3. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 7/e
3
Inception—ask a set of questions that establish …
– basic understanding of the problem
– the people who want a solution
– the nature of the solution that is desired, and
– the effectiveness of preliminary communication and collaboration
between the customer and the developer
Elicitation—elicit requirements from all stakeholders
Elaboration—create an analysis model that identifies
data, function and behavioral requirements
Negotiation—agree on a deliverable system that is
realistic for developers and customers
Requirements Engineering-I
4. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 7/e
4
Requirements Engineering-II
Specification—can be any one (or more) of the following:
– A written document
– A set of models
– A formal mathematical
– A collection of user scenarios (use-cases)
– A prototype
Validation—a review mechanism that looks for
– errors in content or interpretation
– areas where clarification may be required
– missing information
– inconsistencies (a major problem when large products or systems
are engineered)
– conflicting or unrealistic (unachievable) requirements.
Requirements management
5. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 7/e
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Inception
Identify stakeholders
– “who else do you think I should talk to?”
Recognize multiple points of view
Work toward collaboration
The first questions
– Who is behind the request for this work?
– Who will use the solution?
– What will be the economic benefit of a
successful solution
– Is there another source for the solution that
you need?
6. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 7/e
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Eliciting Requirements
meetings are conducted and attended by both software
engineers and customers
rules for preparation and participation are established
an agenda is suggested
a "facilitator" (can be a customer, a developer, or an
outsider) controls the meeting
a "definition mechanism" (can be work sheets, flip charts, or
wall stickers or an electronic bulletin board, chat room or
virtual forum) is used
the goal is
– to identify the problem
– propose elements of the solution
– negotiate different approaches, and
– specify a preliminary set of solution requirements
7. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 7/e
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Elicitation Work Products
a statement of need and feasibility.
a bounded statement of scope for the system or
product.
a list of customers, users, and other stakeholders who
participated in requirements elicitation
a description of the system’s technical environment.
a list of requirements (preferably organized by function)
and the domain constraints that apply to each.
a set of usage scenarios that provide insight into the
use of the system or product under different operating
conditions.
any prototypes developed to better define requirements.
8. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 7/e
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Building the Analysis Model
Elements of the analysis model
– Scenario-based elements
Functional—processing narratives for software
functions
Use-case—descriptions of the interaction between an
“actor” and the system
– Class-based elements
Implied by scenarios – class diagram
– Behavioral elements
State diagram
– Flow-oriented elements
Data flow diagram
9. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 7/e
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Use-Cases
A collection of user scenarios that describe the thread of usage of
a system
Each scenario is described from the point-of-view of an “actor”—a
person or device that interacts with the software in some way
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 extensions 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?
10. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 7/e
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Use-Case Diagram
homeowner
Arms/ disarms
system
Accesses system
via Internet
Reconfigures sensors
and related
system features
Responds to
alarm event
Encounters an
error condition
system
administrator
sensors
11. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 7/e
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Class Diagram
Sensor
name/id
type
location
area
characteristics
identify()
enable()
disable()
reconfigure()
From the SafeHome system …
12. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 7/e
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State Diagram
Reading
Commands
System status = “ready”
Display msg = “enter cmd”
Display status = steady
Entry/subsystems ready
Do: poll user input panel
Do: read user input
Do: interpret user input
State name
State variables
State activities
13. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 7/e
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Negotiating Requirements
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”
14. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 7/e
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Specifications - templates
Pressman:
http://www.processimpact.com/process_assets/srs_preview.pdf
Al Dawud – Illinois Institute of Technology:
http://www.cs.iit.edu/~oaldawud/CS487/project/requirement_spe
cification_document_template.htm
15. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 7/e
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Validating Requirements - I
Is each requirement consistent with the overall objective for
the system/product?
Have all requirements been specified at the proper level of
abstraction? That is, do some requirements provide a level
of technical detail that is inappropriate at this stage?
Is the requirement really necessary or does it represent an
add-on feature that may not be essential to the objective of
the system?
Is each requirement bounded and unambiguous?
Does each requirement have attribution? That is, is a source
(generally, a specific individual) noted for each requirement?
Do any requirements conflict with other requirements?
16. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 7/e
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Validating Requirements - II
Is each requirement achievable in the technical environment that
will house the system or product?
Is each requirement testable, once implemented?
Does the requirements model properly reflect the information,
function and behavior of the system to be built.
Has the requirements model been “partitioned” in a way that
exposes progressively more detailed information about the
system.
Have requirements patterns been used to simplify the
requirements model. Have all patterns been properly validated?
Are all patterns consistent with customer requirements?
