software engineering chapter 2 socio-technical systems ku-yaw chang [email protected]...
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Software EngineeringSoftware Engineering
Chapter 2 Chapter 2 Socio-technical systemsSocio-technical systems
Ku-Yaw ChangKu-Yaw [email protected]@mail.dyu.edu.tw
Assistant ProfessorAssistant ProfessorDepartment of Computer Science and Information EngineeringDepartment of Computer Science and Information Engineering
Da-Yeh UniversityDa-Yeh University
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ObjectivesObjectives
Know what is meant by socio-technical system and Know what is meant by socio-technical system and understand the difference between a technical computer-understand the difference between a technical computer-based system and a socio-technical systembased system and a socio-technical systemHave been introduced to the concept of emergent Have been introduced to the concept of emergent system properties such as reliability, performance, safety system properties such as reliability, performance, safety and securityand securityUnderstand the activities that are involved in the systems Understand the activities that are involved in the systems engineering processengineering processUnderstand why the organizational context of a system Understand why the organizational context of a system affects its design and useaffects its design and useKnow what is meant by a ‘legacy system’, and why these Know what is meant by a ‘legacy system’, and why these systems are often critical to the operation of many systems are often critical to the operation of many businessbusiness
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PreamblePreamble
What is a system?What is a system? A purposeful collection of inter-related components A purposeful collection of inter-related components
that work together to achieve some objective.that work together to achieve some objective. A system may include software, mechanical, electrical A system may include software, mechanical, electrical
and electronic hardware and be operated by people.and electronic hardware and be operated by people. System components are dependent on other System components are dependent on other
system componentssystem components The properties and behavior of system components The properties and behavior of system components
are inextricably inter-mingledare inextricably inter-mingled
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PreamblePreamble
System categoriesSystem categories Technical computer-based systemsTechnical computer-based systems
Systems that include Systems that include hardwarehardware and and softwaresoftware but where the but where the operators and operational processes are not normally operators and operational processes are not normally considered to be part of the system. The system is not self-considered to be part of the system. The system is not self-aware.aware.
Socio-technical systemsSocio-technical systemsSystems that include technical systems but also Systems that include technical systems but also operational operational processesprocesses and and peoplepeople who use and interact with the who use and interact with the technical system. Socio-technical systems are governed by technical system. Socio-technical systems are governed by organizational policies and rules.organizational policies and rules.
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PreamblePreamble
Socio-technical system characteristicsSocio-technical system characteristics Emergent propertiesEmergent properties
Properties of the system of a whole that depend on the Properties of the system of a whole that depend on the system components and their relationships.system components and their relationships.
Non-deterministicNon-deterministicThey do not always produce the same output when They do not always produce the same output when presented with the same input because the system’s presented with the same input because the system’s behavior is partially dependent on human operators.behavior is partially dependent on human operators.
Complex relationships with organizational objectivesComplex relationships with organizational objectivesThe extent to which the system supports organizational The extent to which the system supports organizational objectives does not just depend on the system itself.objectives does not just depend on the system itself.
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ContentsContents
2.1 Emergent system properties2.1 Emergent system properties
2.2 System engineering2.2 System engineering
2.3 Organizations, people and computer systems2.3 Organizations, people and computer systems
2.4 Legacy systems2.4 Legacy systems
2.5 Exercises2.5 Exercises
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2.1 Emergent system properties2.1 Emergent system properties
Properties of the system as a wholeProperties of the system as a whole rather than rather than properties that can be derived from the properties that can be derived from the properties of components of a systemproperties of components of a system a consequence of the relationships between system a consequence of the relationships between system
componentscomponents only be assessed and measured once the only be assessed and measured once the
components have been integrated into a systemcomponents have been integrated into a system
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Examples of emergent propertiesExamples of emergent properties
VolumeVolume Total space occupiedTotal space occupied
ReliabilityReliability Depends on component reliabilityDepends on component reliability Unexpected interactions cause new failureUnexpected interactions cause new failure
SecuritySecurity Ability to resist attackAbility to resist attack
ReparabilityReparability How easy to fix a problemHow easy to fix a problem
UsabilityUsability How easy to use the systemHow easy to use the system
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Types of emergent propertiesTypes of emergent properties
Functional emergent propertiesFunctional emergent properties All the parts of a system work together to achieve All the parts of a system work together to achieve
some objectivesome objectivea bicycle has the functional property of being a transportation a bicycle has the functional property of being a transportation device once it has been assembled from its components.device once it has been assembled from its components.
Non-functional emergent propertiesNon-functional emergent properties Relate to the behavior of the system in its operational Relate to the behavior of the system in its operational
environmentenvironmentReliability, performance, safety, and securityReliability, performance, safety, and security
Critical for computer-based systemsCritical for computer-based systemsFailure to achieve some minimal defined level in these Failure to achieve some minimal defined level in these properties may make the system unusable.properties may make the system unusable.
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Complexity of emergent propertiesComplexity of emergent properties
Consider the property of system reliabilityConsider the property of system reliability Because of component inter-dependencies, Because of component inter-dependencies,
faults can be propagated through the system.faults can be propagated through the system. System failures often occur because of System failures often occur because of
unforeseen inter-relationships between unforeseen inter-relationships between components.components.
It is probably impossible to anticipate all It is probably impossible to anticipate all possible component relationships.possible component relationships.
Software reliability measures may give a false Software reliability measures may give a false picture of the system reliability.picture of the system reliability.
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Influences on reliabilityInfluences on reliability
Hardware reliabilityHardware reliability What is the probability of a hardware component What is the probability of a hardware component
failing and how long does it take to repair that failing and how long does it take to repair that component?component?
Software reliabilitySoftware reliability How likely is it that a software component will produce How likely is it that a software component will produce
an incorrect output.an incorrect output. Software failure is usually distinct from hardware Software failure is usually distinct from hardware
failure in that software does not wear out. failure in that software does not wear out.
Operator reliabilityOperator reliability How likely is it that the operator of a system will make How likely is it that the operator of a system will make
an error?an error?
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Reliability relationshipsReliability relationships
Hardware failure can generate spurious signals Hardware failure can generate spurious signals that are outside the range of inputs expected by that are outside the range of inputs expected by the software.the software.
Software errors can cause alarms to be Software errors can cause alarms to be activated which cause operator stress and lead activated which cause operator stress and lead to operator errors.to operator errors.
The environment in which a system is installed The environment in which a system is installed can affect its reliability.can affect its reliability.
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The ‘shall-not’ propertiesThe ‘shall-not’ properties
Properties such as performance and reliability Properties such as performance and reliability can be measured.can be measured.However, some properties are properties that However, some properties are properties that the system the system should not exhibitshould not exhibit Safety - the system should not behave in an unsafe Safety - the system should not behave in an unsafe
way;way; Security - the system should not permit unauthorised Security - the system should not permit unauthorised
use.use.
Measuring or assessing these properties is very Measuring or assessing these properties is very hardhard Knowing a system is insecure only when someone Knowing a system is insecure only when someone
breaks into itbreaks into it
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ContentsContents
2.1 Emergent system properties2.1 Emergent system properties
2.2 System engineering2.2 System engineering
2.3 Organizations, people and computer systems2.3 Organizations, people and computer systems
2.4 Legacy systems2.4 Legacy systems
2.5 Exercises2.5 Exercises
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System engineeringSystem engineering
The activity of specifying, designing, The activity of specifying, designing, implementing, validating, deploying and implementing, validating, deploying and maintaining socio-technical systemsmaintaining socio-technical systems
Concerned withConcerned with SoftwareSoftware HardwareHardware System’s interactions with users and its environmentSystem’s interactions with users and its environment
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The systems engineering processThe systems engineering process
Systemintegration
Sub-systemdevelopment
System
design
Requirementsdefinition
Systeminstallation
System
evolution
Systemdecommissioning
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Important distinctionsImportant distinctions
Limited scope for rework during system Limited scope for rework during system developmentdevelopment Little scope for iteration between phases because Little scope for iteration between phases because
hardware changes are very expensivehardware changes are very expensive
Interdisciplinary involvementInterdisciplinary involvement Inevitably involve engineers from different disciplines Inevitably involve engineers from different disciplines
who must work togetherwho must work together Different engineers use different terminology and Different engineers use different terminology and
conventionsconventions
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Inter-disciplinary involvementInter-disciplinary involvement
ATC systems
engineering
Electronic
engineering
Electrical
engineering
User interface
design
Mechanical
engineering
Architecture
Structural
engineering
Software
engineering
Civil
engineering
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2.2.1 System requirements definition2.2.1 System requirements definition
SpecifySpecify What the system should do (its functions)What the system should do (its functions) Essential and desirable system propertiesEssential and desirable system properties
Involve consultations with system customers/end-usersInvolve consultations with system customers/end-users
Derive three types of requirementDerive three types of requirement Abstract functional requirementsAbstract functional requirements
Basic functions at an abstract levelBasic functions at an abstract level System propertiesSystem properties
Non-functional emergent system propertiesNon-functional emergent system properties Characteristics that the system must no exhibitCharacteristics that the system must no exhibit
Must not do vs. should doMust not do vs. should do e.g. Too much information should not be presented to the controllere.g. Too much information should not be presented to the controller
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2.2.1 System requirements definition2.2.1 System requirements definition
To establish a set of overall objectives that the To establish a set of overall objectives that the system should meetsystem should meet Functional objectivesFunctional objectives
To provide a fire and intruder alarm system for the building To provide a fire and intruder alarm system for the building which will provide internal and external warning of fire or which will provide internal and external warning of fire or unauthorized intrusion.unauthorized intrusion.
Organizational objectivesOrganizational objectivesTo ensure that the normal functioning of work carried out in To ensure that the normal functioning of work carried out in the building is not seriously disrupted by events such as fire the building is not seriously disrupted by events such as fire and unauthorized intrusion.and unauthorized intrusion.
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2.2.1 System requirements definition2.2.1 System requirements definition
Complex systems are usually developed to Complex systems are usually developed to address address wicked problemswicked problems So many related entities that there is no definitive So many related entities that there is no definitive
problem specificationproblem specification An extreme exampleAn extreme example
Earthquake planningEarthquake planning
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2.2.2 System design2.2.2 System design
How the system functionality is to be provided by How the system functionality is to be provided by the components of the systemthe components of the system Partition requirementsPartition requirements
Analyze requirements and organize them into related groupsAnalyze requirements and organize them into related groups Identify sub-systemsIdentify sub-systems
Individually or collectively meet the requirementsIndividually or collectively meet the requirements Assign requirements to sub-systemsAssign requirements to sub-systems
Never a clean match between requirements partitions and Never a clean match between requirements partitions and identified sub-systemsidentified sub-systems
Specify sub-system functionalitySpecify sub-system functionality Define sub-system interfacesDefine sub-system interfaces
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The system design processThe system design process
Partitionrequirements
Identifysub-systems
Assign requirementsto sub-systems
Specify sub-systemfunctionality
Define sub-systeminterfaces
Double-ended arrowsDouble-ended arrows A lot of feedback and iteration from one stage to another in the A lot of feedback and iteration from one stage to another in the
design processdesign process
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Requirements and designRequirements and design
Requirements affect design decisions and vice Requirements affect design decisions and vice versaversa In practice, the are inextricably linkedIn practice, the are inextricably linked
Constraints posed by the existing systems mayConstraints posed by the existing systems may Limit design choicesLimit design choices These choices may be specified in the requirementsThese choices may be specified in the requirements Initial design may be necessary to structure the Initial design may be necessary to structure the
requirements.requirements.
As you do design, you learn more about the As you do design, you learn more about the requirements.requirements.
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Spiral model of requirements/designSpiral model of requirements/design
System Requirements and Design
ProblemDefinition
Review andAssessment
RequirementsElicitation and
Analysis
ArchitecturalDesign
Start
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2.2.3 System modeling2.2.3 System modeling
An architectural modelAn architectural model A set of components (sub-systems)A set of components (sub-systems) and their and their
relationshipsrelationships An abstract viewAn abstract view of the sub-systems making up a of the sub-systems making up a
systemsystem More appropriate to classify sub-systems according to More appropriate to classify sub-systems according to
their functiontheir functionBefore making decisions about hardware/software trade-offsBefore making decisions about hardware/software trade-offs
Illustrated graphically and presented as Illustrated graphically and presented as a block a block diagramdiagram
Be supplemented by brief descriptions of each subsystemBe supplemented by brief descriptions of each subsystemMay be used for all sizes of systemMay be used for all sizes of system
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A simple burglar alarm systemA simple burglar alarm system
Alarmcontroller
Voicesynthesiser
Movementsensors
Siren
Doorsensors
Telephonecaller
Externalcontrol centre
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Sub-system descriptionSub-system description
Sub-system Description
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 the 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 calls to notify security, the police, etc.
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ATC system architectureATC system architecture
Data comms.system
Transpondersystem
Radarsystem
Aircraftcomms.
Telephonesystem
Flight plandatabase
Backupposition
processor
Position
processor
Comms.
processor
Backup comms.
processor
Aircraft
simulationsystem
Weather map
system
Accountingsystem
Controllerinfo. system
Controllerconsoles
Activity loggingsystem
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2.2.4 Sub-system development2.2.4 Sub-system development
The implementation may involve startingThe implementation may involve starting Another system engineering processAnother system engineering process A software processA software process
Commercial off-the-shelf (COTS) systems are Commercial off-the-shelf (COTS) systems are bought for integration into the systembought for integration into the system May reenter the design activityMay reenter the design activity
Usually developed in parallelUsually developed in parallel Problems cutting across sub-system boundaries are Problems cutting across sub-system boundaries are
encounteredencounteredA system modification must be made - changes in the A system modification must be made - changes in the software requirementssoftware requirements
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2.2.5 Systems integration2.2.5 Systems integration
Putting hardware, software and people together to make Putting hardware, software and people together to make a complete systema complete systemTwo approachesTwo approaches
A ‘big bang’ approachA ‘big bang’ approachAll sub-systems are integrated at the same timeAll sub-systems are integrated at the same time
An incremental integration approachAn incremental integration approachSub-systems are integrated one at a timeSub-systems are integrated one at a timeBest approachBest approach
Impossible to finish all sub-systems at the same timeImpossible to finish all sub-systems at the same time Reduce the cost of error locationReduce the cost of error location
An extensive program of system testingAn extensive program of system testing The interfaces between componentsThe interfaces between components The behavior of the system as a wholeThe behavior of the system as a whole
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2.2.6 System installation2.2.6 System installation
After completion, the system has to be installed After completion, the system has to be installed in the customer’s environmentin the customer’s environment Environmental assumptions may be incorrect;Environmental assumptions may be incorrect; May be human resistance to the introduction of May be human resistance to the introduction of
a new systema new system System may have to coexist with alternative System may have to coexist with alternative
systems for some timesystems for some time May be physical installation problems (e.g. May be physical installation problems (e.g.
cabling problems)cabling problems) Operator training has to be identifiedOperator training has to be identified
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2.2.7 System evolution2.2.7 System evolution
Complex systems have a very long lifetimeComplex systems have a very long lifetime To correct errorsTo correct errors To implement new requirementsTo implement new requirements
Evolution is inherently costlyEvolution is inherently costly Changes must be analyzed from a technical and business Changes must be analyzed from a technical and business
perspectiveperspective Sub-systems interact so unanticipated problems can ariseSub-systems interact so unanticipated problems can arise There is rarely a rationale for original design decisionsThere is rarely a rationale for original design decisions System structure is corrupted as changes are made to itSystem structure is corrupted as changes are made to it
Existing systems which must be maintained are Existing systems which must be maintained are sometimes called sometimes called legacy systemslegacy systems..
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2.2.8 System decommissioning2.2.8 System decommissioning
Taking the system out of service after its useful Taking the system out of service after its useful operation lifetimeoperation lifetime May require removal of materials (e.g. dangerous May require removal of materials (e.g. dangerous
chemicals) which pollute the environmentchemicals) which pollute the environmentShould be planned for in the system design by encapsulationShould be planned for in the system design by encapsulation
May require data to be restructured and converted to May require data to be restructured and converted to be used in some other systembe used in some other system
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ContentsContents
2.1 Emergent system properties2.1 Emergent system properties
2.2 System engineering2.2 System engineering
2.3 Organizations, people and computer systems2.3 Organizations, people and computer systems
2.4 Legacy systems2.4 Legacy systems
2.5 Exercises2.5 Exercises
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Organizations, people andOrganizations, people andcomputer systemscomputer systems
Socio-technical systemsSocio-technical systems Enterprise systems to deliver some Enterprise systems to deliver some
organizational/business goalorganizational/business goal Embedded in an organizational environmentEmbedded in an organizational environment
Need to understand its organizational environmentNeed to understand its organizational environment
Human and organizational factorsHuman and organizational factors Process changesProcess changes
Require changes to the work processes? Require changes to the work processes? Job changesJob changes
De-skill the users or change the way they work? De-skill the users or change the way they work? Organizational changesOrganizational changes
Change the political power structure in an organization?Change the political power structure in an organization?
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2.3.1 Organizational processes2.3.1 Organizational processes
The development process interacts withThe development process interacts with The The procurementprocurement process process
Making decisions aboutMaking decisions about The best way to acquire a systemThe best way to acquire a system The best suppliersThe best suppliers
The The operationaloperational process processUsing the system for its intended purposeUsing the system for its intended purpose
Procurementprocess
Operationalprocess
Developmentprocess
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The system procurement processThe system procurement process
Large complex systemsLarge complex systems a mixture of off-the-shelf and specially built a mixture of off-the-shelf and specially built
componentscomponents
Important pointsImportant points Off-the-shelf components do not usually match Off-the-shelf components do not usually match
requirements exactlyrequirements exactlyMay have to modify the requirementsMay have to modify the requirements
The specification of requirements acts as the basis of The specification of requirements acts as the basis of a contract for a specially built systema contract for a specially built system
A legal and technical documentA legal and technical document After a contractor has been selected, there is a After a contractor has been selected, there is a
contract negotiation periodcontract negotiation period
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The system procurement processThe system procurement process
Choosesupplier
Issue requestfor bids
Choosesystem
Adaptrequirements
Survey market forexisting systems
Let contract fordevelopment
Negotiatecontract
Selecttender
Issue requestto tender
Off-the-shelfsystem available
Custom systemrequired
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ContentsContents
2.1 Emergent system properties2.1 Emergent system properties
2.2 System engineering2.2 System engineering
2.3 Organizations, people and computer systems2.3 Organizations, people and computer systems
2.4 Legacy systems2.4 Legacy systems
2.5 Exercises2.5 Exercises
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Legacy systemsLegacy systems
Large computer-based systems usually have a Large computer-based systems usually have a long lifetimelong lifetime 20 years for military systems20 years for military systems Air traffic control (ATC) relies on software and Air traffic control (ATC) relies on software and
operational processes that were developed in the operational processes that were developed in the 1960s and 1970s1960s and 1970s
Too expensive and too risky to discard such business Too expensive and too risky to discard such business critical systems after a few years of usecritical systems after a few years of use
Their development continues throughout their Their development continues throughout their life with changeslife with changes RequirementsRequirements Operating platformsOperating platforms
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Legacy systemsLegacy systems
Socio-technical computer-based systems that Socio-technical computer-based systems that developed in the past using older or obsolete developed in the past using older or obsolete technologytechnology Hardware and softwareHardware and software Legacy processes and proceduresLegacy processes and procedures
Often business-critical systemsOften business-critical systems Too risky to replace themToo risky to replace them e.g. bank customer accounting systeme.g. bank customer accounting system e.g. aircraft maintenance systeme.g. aircraft maintenance system
Constrain new business processes and Constrain new business processes and consume a high proportion of company budgetsconsume a high proportion of company budgets
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Legacy system componentsLegacy system components
Systemhardware
Businessprocesses
Applicationsoftware
Business policiesand rules
Support software
Application data
ConstrainsUsesUsesRuns-onRuns-on
Embedsknowledge of
Uses
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Layered model of a legacy systemLayered model of a legacy system
Socio-technical system
Hardware
Support software
Application software
Business processes
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ContentsContents
2.1 Emergent system properties2.1 Emergent system properties
2.2 System engineering2.2 System engineering
2.3 Organizations, people and computer systems2.3 Organizations, people and computer systems
2.4 Legacy systems2.4 Legacy systems
2.5 Exercises2.5 Exercises
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ExercisesExercises
2.42.4
2.62.6
The EndThe End