Chapt er 6
Syst em Engineer ing

Software Engineering: A Practitioner’s Approach, 6th edition
by Roger S. Pressman

1
Syst em Engineer ing
 Software Engineering occurs as a
consequence of a process called system
engineering.
 System engin...
The
Hier ar chy
Business or
Product Dom
ain

World view

Dom
ain of interest

Dom
ain view

System elem
ent

Elem
ent view...
Pr oduct Engineer ing
The complete
product

System analysis
(World view)

capabilities

hardware

Component
engineering
( ...
Syst em Engineer ing Cont .
 Definition of Computer based system: A
set or arrangement of elements that are
organized to ...
Chapt er 7
Requir ement s Engineer ing

Software Engineering: A Practitioner’s Approach, 6th edition
by Roger S. Pressman
...
Requir ement s Engineer ing
 Requirement: A

function, constraint or other property
that the system must provide to fill ...
Requir ement s Engineer ing
Requirement engineering process is accomplished through the
execution of seven distinct functi...
I ncept ion
 Ask “context-free” questions











Who is behind the request for this work?
Who will use the ...
Get t ing Requir ement s Right
 “The hardest single part of building a software system is
deciding what to build. No part...
Elicit ing Requir ement s
 Why is it so difficult to clearly understand what the customer wants?
 Problems of Scope
 Th...
Elabor at ion, Negot iat ion
 Information obtained from the customer
during inception and elicitation is expanded
and ref...
Specif icat ion, Validat ion
 Specification means different things to different
people.
 Specification can be a written ...
Requir ement s Management
 Requirement management is a set of
activities that help the project team identify,
control, an...
I nit iat ing t he Requir ement s
Engineer ing Pr ocess
 To get the project started in a way that
will keep it moving for...
Elicit ing Requir ement s
 Various approaches can be taken into
consideration like
•
•
•
•

Collaborative Requirements Ga...
What ar e t he basic guidelines f or conduct ing
a collabor at ive r equir ement s gat her ing
meet ing?
 Meetings are co...
Qualit y Funct ion Deployment
 Quality function deployment is a technique that
translates the needs of the customer into ...
User Scenar ios
 It is difficult to move into more technical
software engineering activities until the
software team unde...
Elicit at ion Wor k
Pr oduct s

 What information is produced as a consequence of
requirements gathering?
•
•
•
•
•

Stat...
Developing Use-Cases
 A use-case scenario is a story about how someone or something
external to the software (known as an...
Use-Case Diagr am

22
Element s of t he Analysis
Model
 Scenario-based elements
 Use-case—How external actors interact with the
system (use-ca...
Act ivit y Diagr am f or RE

24
Class Diagr am

25
St at e Diagr am

26
Analysis Pat t er ns
Pattern name: Captures the essence of the pattern.
Intent: What the pattern accomplishes or represent...
Negot iat ing Requir ement s
 Identify the key stakeholders
 These are the people who will be involved in the
negotiatio...
Validat ing Requir ement s
 Is each requirement consistent with the objective of the
system?
 Have all requirements been...
Example CRG Meet ing
 First CRG meeting of the SafeHome project.
 After Q&A session (inception meeting), stakeholders wr...
Example CRG Meet ing
 Our research indicates that the market for home management
systems is growing at a rate of 40 perce...
Example CRG Meet ing
 Objects – control panel, smoke detectors, window and door
sensors, motion detectors, an alarm, an e...
Example CRG Meet ing
 Mini-specification for Control Panel
 The Control Panel is a wall-mounted unit
that is approximate...
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Software engg. pressman_ch-6 & 7

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Software engg. pressman_ch-6 & 7

  1. 1. Chapt er 6 Syst em Engineer ing Software Engineering: A Practitioner’s Approach, 6th edition by Roger S. Pressman 1
  2. 2. Syst em Engineer ing  Software Engineering occurs as a consequence of a process called system engineering.  System engineering process takes on different forms depending on the application domain in which it is applied. 1 Business Process engineering 2 Product engineering 2
  3. 3. The Hier ar chy Business or Product Dom ain World view Dom ain of interest Dom ain view System elem ent Elem ent view Detailed view 3
  4. 4. Pr oduct Engineer ing The complete product System analysis (World view) capabilities hardware Component engineering ( Domain view) software P rocessing requirement data function behavior Analysis & Design M odeling (Element view) program component Software E ngineering Construction & Integration (Detailed view) 4
  5. 5. Syst em Engineer ing Cont .  Definition of Computer based system: A set or arrangement of elements that are organized to accomplish some predefined goal by processing information.  Elements of computer based system: 1. Software 2. Hardware 3. People 4. Documentation 5. Database 6. Procedures 5
  6. 6. Chapt er 7 Requir ement s Engineer ing Software Engineering: A Practitioner’s Approach, 6th edition by Roger S. Pressman 6
  7. 7. Requir ement s Engineer ing  Requirement: A function, constraint or other property that the system must provide to fill the needs of the system’s intended user(s)  Engineering: implies that systematic and repeatable techniques should be used to ensure that system requirements are complete, consistent, relevant . . . etc.  Requirement Engineering covers all of the activities involved in discovering, documenting, and maintaining a set of requirements for a system.  RE means that requirements for a product are defined, managed and tested systematically 7
  8. 8. Requir ement s Engineer ing Requirement engineering process is accomplished through the execution of seven distinct functions: Inception—Establish a basic understanding of the problem and the nature of the solution. Elicitation—Draw out the requirements from stakeholders. Elaboration—Create an analysis model that represents information, functional, and behavioral aspects of the requirements. Negotiation—Agree on a deliverable system that is realistic for developers and customers. Specification—Describe the requirements formally or informally. Validation—Review the requirement specification for errors, ambiguities, omissions, and conflicts. 8 Requirements management—Manage changing requirements.
  9. 9. I ncept ion  Ask “context-free” questions           Who is behind the request for this work? Who will use the solution (product/system)? What will be the economic benefits? How would you characterize “good” output from the system? What problems does this solution address? What environment will the product be used in? Are you the right person to answer these questions? Are these question relevant? Can anyone else provide additional information? Should I be asking you anything else? 9
  10. 10. Get t ing Requir ement s Right  “The hardest single part of building a software system is deciding what to build. No part of the work so cripples the resulting system if done wrong. No other part is more difficult to rectify later.” —Fred Brooks  “The seeds of major software disasters are usually sown within the first three months of commencing the software project.” —Capers Jones  “We spend a lot of time—the majority of project effort—not implementing or testing, but trying to decide what to build.” —Brian Lawrence 10
  11. 11. Elicit ing Requir ement s  Why is it so difficult to clearly understand what the customer wants?  Problems of Scope  The boundary of the system is ill-defined.  Customers/users specify unnecessary technical detail that may confuse rather than clarify objectives.  Problems of understanding  Customers are not completely sure of what is needed.  Customers have a poor understanding of the capabilities and limitations of the computing environment.  Customers don’t have a full understanding of their problem domain.  Customers have trouble communicating needs to the system engineer.  Customers omit detail that is believed to be obvious.  Customers specify requirements that conflict with other requirements.  Customers specify requirements that are ambiguous or untestable.  Problems of Volatility  Requirements change over time. 11
  12. 12. Elabor at ion, Negot iat ion  Information obtained from the customer during inception and elicitation is expanded and refined during elaboration.  The end result of elaboration is an analysis model that defines the informational, functional, and behavioral domain of the problem.  Requirement engineer reconcile the conflicts if any through the process of negotiation. 12
  13. 13. Specif icat ion, Validat ion  Specification means different things to different people.  Specification can be a written document, a set of graphical models, a formal mathematical model, a collection of usage scenarios, a prototype, or any combination of these.  Work products produced as a consequence of requirements engineering are assessed for quality during validation step.  Primary requirement validation mechanism is the formal technical review. 13
  14. 14. Requir ement s Management  Requirement management is a set of activities that help the project team identify, control, and track requirements and changes to requirements at any time as the project proceeds. 14
  15. 15. I nit iat ing t he Requir ement s Engineer ing Pr ocess  To get the project started in a way that will keep it moving forward toward a successful solution.  Identifying the stakeholders  Recognizing Multiple Viewpoints  Working toward Collaboration  Asking the first questions 15
  16. 16. Elicit ing Requir ement s  Various approaches can be taken into consideration like • • • • Collaborative Requirements Gathering Quality Function Deployment User Scenarios Elicitation Work Products 16
  17. 17. What ar e t he basic guidelines f or conduct ing a collabor at ive r equir ement s gat her ing meet ing?  Meetings are conducted and attended by all interested stakeholders.  Rules for preparation and participation are established.  Agenda should be formal enough to cover all important points, but informal enough to encourage the free flow of ideas.  A facilitator (can be customer, a developer, or an outsider) controls the meeting.  A definition mechanism (blackboard, flip charts, etc.) is used.  During the meeting:      The problem is identified. Elements of the solution are proposed. Different approaches are negotiated. A preliminary set of solution requirements are obtained. The atmosphere is collaborative and non-threatening. 17
  18. 18. Qualit y Funct ion Deployment  Quality function deployment is a technique that translates the needs of the customer into technical requirements for software.  QFD identifies three types of requirements  Normal requirements: reflect objectives and goals stated for a product  Expected requirements: are implicit to the product or system and may be so fundamental that the customer does not explicitly state them.  Exciting requirements: reflect features that go beyond the customer’s expectations and prove to be very satisfying when present. 18
  19. 19. User Scenar ios  It is difficult to move into more technical software engineering activities until the software team understands how these functions and features will be used by different classes of end users.  To accomplish this, developers and users create a set of scenarios often called use-cases. 19
  20. 20. Elicit at ion Wor k Pr oduct s  What information is produced as a consequence of requirements gathering? • • • • • Statement of need and feasibility. Bounded Statement of scope. List of participants in requirements elicitation. Description of the system’s technical environment. List of requirements and associated domain constraints. • List of usage scenarios. • Any prototypes developed to refine requirements. 20
  21. 21. Developing Use-Cases  A use-case scenario is a story about how someone or something external to the software (known as an actor) interacts with the system.  Each scenario answers the following questions: • Who is the primary actor, the secondary actor(s)?        What are the actor’s goals? What preconditions should exist before the story begins? What main tasks or functions are performed by the actor? What exceptions might be considered as the story is described? What variations in the actor’s interaction are possible? What system information will the actor acquire, produce, or change? Will the actor have to inform the system about changes in the external environment?  What information does the actor desire from the system?  Does the actor wish to be informed about unexpected changes? 21
  22. 22. Use-Case Diagr am 22
  23. 23. Element s of t he Analysis Model  Scenario-based elements  Use-case—How external actors interact with the system (use-case diagrams; detailed templates)  Functional—How software functions are processed in the system (flow charts; activity diagrams)  Class-based elements  The various system objects (obtained from scenarios) including their attributes and functions (class diagram)  Behavioral elements  How the system behaves in response to different events (state diagram)  Flow-oriented elements  How information is transformed as if flows through the system (data flow diagram) 23
  24. 24. Act ivit y Diagr am f or RE 24
  25. 25. Class Diagr am 25
  26. 26. St at e Diagr am 26
  27. 27. Analysis Pat t er ns Pattern name: Captures the essence of the pattern. Intent: What the pattern accomplishes or represents. Motivation: A scenario that illustrates how the pattern solves a problem. Forces and context: External issues (forces) that affect how the pattern is used, and external issues resolved when the pattern is applied. Solution: How the pattern is applied to solve the problem; emphasizes structural and behavioral issues. Consequences: What happens when the pattern is applied; what trade-offs exist during its application. Design: How the pattern can be achieved via known design patterns. Known uses: Examples of uses within actual systems. Related patterns: Patterns related to the named pattern because (1) they are commonly used with the named pattern; (2) they are structurally similar to the named pattern; (3) they are a variation of the named pattern. 27
  28. 28. Negot iat ing Requir ement s  Identify the key stakeholders  These are the people who will be involved in the negotiation  Determine each of the stakeholders “win conditions”  Win conditions are not always obvious  Negotiate  Work toward a set of requirements that lead to “win-win” 28
  29. 29. Validat ing Requir ement s  Is each requirement consistent with the objective of the system?  Have all requirements been specified at the proper level of abstraction?  Is the requirement really necessary?  Is each requirement bounded and unambiguous?  Does each requirement have attribution?  Do any requirements conflict with other requirements?  Is each requirement achievable in the system’s technical environment?  Is each requirement testable, once implemented?  Does the model reflect the system’s information, function and behavior? 29 
  30. 30. Example CRG Meet ing  First CRG meeting of the SafeHome project.  After Q&A session (inception meeting), stakeholders write a two page product request, which is delivered to those attending the first CRG meeting.  Attendees are asked to make a rough list of objects, services, constraints, and performance criteria for the product.  At the meeting, a combined list is created in each topic.  Subgroups write mini-specifications for each list item.  Relevant features in mini-specifications are added to the list. 30
  31. 31. Example CRG Meet ing  Our research indicates that the market for home management systems is growing at a rate of 40 percent per year. The first SafeHome function we bring to market should be the home security function. Most people are familiar with “alarm systems” so this would be an easy sell.  The home security function would protect against and/or recognize a variety of undesirable “situations” such as illegal entry, fire, flooding, carbon monoxide levels, and others. It’ll use our wireless sensors to detect each situation, can be programmed by the homeowner, and will automatically telephone a monitoring agency when a situation is detected. 31
  32. 32. Example CRG Meet ing  Objects – control panel, smoke detectors, window and door sensors, motion detectors, an alarm, an event (sensor has been activated), a display, a PC, telephone numbers, a telephone call, …  Services – configuring the system, setting the alarm, monitoring the sensors, dialing the phone, programming the control panel, reading the display, …  Constraints – System must recognize when sensors are not operating, must be user friendly, must interface directly to a standard phone line, …  Performance criteria – Sensor event should be recognized within one second, an event priority scheme should be implemented, … 32
  33. 33. Example CRG Meet ing  Mini-specification for Control Panel  The Control Panel is a wall-mounted unit that is approximately 9 x 5 inches in size. The control panel has wireless connectivity to sensors and a PC. User interaction occurs through a keypad containing 12 keys. A 2 x 2 inch LCD display provides user feedback. Software provides interactive prompts, echo, and similar functions. 33

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