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Case Study: Class Extraction

Case Study: Class Extraction. The Osbert Oglesby Case Study. To get Initial Class Diagram : The aim of entity modeling step is to : extract entity classes, determine their interrelationships, and find their attributes

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Case Study: Class Extraction

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  1. Case Study: Class Extraction

  2. The Osbert Oglesby Case Study • To get Initial Class Diagram : • The aim of entity modeling step is to : • extract entity classes, • determine their interrelationships, • and find their attributes • Simple (yet good) way to begin this step is to use the two-stage noun extraction method

  3. Noun Extraction: Osbert Oglesby Case Study • Stage 1: Describe product in one paragraph: • Reports are to be generated in order to improve the effectiveness of the decision-making process for buying works of art. The reports contain buying and selling information about paintings, which are classified as masterpieces, masterworks, and other paintings

  4. Noun Extraction: Osbert Oglesby • Stage 2: Identify nouns in this paragraph : • Reports are to be generated in order to improve the effectiveness of the decision-making process for buyingworks of art. The reports contain buying and sellinginformation about paintings, which are classified as masterpieces, masterworks, and other paintings

  5. Noun Extraction: Osbert Oglesby • The nouns are : • report, effectiveness, process, buying, work of art, selling, information, painting, masterpiece, masterwork • Next let’s remove some candidates : • effectiveness, process and information are abstract nouns and are therefore unlikely to be entity classes • Nouns buying and selling are derived from the verbs “buy” and “sell”; so probably will be operations of some class

  6. Noun Extraction: Osbert Oglesby (contd) • The nouns are : • Report , effectiveness,process, buying,work of art, selling, information,painting, masterpiece, masterwork • Noun report is more likely to be a boundary class than an entity class • Noun work of art is just a synonym for painting; so remove one of them. • This leaves four candidate entity classes: • Painting Class, Masterpiece Class, Masterwork Class, and Other Painting Class

  7. Second Iteration of Initial Class Diagram • Consider interrelationships between entity classes • A masterpiece is a specific type of painting, and so is a masterwork and an “other painting” : • PaintingClass is therefore the base class • Masterpiece Class, Masterwork Class, and Other Painting Class are subclasses of that base class

  8. Second Iteration of Initial Class Diagram Figure 12.18

  9. Third Iteration of Initial Class Diagram • Class diagram may not reflect aspects of pricing algorithm well ? • When dealing with a masterwork : • “The software product first computes the maximum purchase price as if it were a masterpiece by the same artist” • Conclude : masterwork should have all attributes of a masterpiece (so that its maximum purchase price can be computed as if it were a masterpiece) and, in addition, it may have attributes of its own.

  10. Third Iteration of the Initial Class Diagram (contd) Figure 12.19

  11. Fourth Iteration of Initial Class Diagram • Another aspect of pricing algorithm not reflected in the current class diagram : • “The software product computes the coefficient of similarity between each painting for which there is an auction record and the painting under consideration for purchase” • What if anything should we change ?

  12. Fourth Iteration of Initial Class Diagram • Need Auctioned Painting Class to make these comparisons • Maybe, an auctioned painting must be a subclass of PaintingClass ? • But a painting previously been sold at an auction somewhere else has nothing to do with paintings currently on display for sale in Osbert’s gallery

  13. Fourth Iteration of Initial Class Diagram Figure 12.20

  14. Fourth Iteration of Initial Class Diagram • So now we have that an instance of PaintingClass is either : • A painting that Osbert has bought (an instance of Gallery Painting Class), or • A painting sold at some auction (an instance of Auctioned Painting Class)

  15. Fifth Iteration of Initial Class Diagram • Third aspect of maximum price algorithm not yet modeled is fashionability : • “compute maximum purchase price from formula FA , where F is a constant for that artist (fashionability coefficient) …” • Fashionability or Artist Class is needed : • For a painting of Other Painting Class, we then can then use the artist instance of Fashionability Class to compute maximum price that Osbert should offer to pay

  16. Fifth Iteration of Initial Class Diagram

  17. Initial Class Diagrams ? • Why was the first iteration of class diagram so inadequate? • One-paragraph description correctly did not incorporate the pricing algorithm • But algorithmic details turned out to affect class diagram • Repeated iteration and incrementation will lead to a reasonable class diagram

  18. Initial Class Diagram • Next, let’s add attributes to the class diagram • Later, we’ll be extending classes with operations of that class

  19. Fifth Iteration of Initial Class Diagram • Osbert Application Class will contain operation that starts execution of whole software product Figure 12.22

  20. The Initial Dynamic Model: The Osbert Oglesby Case Study • Dynamic modeling is third step in extracting entity classes • A statechart is constructed that reflects all operations performed by or to the software product • The operations are determined from the scenarios

  21. The Initial Dynamic Model: The Osbert Oglesby Case Study • Initial statechart

  22. The Initial Dynamic Model: The Osbert Oglesby Case Study • In state Osbert Oglesby Event Loop, one of five events can occur: • buy painting selected • sell painting selected • print report selected • update fashionability selected • quit selected

  23. Initial Main Menu: Osbert Oglesby • Graphical user interface (GUI) • “Point and click” Figure 12.25

  24. Dynamic Modeling • In object-oriented paradigm, there is a dynamic model for each class, rather than for the system as a whole : • However, objects in this product never move from one class to another class • Accordingly, a dynamic model for software product as a whole is appropriate

  25. Extracting the Boundary Classes: The Osbert Oglesby Case Study • It is easy to extract boundary classes • Each input screen, output screen, and printed report is generally modeled by a boundary class • One screen should be adequate for all four use cases • Thus one initial boundary class • User Interface Class

  26. Initial Boundary Classes • There are three reports: • The purchases report • The sales report • The future trends report • Content of each report is different • Each report modeled by separate boundary class • So four initial boundary classes :

  27. Extracting Control Classes: Osbert Oglesby Case Study • Extract control classes • Each nontrivial computation modeled by a control class • In case study, there are four computations : • Determine maximum price for Masterpiece • Determine maximum price for Masterwork • Determine maximum price for Painting • Determine if there is a new trend in art purchases • There are therefore four initial control classes

  28. Refining the Use Cases • Refine our use cases based on class extraction as well as analysis of problem thus far

  29. Refining the Use Cases: Osbert Oglesby • Pricing algorithm treats three types of paintings differently • Use case Buy a Painting therefore refined into three separate use cases : • Buy a Masterpiece • Buy a Masterwork • Buy Other Painting

  30. Refining the Use Cases: Osbert Oglesby • Use case Produce a Report also needs to be refined • Purchases and sales report both use simple data extraction • Future trends report involves computation • All three reports use their own boundary classes • Thus Produce a Reportuse case refined into three use cases : • Produce a Purchases Report • Produce a Sales Report • Produce a Future Trends Report

  31. Third Iteration of Use-Case Diagram

  32. Refining the Use Cases: Osbert Oglesby • Implications for remaining UML diagrams : • Buy a Painting use case must be split into three separate descriptions • Produce a Report use case must be split into three separate descriptions

  33. Use Case Buy a Masterpiece

  34. Description of Use Case Buy a Masterpiece

  35. Use-Case Realization • The process of extending and refining use cases is called use-case realization • That is, we aim to flesh them out in more detail and to make them “real”

  36. Use-Case Realization • The realization of a specific scenario of a use case is depicted using some interaction diagram : • either a sequence diagram • or a collaboration diagram

  37. Use-Case Realization • Consider use case • Buy a Masterpiece • Thus far, we have only English description of use cases • Now, let’s make it concrete. • First, consider what classes involved in use case

  38. Buy a Masterpiece Use Case • Class diagram (classes that enter into use case)

  39. Four Classes Germane to the Use Case • User Interface Class • models user interface • Compute Masterpiece Price Class • models computation of price Osbert should offer • Masterpiece Class • The computation involves comparing the masterpiece being considered with masterpieces that have been previously auctioned • Auctioned Painting Class • These masterpieces are all instances of Auctioned Painting Class

  40. Buy a MasterpieceUse Case • Seller does not interact directly with software • Instead, Seller provides data that Osbert enters into the software product • This is indicated in the note (rectangle with top right-hand corner turned over)

  41. Buy a Masterpiece Use Case • Scenario (one possible instance of the use case)

  42. Buy a Masterpiece Use Case • An executing software product uses objects, not classes • Example: • A specific masterpiece is not represented by Masterpiece Class but rather by an object, a specific instance of Masterpiece Class • Such an object is denoted in UML by : Masterpiece Class

  43. Buy a Masterpiece Use Case • A class diagram shows the classes in the use case and their relationships • It does not show the objects • Nor the sequence of messages as they are sent from object to object • Something more is needed .. .

  44. Collaboration Diagram:Buy a Masterpiece • A collaboration diagram (of the realization of the scenario of the use case)

  45. Buy a Masterpiece Use Case • Osbert will not approve the specification document unless he understands it • Accordingly, a written description of the collaboration diagram is needed • The flow of events

  46. Buy a Masterpiece Use Case • Express in words the flow of events of the collaboration diagram (of the realization of scenario of the use case )

  47. 2 Types of Interaction Diagrams • UML supports two different types of interaction diagrams : • Collaboration diagram • Sequence diagram • Both contain the same information (events passed among objects or sequences over time), but displayed in different ways

  48. Buy a Masterpiece Use Case • Sequence diagram equivalent to collaboration diagram

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