emergent property
Functional Properties
• These appear when all the parts of a system work together
Achieve some objective. For example, a bicycle has
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.
Slide 10
Because of Component Inter-dependencies,
Faults can be propagated through the system.
System failures often occur because
Unforeseen inter-relationships
Components.
It is probably impossible to anticipate all
Possible component relationships.
Software reliability measures may give a false
Picture of the system reliability.
System Reliability Engineering
Slide 11
Hardware Reliability
• What is the probability of a hardware component failing and
How long does it take to repair that component?
Software Reliability
• How likely is it that a software component will produce
Incorrect output. software failure is usually distinct from
Hardware failure in that software does not wear out.
Operator Reliability
• How likely is it that the operator of a system will make an error?
Influences on Reliability
Slide 12
Reliability relationships
Hardware failure can generate spurious signals
That are outside the range of inputs expected
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.
Slide 13
The 'shall-not' Properties
Properties such as performance and reliability
Can be measured.
However, some properties are properties that
System shocould not exhibit
• Safety-the system shocould not behave in an unsafe
Way;
• Security-the system shocould not permit unauthorised
Use.
Measuring or assessing these properties is very
Hard.
Slide 14
Systems Engineering
Specifying, designing, implementing, validating,
Deploying and maintaining socio-technical
Systems.
Concerned with the services provided by
System, constraints on its construction and
Operation and the ways in which it is used.
Slide 15
The System Engineering Process
Usually follows a 'waterfull' model because of the need
For parallel development of different parts of the system
• Little scope for iteration between phases because hardware
Changes are very expensive. Software may have
Compensate for hardware problems.
Inevitably involves engineers from different disciplines
Who must work together
• Much scope for misunderstanding here. Different disciplines
Use a different vocabulary and much negotiation is required.
Engineers may have personal agendas to fulfil.
Slide 16
The Systems Engineering Process
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Slide 18
System Requirements Definition
Three types of requirement defined at this stage
• Abstract functional requirements. system functions
Are defined in an abstract way;
• System Properties. non-functional requirements
The system in general are defined;
• Undesirable characteristics. Unacceptable System
Behaviour is specified.
Shocould also define overall organisational
Objectives for the system.
Slide 19
System objectives
Shocould define why a system is being procured
For a special environment.
Functional Objectives
• To provide a fire and intruder alarm system for
Building which will provide internal and external
Warning of fire or unauthorized intrusion.
Organisational objectives
• To ensure that the normal functioning of Work carried
Out in the building is not seriously disrupted
Events such as fire and unauthorized intrusion.
Slide 20
System Requirements Problems
Complex systems are usually developed
Address Wicked problems
• Problems that are not fully understood;
• Changing as the system is being specified.
Must anticipate Hardware/communications
Developments over the lifetime of the system.
Hard to define non-functional requirements
(Particle) without knowing
Component structure of the system.
Slide 21
The system design process
Partition requirements
• Organise requirements into related groups.
Identify sub-systems
• Identify a set of sub-systems which collectively can meet
System requirements.
Assign requirements to sub-systems
• Causes special problems when cots are integrated.
Specify sub-system functionality.
Define sub-system interfaces
• Critical activity for parallel sub-system development.
Slide 22
The system design process repaesqirmdutatueieoebestifqsmi rnnu-dpsosiusnttnuieeniiysegtrcnfbcfsenytti-
Slide 23
System Design Problems
Requirements partitioning to hardware,
Software and human components may involve
Lot of negotiation.
Difficult design problems are often assumed
Be readily solved using software.
Hardware platforms may be inappropriate
Software requirements so software must
Compensate for this.
Slide 24
Requirements and Design
Requirements engineering and System Design
Are inextricably linked.
Constraints posed by the system's Environment
And other systems limit design choices so
Actual design to be used may be a requirement.
Initial design may be necessary to structure
Requirements.
As you do design, you learn more about
Requirements.
Slide 25
Spiral Model of requirements/Design
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Slide 26
System modelling
An Explain tural model presents an abstract View
Of the sub-systems making up a system
May include major information flows
Sub-systems
Usually presented as a block digoal
May identify different types of functional
Component in the Model
Slide 27
Burglar Alarm System scavoomeyoilrlnclnaeettrrhresis
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Slide 28
Sub-system description
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Movement sensors detects movement in the rooms monitored by the System
Door sensors detects door opening in the external doors of the building
Alarm Controller controls the operation of t he System
Siren emits an audible warning when an intruder is suspected
Voice Synthesizer Synthesizes a voice message giving the location of the suspected intruder
Telephone caller makes external callto notif y security, the police, etc.
Slide 30
Sub-system development
Typically parallel projects developing
Hardware, software and communications.
May involve some COTS (inclucial off-the-shelf)
Systems procurement.
Lack of communication implements SS implementation
Teams.
Bureaucratic and slow mechanic
Proposing system changes means that the development
Schedule may be extended because of the need
Rework.
Slide 31
The process of putting hardware, software and
People together to make a system.
Shocould be tackled incrementally so that subsystems
Are integrated one at a time.
Interface problems between sub-systems are
Usually found at this stage.
May be problems with uncoordinated deliveries
Of system components.
System integration
Slide 32
After completion, the system has to be installed
In the customer's Environment
• Environmental assumptions may be incorrect;
• May be human resistance to the introduction
A new system;
• System may have to coexist with alternative
Systems for some time;
• May be physical installation problems (e.g.
Cabling problems );
• Operator training has to be identified.
System Installation
Slide 33
System Evolution
Large systems have a long lifetime. They must evolve
Meet changing requirements.
Evolution is inherently costly
• Changes must be analyzed from a technical and business
Perspective;
• Sub-systems interact so unanticipated problems can arise;
• There is rarely a rationale for original design decisions;
• System structure is already upted as changes are made to it.
Existing systems which must be maintained are
Sometimes called legacy systems.
Slide 34
System decommissioning
Taking the system out of service after its useful
Lifetime.
May require removal of materials (e.g.
Dangerous Chemicals) which pollute
Environment
• Shoshould be planned for in the system design
Encapsulation.
May require data to be restructured and
Converted to be used in some other system.
Slide 35
Organisations/people/Systems
Socio-technical systems are organisational
Systems intended to help deliver some
Organisational or business goal.
If you do not understand the organisational
Environment where a system is used, the system
Is less likely to meet the real needs of
Business and its users.
Slide 36
Human and organisational factors
Process changes
• Does the system require changes to the work
Processes in the environment?
Job changes
• Does the system de-skill the users in an environment or
Cause them to change the way they work?
Organisational changes
• Does the system change the political power structure in
An organization?
Slide 37
Organisational Processes
The processes of Systems Engineering overlap and
Interact with organisational procurement processes.
Operational processes are the processes involved in
Using the system for its intended purpose. For new
Systems, these have to be defined as part of the system
Design.
Operational processes shoshould be designed to be flexible
And shoshould not force operations to be done in a particle
Way. It is important that human operators can use their
Initiative if problems arise.
Slide 39
System procurement
Acquiring a system for an organization to meet some
Need
Some system specification and specified tural design is
Usually necessary before procurement
• You need a specification to let a contract for System
Development
• The specification may allow you to buy a specified cial off-theshelf
(COTS) system. Almost always cheaper than developing
A system from scratch
Large Complex systems usually consist of a mix of off
Shelf and specially designed components.
Procurement processes for these different types
Component are usually different.
Slide 40
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Slide 41
Procurement issues
Requirements may have to be modified to match
The capabilities of off-the-shelf components.
The requirements specification may be part
The contract for the development of the system.
There is usually a contract negotiation period
Agree changes after the contractor to build
System has been selected.
Slide 42
Contractors and sub-contractors
The procurement of large hardware/software
Systems is usually based around some principal
Contractor.
Sub-contracts are issued to other suppliers
Supply parts of the system.
Customer liases with the principal contractor and
Does not deal directly with sub-contractors.
Slide 43
Contractor/sub-contractor Model
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Slide 44
Legacy systems
Socio-technical systems that have been developed using
Old or obsolete technology.
Crucial to the operation of a business and it is often too
Risky to discard these systems
• Bank Customer accounting system;
• Aircraft Maintenance System.
Legacy systems constrain new business processes and
Consume a high proportion of company budgets.
Slide 46
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 ages.
Application Data-often incomplete and inconsistent.
Business processes-may be constrained by software
Structure and functionality.
Business continuity ies and rules-may be implicit and
Embedded in the system software.
Slide 47
Socio-hardware support application business
Slide 48
Key Points
Socio-technical systems include computer hardware,
Software and people and are designed to meet some
Business goal.
Emergent properties are properties that are characteristic
Of the system as a whole and not its component parts.
The Systems Engineering Process has des specification,
Design, development, integration and testing. System
Integration is special critical.
Ian Sommerville 2004 7 t software engineering, 7th edition.
Slide 49
Key Points
Human and organisational factors have a significant
Effect on the operation of socio-technical systems.
There are complex interactions between the processes
System procurement, development and operation.
A legacy system is an old system that continues
Provide essential services.
Legacy systems include business processes, Application
Software, support software and system hardware.
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