1. Software Engineering Chapter 2 Socio-technical systems Ku-Yaw Chang canseco@mail.dyu.edu.tw Assistant Professor Department of Computer Science and Information Engineering Da-Yeh University

2. 2Ku-Yaw ChangSocio-technical Systems Objectives Know what is meant by socio-technical system and understand the difference between a technical computer- based system and a socio-technical system Have been introduced to the concept of emergent system properties such as reliability, performance, safety and security Understand the activities that are involved in the systems engineering process Understand why the organizational context of a system affects its design and use Know what is meant by a ‘legacy system’, and why these systems are often critical to the operation of many business

3. 3Ku-Yaw ChangSocio-technical Systems Preamble What is a system? A purposeful collection of inter-related components that work together to achieve some objective. A purposeful collection of inter-related components that work together to achieve some objective. A system may include software, mechanical, electrical and electronic hardware and be operated by people. A system may include software, mechanical, electrical and electronic hardware and be operated by people. System components are dependent on other system components System components are dependent on other system components The properties and behavior of system components are inextricably inter-mingled The properties and behavior of system components are inextricably inter-mingled

4. 4Ku-Yaw ChangSocio-technical Systems Preamble System categories Technical computer-based systems Technical computer-based systems Systems that include hardware and software but 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 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 organizational policies and rules.

5. 5Ku-Yaw ChangSocio-technical Systems Preamble Socio-technical system characteristics Emergent properties Emergent properties Properties of the system of a whole that depend on the system components and their relationships. Non-deterministic Non-deterministic They do not always produce the same output when presented with the same input because the system’s behavior is partially dependent on human operators. Complex relationships with organizational objectives Complex relationships with organizational objectives The extent to which the system supports organizational objectives does not just depend on the system itself.

6. 6Ku-Yaw ChangSocio-technical Systems Contents 2.1 Emergent system properties 2.2 System engineering 2.3 Organizations, people and computer systems 2.4 Legacy systems 2.5 Exercises

7. 7Ku-Yaw ChangSocio-technical Systems 2.1 Emergent system properties Properties of the system as a whole rather than properties that can be derived from the properties of components of a system a consequence of the relationships between system components a consequence of the relationships between system components only be assessed and measured once the components have been integrated into a system only be assessed and measured once the components have been integrated into a system

8. 8Ku-Yaw ChangSocio-technical Systems Examples of emergent properties Volume Total space occupied Total space occupiedReliability Depends on component reliability Depends on component reliability Unexpected interactions cause new failure Unexpected interactions cause new failureSecurity Ability to resist attack Ability to resist attackReparability How easy to fix a problem How easy to fix a problemUsability How easy to use the system How easy to use the system

9. 9Ku-Yaw ChangSocio-technical Systems Types of emergent properties Functional emergent properties All the parts of a system work together to achieve some objective All the parts of a system work together to achieve some objective a bicycle has the functional property of being a transportation device once it has been assembled from its components. Non-functional emergent properties Relate to the behavior of the system in its operational environment Relate to the behavior of the system in its operational environment Reliability, performance, safety, and security Critical for computer-based systems Critical for computer-based systems Failure to achieve some minimal defined level in these properties may make the system unusable.

10. 10Ku-Yaw ChangSocio-technical Systems Complexity of emergent properties Consider the property of system reliability Because of component inter-dependencies, faults can be propagated through the system. Because of component inter-dependencies, faults can be propagated through the system. System failures often occur because of unforeseen inter-relationships between components. System failures often occur because of unforeseen inter-relationships between components. It is probably impossible to anticipate all possible component relationships. It is probably impossible to anticipate all possible component relationships. Software reliability measures may give a false picture of the system reliability. Software reliability measures may give a false picture of the system reliability.

11. 11Ku-Yaw ChangSocio-technical Systems Influences on reliability Hardware reliability What is the probability of a hardware component failing and how long does it take to repair that component? 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 an incorrect output. How likely is it that a software component will produce an incorrect output. Software failure is usually distinct from hardware failure in that software does not wear out. 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? How likely is it that the operator of a system will make an error?

12. 12Ku-Yaw ChangSocio-technical Systems 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.

13. 13Ku-Yaw ChangSocio-technical Systems 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; Safety - the system should not behave in an unsafe way; Security - the system should not permit unauthorised use. Security - the system should not permit unauthorised use. Measuring or assessing these properties is very hard Knowing a system is insecure only when someone breaks into it Knowing a system is insecure only when someone breaks into it

14. 14Ku-Yaw ChangSocio-technical Systems Contents 2.1 Emergent system properties 2.2 System engineering 2.3 Organizations, people and computer systems 2.4 Legacy systems 2.5 Exercises

15. 15Ku-Yaw ChangSocio-technical Systems System engineering The activity of specifying, designing, implementing, validating, deploying and maintaining socio-technical systems Concerned with Software Software Hardware Hardware System’s interactions with users and its environment System’s interactions with users and its environment

16. 16Ku-Yaw ChangSocio-technical Systems The systems engineering process

17. 17Ku-Yaw ChangSocio-technical Systems Important distinctions Limited scope for rework during system development Little scope for iteration between phases because hardware changes are very expensive Little scope for iteration between phases because hardware changes are very expensive Interdisciplinary involvement Inevitably involve engineers from different disciplines who must work together Inevitably involve engineers from different disciplines who must work together Different engineers use different terminology and conventions Different engineers use different terminology and conventions

18. 18Ku-Yaw ChangSocio-technical Systems Inter-disciplinary involvement

19. 19Ku-Yaw ChangSocio-technical Systems 2.2.1 System requirements definition Specify What the system should do (its functions) What the system should do (its functions) Essential and desirable system properties Essential and desirable system properties Involve consultations with system customers/end-users Derive three types of requirement Abstract functional requirements Abstract functional requirements Basic functions at an abstract level System properties System properties Non-functional emergent system properties Characteristics that the system must no exhibit Characteristics that the system must no exhibit Must not do vs. should do e.g. Too much information should not be presented to the controller e.g. Too much information should not be presented to the controller

20. 20Ku-Yaw ChangSocio-technical Systems 2.2.1 System requirements definition To establish a set of overall objectives that the system should meet Functional objectives Functional objectives To provide a fire and intruder alarm system for the building which will provide internal and external warning of fire or unauthorized intrusion. Organizational objectives Organizational objectives To ensure that the normal functioning of work carried out in the building is not seriously disrupted by events such as fire and unauthorized intrusion.

21. 21Ku-Yaw ChangSocio-technical Systems 2.2.1 System requirements definition Complex systems are usually developed to address wicked problems So many related entities that there is no definitive problem specification So many related entities that there is no definitive problem specification An extreme example An extreme example Earthquake planning

22. 22Ku-Yaw ChangSocio-technical Systems 2.2.2 System design How the system functionality is to be provided by the components of the system Partition requirements Partition requirements Analyze requirements and organize them into related groups Identify sub-systems Identify sub-systems Individually or collectively meet the requirements Assign requirements to sub-systems Assign requirements to sub-systems Never a clean match between requirements partitions and identified sub-systems Specify sub-system functionality Specify sub-system functionality Define sub-system interfaces Define sub-system interfaces

23. 23Ku-Yaw ChangSocio-technical Systems The system design process Double-ended arrows A lot of feedback and iteration from one stage to another in the design process A lot of feedback and iteration from one stage to another in the design process

24. 24Ku-Yaw ChangSocio-technical Systems Requirements and design Requirements affect design decisions and vice versa In practice, the are inextricably linked In practice, the are inextricably linked Constraints posed by the existing systems may Limit design choices Limit design choices These choices may be specified in the requirements These choices may be specified in the requirements Initial design may be necessary to structure the requirements. Initial design may be necessary to structure the requirements. As you do design, you learn more about the requirements.

25. 25Ku-Yaw ChangSocio-technical Systems Spiral model of requirements/design

26. 26Ku-Yaw ChangSocio-technical Systems 2.2.3 System modeling An architectural model A set of components (sub-systems) and their relationships A set of components (sub-systems) and their relationships An abstract view of the sub-systems making up a system An abstract view of the sub-systems making up a system More appropriate to classify sub-systems according to their function More appropriate to classify sub-systems according to their function Before making decisions about hardware/software trade-offs Illustrated graphically and presented as a block diagram Illustrated graphically and presented as a block diagram Be supplemented by brief descriptions of each subsystem May be used for all sizes of system

27. 27Ku-Yaw ChangSocio-technical Systems A simple burglar alarm system

28. 28Ku-Yaw ChangSocio-technical Systems Sub-system description

29. 29Ku-Yaw ChangSocio-technical Systems ATC system architecture

30. 30Ku-Yaw ChangSocio-technical Systems 2.2.4 Sub-system development The implementation may involve starting Another system engineering process Another system engineering process A software process A software process Commercial off-the-shelf (COTS) systems are bought for integration into the system May reenter the design activity May reenter the design activity Usually developed in parallel Problems cutting across sub-system boundaries are encountered Problems cutting across sub-system boundaries are encountered A system modification must be made - changes in the software requirements

31. 31Ku-Yaw ChangSocio-technical Systems 2.2.5 Systems integration Putting hardware, software and people together to make a complete system Two approaches A ‘big bang’ approach A ‘big bang’ approach All sub-systems are integrated at the same time An incremental integration approach An incremental integration approach Sub-systems are integrated one at a time Best approach Impossible to finish all sub-systems at the same time Impossible to finish all sub-systems at the same time Reduce the cost of error location Reduce the cost of error location An extensive program of system testing The interfaces between components The interfaces between components The behavior of the system as a whole The behavior of the system as a whole

32. 32Ku-Yaw ChangSocio-technical Systems 2.2.6 System installation After completion, the system has to be installed in the customer’s environment Environmental assumptions may be incorrect; Environmental assumptions may be incorrect; May be human resistance to the introduction of a new system May be human resistance to the introduction of a new system System may have to coexist with alternative systems for some time System may have to coexist with alternative systems for some time May be physical installation problems (e.g. cabling problems) May be physical installation problems (e.g. cabling problems) Operator training has to be identified Operator training has to be identified

33. 33Ku-Yaw ChangSocio-technical Systems 2.2.7 System evolution Complex systems have a very long lifetime To correct errors To correct errors To implement new requirements To implement new requirements Evolution is inherently costly Changes must be analyzed from a technical and business perspective Changes must be analyzed from a technical and business perspective Sub-systems interact so unanticipated problems can arise Sub-systems interact so unanticipated problems can arise There is rarely a rationale for original design decisions There is rarely a rationale for original design decisions System structure is corrupted as changes are made to it System structure is corrupted as changes are made to it Existing systems which must be maintained are sometimes called legacy systems.

34. 34Ku-Yaw ChangSocio-technical Systems 2.2.8 System decommissioning Taking the system out of service after its useful operation lifetime May require removal of materials (e.g. dangerous chemicals) which pollute the environment May require removal of materials (e.g. dangerous chemicals) which pollute the environment Should be planned for in the system design by encapsulation May require data to be restructured and converted to be used in some other system May require data to be restructured and converted to be used in some other system

35. 35Ku-Yaw ChangSocio-technical Systems Contents 2.1 Emergent system properties 2.2 System engineering 2.3 Organizations, people and computer systems 2.4 Legacy systems 2.5 Exercises

36. 36Ku-Yaw ChangSocio-technical Systems Organizations, people and computer systems Socio-technical systems Enterprise systems to deliver some organizational/business goal Enterprise systems to deliver some organizational/business goal Embedded in an organizational environment Embedded in an organizational environment Need to understand its organizational environment Human and organizational factors Process changes Process changes Require changes to the work processes? Job changes Job changes De-skill the users or change the way they work? Organizational changes Organizational changes Change the political power structure in an organization?

37. 37Ku-Yaw ChangSocio-technical Systems 2.3.1 Organizational processes The development process interacts with The procurement process The procurement process Making decisions about The best way to acquire a system The best way to acquire a system The best suppliers The best suppliers The operational process The operational process Using the system for its intended purpose

38. 38Ku-Yaw ChangSocio-technical Systems The system procurement process Large complex systems a mixture of off-the-shelf and specially built components a mixture of off-the-shelf and specially built components Important points Off-the-shelf components do not usually match requirements exactly Off-the-shelf components do not usually match requirements exactly May have to modify the requirements The specification of requirements acts as the basis of a contract for a specially built system The specification of requirements acts as the basis of a contract for a specially built system A legal and technical document After a contractor has been selected, there is a contract negotiation period After a contractor has been selected, there is a contract negotiation period

39. 39Ku-Yaw ChangSocio-technical Systems The system procurement process

40. 40Ku-Yaw ChangSocio-technical Systems Contents 2.1 Emergent system properties 2.2 System engineering 2.3 Organizations, people and computer systems 2.4 Legacy systems 2.5 Exercises

41. 41Ku-Yaw ChangSocio-technical Systems Legacy systems Large computer-based systems usually have a long lifetime 20 years for military systems 20 years for military systems Air traffic control (ATC) relies on software and operational processes that were developed in the 1960s and 1970s Air traffic control (ATC) relies on software and operational processes that were developed in the 1960s and 1970s Too expensive and too risky to discard such business critical systems after a few years of use Too expensive and too risky to discard such business critical systems after a few years of use Their development continues throughout their life with changes Requirements Requirements Operating platforms Operating platforms

42. 42Ku-Yaw ChangSocio-technical Systems Legacy systems Socio-technical computer-based systems that developed in the past using older or obsolete technology Hardware and software Hardware and software Legacy processes and procedures Legacy processes and procedures Often business-critical systems Too risky to replace them Too risky to replace them e.g. bank customer accounting system e.g. bank customer accounting system e.g. aircraft maintenance system e.g. aircraft maintenance system Constrain new business processes and consume a high proportion of company budgets

43. 43Ku-Yaw ChangSocio-technical Systems Legacy system components

44. 44Ku-Yaw ChangSocio-technical Systems Layered model of a legacy system

45. 45Ku-Yaw ChangSocio-technical Systems Contents 2.1 Emergent system properties 2.2 System engineering 2.3 Organizations, people and computer systems 2.4 Legacy systems 2.5 Exercises

46. 46Ku-Yaw ChangSocio-technical Systems Exercises 2.42.6

47. The End