Object-Oriented and Classical Software Engineering Sixth Edition, WCB/McGraw-Hill, 2005 Stephen R. Schach [e-mail]

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Object-Oriented and Classical Software
Engineering Sixth Edition, WCB/McGraw-Hill,
2005Stephen R. Schachsrs_at_vuse.vanderbilt.edu
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CHAPTER 10 Unit C
REQUIREMENTS
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Continued from Unit 10B
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10.9 Continuing the Requirements Workflow The
Osbert Oglesby Case Study

• More details of each use case are needed now
• First consider use cases
• Buy a Painting, and
• Sell a Painting
• To refine the descriptions, determine what
  attributes need to be input when a painting is
  bought and when a painting is sold

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Attributes The Osbert Oglesby Case Study

• Attributes when buying a painting include
• Title of work, name of artist, date of painting,
  classification, medium, purchase price, name and
  address of seller
• (The complete list of attributes appears in the
  textbook in Figure 10.14 see over)
• Attributes when selling a painting are
• Date of sale, name of buyer, address of buyer,
  actual selling price

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Attributes The Osbert Oglesby Case Study (contd)
Figure 10.14
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Continuing the Requirements Workflow The Osbert
Oglesby Case Study

• Now the algorithm for computing the maximum
  purchase price is considered
• Classify the painting as a
• Masterpiece
• Masterwork, or
• Other painting 

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Maximum Price for a Masterpiece The Osbert
Oglesby Case Study

• Scan worldwide auction records over the past 25
  years for the most similar work by the same
  artist
• Use the auction purchase price of the most
  similar work as the base price
• The maximum purchase price is found by adding 8.5
  percent to the base price, compounded annually,
  for each year since that auction

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Maximum Price for a Masterwork The Osbert
Oglesby Case Study

• Compute the maximum purchase price as if the
  painting were a masterpiece by the same artist
• If the picture was painted in the 21st century,
  multiply this figure by 0.25
• Otherwise, multiply it by (21  c)/(22  c),
  where c is the century in which the work was
  painted (12 lt c lt 21)

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Maximum Price for an Other Painting The Osbert
Oglesby Case Study

• Measure the dimensions of the canvas
• The maximum purchase price is then given by the
  formula F ? A, where
• F is a constant for that artist (fashionability
  coefficient), and
• A is the area of the canvas in square centimeters
• If there is no fashionability coefficient for
  that artist, Osbert will not buy the painting

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Coefficient of Similarity The Osbert Oglesby
Case Study

• For a masterpiece or masterwork, the coefficient
  of similarity between two paintings is computed
  as follows
• Score 1 for a match on medium, otherwise 0
• Score 1 for a match on subject, otherwise 0
• Add these two numbers, multiply by the area of
  the smaller painting, and divide by the area of
  the larger
• The resulting number is the coefficient of
  similarity

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Coefficient of Similarity The Osbert Oglesby
Case Study (contd)

• If the coefficient of similarity between the
  painting under consideration and all the
  paintings in the file of auction data is zero,
  then Osbert will not buy that masterwork or
  masterpiece

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Fashionability Coefficients The Osbert Oglesby
Case Study

• The software product must include a list of
  artists and their corresponding F values
• The value of F can vary from month to month,
  depending on the current fashionability of an
  artist
• Osbert determines the value of F on the basis of
  his knowledge and experience
• He changes the value if prices for work by an
  artist increase or decrease

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Auction Data The Osbert Oglesby Case Study

• The software product must utilize information on
  worldwide auction sales of masterpieces over the
  past 25 years
• Each month Osbert receives a CD with updated
  worldwide auction prices these prices are never
  modified by Osbert

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Updated Use Cases The Osbert Oglesby Case Study

• The use-case descriptions must reflect this
  information
• The resulting description of the Buy a Painting
  use case is shown in Figure 10.14 (see 9 slides
  back)

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Updated Use Cases The Osbert Oglesby Case Study

• The description of the Sell a Painting use case

Figure 10.15
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Reports The Osbert Oglesby Case Study

• There are three reports
• Purchases during the past year
• Sales during the past year
• Detection of new trends
• Sample reports show Osberts needs are as follows
  (question marks in the first or last name of
  artist, or in the title or date of the work are
  to be included in all reports)

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Report of Purchases during the Past Year The
Osbert Oglesby Case Study

• A report is needed to display all the paintings
  purchased during the past year
• The average ratio of the purchase price to the
  suggested maximum price is required at the end of
  the report

Figure 10.16
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Report of Sales during the Past Year The Osbert
Oglesby Case Study

• A report is needed to display all the paintings
  sold during the past year
• The average ratio of the actual selling price to
  the target selling price is required at the end
  of the report

Figure 10.17
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Report of Trends during the Past Year The Osbert
Oglesby Case Study

• A report showing artists whose works Osbert has
  sold at a price that has exceeded the target
  selling price in every instance during the past
  year
• To appear in this report, at least two of the
  artists works must have been sold by Osbert
  during that period

Figure 10.18
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Updated Use Cases The Osbert Oglesby Case Study

• The updated description of the Produce a Report
  use case, incorporating the details listed
  earlier, appears in Figure 10.19 (see over)

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Updated Use Cases The Osbert Oglesby Case Study
(contd)
Figure 10.19
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10.10 The Test Workflow The Osbert Oglesby Case
Study

• There is a serious omission
• The use case for updating a fashionability
  coefficient has been overlooked
• Missing use case Update a Fashionability
  Coefficient

Figure 10.20
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The Test Workflow The Osbert Oglesby Case Study
(contd)

• The description of the use case Update a
  Fashionability Coefficient

Figure 10.21
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Second Iteration of the Use-Case Diagram The
Osbert Oglesby Case Study

• Incorporate all four use cases

Figure 10.22
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The Test Workflow The Osbert Oglesby Case Study
(contd)

• A fault was detected
• There was a missing use case
• The existing artifacts did not need to be changed
• Two additional artifacts had to be added
• A use case, and
• Its description

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The Test Workflow The Osbert Oglesby Case Study
(contd)

• The Unified Process is iterative and incremental
• Members of the development team must always be
  aware that changes and extensions to the current
  version of the software product may have to made
  at any time

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10.11 The Classical Requirements Phase

• There is no such thing as object-oriented
  requirements
• The requirements workflow has nothing to do with
  how the product is to be built
• However, the approach presented in this chapter
  is
• Model oriented, and therefore
• Object oriented

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The Classical Requirements Phase (contd)

• The classical approach to requirements
• Requirements elicitation
• Requirements analysis
• Construction of a rapid prototype
• Client and future users experiment with the rapid
  prototype

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10.12 Rapid Prototyping

• Hastily built (rapid)
• Imperfections can be ignored
• Exhibits only key functionality
• Emphasis on only what the client sees
• Error checking, file updating can be ignored
• Aim
• To provide the client with an understanding of
  the product

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Rapid Prototyping (contd)

• A rapid prototype is built for change
• Languages for rapid prototyping include 4GLs and
  interpreted languages

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10.13 Human Factors

• The client and intended users must interact with
  the user interface
• Human-computer interface (HCI)
• Menu, not command line
• Point and click
• Windows, icons, pull-down menus

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Human Factors (contd)

• Human factors must be taken into account
• Avoid a lengthy sequence of menus
• Allow the expertise level of an interface to be
  modified
• Uniformity of appearance is important
• Advanced psychology vs. common sense?
• Rapid prototype of the HCI of every product is
  obligatory

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10.14 Reusing the Rapid Prototype

• Reusing a rapid prototype is essentially
  code-and-fix
• Changes are made to a working product
• Expensive
• Maintenance is hard without specification and
  design documents
• Real-time constraints are hard to meet

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Reusing the Rapid Prototype (contd)

• One way to ensure that the rapid prototype is
  discarded
• Implement it in a different language from that of
  the target product
• Generated code can be reused
• We can safely retain (parts of) a rapid prototype
  if
• This is prearranged
• Those parts pass SQA inspections
• However, this is not classical rapid prototyping

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10.15 CASE Tools for the Requirements Workflow

• We need graphical tools for UML diagrams
• To make it easy to change UML diagrams
• The documentation is stored in the tool and
  therefore is always available
• Such tools are sometimes hard to use
• The diagrams may need considerable tweaking
• Overall, the strengths outweigh the weaknesses

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CASE Tools for the Requirements Workflow (contd)

• Graphical CASE environments extended to support
  UML include
• System Architect
• Software through Pictures
• Object-oriented CASE environments include
• Rose
• Together
• ArgoUML (open source)

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10.16 Metrics for the Requirements Workflow

• Volatility and speed of convergence are measures
  of how rapidly the clients needs are determined

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Metrics for the Requirements Workflow (contd)

• The number of changes made during subsequent
  phases
• Changes initiated by the developers
• Too many changes can mean the process is flawed
• Changes initiated by the client
• Moving target problem

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10.17 Challenges of the Requirements Phase

• Employees of the client organization often feel
  threatened by computerization
• The requirements team members must be able to
  negotiate
• The clients needs may have to be scaled down
• Key employees of the client organization may not
  have the time for essential in-depth discussions
• Flexibility and objectivity are essential