THE ANALYSIS WORKFLOW I

1. THE ANALYSIS WORKFLOW I

2. The Aims of the Analysis Workflow • To obtain a deeper understanding of the requirements • To describe the requirements in a way that is • Easy to maintain, and • Provides insights into the structure of the target information system

3. Classes • The three class types in the Unified Process are • Entity classes • Boundary classes • Control classes • UML notation

4. Entity Classes • An entity class models information that is long lived • Examples: • Account Class in a banking information system • Painting Class in the Osbert Oglesby information system • Mortgage Class and Investment Class in the MSG Foundation information system • Instances of all these classes remain in the information system for years

5. Boundary Classes • A boundary class models the interaction between the information system and its actors • Boundary classes are generally associated with input and output • Examples: • Purchases Report Class and Sales Report Class in the Osbert Oglesby information system • Mortgage Listing Class and Investment Listing Class in the MSG Foundation information system

6. Control Classes • A control class models complex computations and algorithms • Examples: • Compute Masterpiece Price Class, • Compute Masterwork Price Class, and • Compute Other Painting Price Class in the Osbert Oglesby information system

7. Stereotypes • UML notation for these three types of classes • These are stereotypes (extensions of UML) • UML allows us to define additional constructs that are not part of UML but which we need in order to model a system accurately

8. The Unified Process and Classes • The Unified Process does not describe how classes are extracted • Users of the Unified Process are expected to have a background in object-oriented analysis and design • We temporarily suspend this discussion of the Unified Process to explain how classes are extracted, and then return to the Unified Process

9. Extracting Entity Classes • Entity class extraction consists of three steps that are carried out iteratively and incrementally: • Functional modeling • Present scenarios of all the use cases (a scenario is an instance of a use case) • Class modeling • Determine the entity classes and their attributes • Determine the interrelationships and interactions between the entity classes • Present this information in the form of a class diagram • Dynamic modeling • Determine the operations performed by or to each entity class • Present this information in the form of a statechart

10. Flowchart for Extracting Entity Classes

11. Initial Functional Model: Osbert Oglesby • Recall the Osbert Oglesby use-case diagram:

12. Use Case and Scenario • A use case depicts all possible interactions of a specific kind • A scenario is an instance of a use case • (Just as an object is an instance of a class)

13. Scenario of Use Case Buy a Painting

14. Scenario of Use Case Buy a Painting (contd) • This is a normal scenario • There are six paragraphs in the scenario • Only four of them are numbered • The two unnumbered sentences • “Osbert wishes to buy a masterpiece” and • “Osbert makes an offer below the maximum purchase price—the offer is accepted by the seller” have nothing to do with the interaction between Osbert and the information system • These unnumbered paragraphs are essentially comments

15. Second Scenario of Use Case Buy a Painting • This is an exception scenario • It models an interaction that is not “normal”

16. Third Scenario of Use Case Buy a Painting • This is another exception scenario

17. Normal and Exception Scenarios • Normal and exception scenarios can be combined into an extended scenario

18. Initial Functional Model (contd) • The systems analysis team investigates as many normal and exception scenarios of each use case as time permits • To get the deepest possible understanding of • The domain • The business model, and • The use cases

19. Initial Class Diagram: Osbert Oglesby Case Study • The second step in extracting the entity classes is class modeling • The aim of this step is to extract the entity classes, determine their interrelationships, and find their attributes • Usually, the best way to begin this step is to use the two-stage noun extraction method • Stage 1: Describe the information system in a single paragraph • Stage 2: Identify the nouns in this paragraph, then select the entity classes from those nouns

20. Noun Extraction: Osbert Oglesby Case Study • Stage 1: Describe the information system 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

21. Noun Extraction: Osbert Oglesby (contd) • Stage 2: Identify the 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 • The nouns are report, effectiveness, process, buying, work of art, selling, information, painting, masterpiece, and masterwork

22. Noun Extraction: Osbert Oglesby (contd) • effectiveness, process and information are abstract nouns and are therefore unlikely to be entity classes • Abstract nouns identify things that have no physical existence • Nouns buying and selling are derived from the verbs “buy” and “sell” • They will probably be operations of some class

23. Noun Extraction: Osbert Oglesby (contd) • Noun report is unlikely to be an entity class, because a report is not long lived • A report is much more likely to be a boundary class • Noun work of art is just a synonym for painting

24. First Iteration of the Initial Class Diagram • This leaves four candidate entity classes: • Painting Class, Masterpiece Class, Masterwork Class, and Other Painting Class

25. Second Iteration of the Initial Class Diagram • Consider the interrelationships between the 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

26. Second Iteration of Initial Class Diagram (contd)

27. Third Iteration of the Initial Class Diagram • The class diagram does not reflect aspects of the pricing algorithm • When dealing with a masterwork • “The information system first computes the maximum purchase price as if it were a masterpiece by the same artist”

28. Third Iteration of the Initial Class Diagram (contd) • That is, a masterwork has to have all the 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 • This is modeled in the next slide

29. Third Iteration of the Initial Class Diagram (contd)

30. Fourth Iteration of the Initial Class Diagram • Another aspect of the pricing algorithm that is not reflected in the current class diagram is • “The information system computes the coefficient of similarity between each painting for which there is an auction record and the painting under consideration for purchase”

31. Fourth Iteration of the Initial Class Diagram (contd) • Auctioned Painting Class is needed to make these comparisons • An auctioned painting must be a subclass of PaintingClass • But a painting previously been sold at an auction somewhere in the world has nothing to do with paintings currently on display for sale in Osbert’s gallery

32. Fourth Iteration of the Initial Class Diagram (contd)

33. Fourth Iteration of the Initial Class Diagram (contd) • 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)

34. Fifth Iteration of the Initial Class Diagram • A third aspect of the maximum price algorithm that has not yet been modeled is fashionability • “The information system computes the maximum purchase price from the formula FA , where F is a constant for that artist (fashionability coefficient) …” • Fashionability Class is needed • A painting of Other Painting Class can then use the instance of Fashionability Class for that artist to compute the maximum price that Osbert should offer to pay

35. Fifth Iteration of the Initial Class Diagram (contd)

36. Initial Class Diagram: Osbert Oglesby Case Study • Why was the first iteration of the class diagram so inadequate? • The Osbert Oglesby case study appears to be a straightforward data-processing application • The one-paragraph description correctly did not incorporate the pricing algorithm • Unfortunately, the algorithmic details turned out to be critical to the class diagram

37. Initial Class Diagram: Osbert Oglesby (contd) • The first iteration of the class diagram was no good • However, repeated iteration and incrementation led to a reasonable class diagram • This demonstrates the power of the iterative and incremental approach

38. Initial Class Diagram (contd) • Finally, we add the attributes of each class to the class diagram • For the Osbert Oglesby case study, the result is shown on the next slide • The empty rectangle at the bottom of each box will later be filled with the operations of that class

39. Fifth Iteration of the Initial Class Diagram (contd)

40. Fifth Iteration of the Initial Class Diagram (contd) • Osbert Oglesby Application Class will contain the operation that starts execution of the whole information system

41. Fifth Iteration of the Initial Class Diagram (contd) • The next slide shows the fifth iteration of the initial class diagram, without the attributes, but explicitly reflecting the stereotypes • All eight classes in that figure are entity classes, that is, they model long-lived information • This is also a class diagram • A class diagram depicts classes and their interrelationships; attributes and operations are optional