Software Design Methodologies: UML in Action

1. Software Design Methodologies: UML in Action Dr. Mohamed Fayad, J.D. Edwards Professor Department of Computer Science & Engineering University of Nebraska, Lincoln Ferguson Hall, P.O. Box 880115 Lincoln, NE 68588-0115 http://www.cse.unl.edu/~fayad ISISTAN Research Institute – Tandil, Argentina

2. Lesson 4: Object Identification - 1 2 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

3. Lesson Objectives • Understand object identification & class classification • Learn how to identify: Objects and classes • Textual Specification Analysis • Data Analysis • Behavior Analysis • Use Case Analysis • Associations and aggregations using Abbott's approach Understand how to use the following approaches: • Data Analysis • Use Case 3 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

4. Classification Involves Ordering Knowledge Finding Similarities • Common Attributes • Common Behaviors OO Classifies Software • Exposes existing commonalities • Invents stable abstractions Goal is a simple & natural design 4 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

5. No Single Best Classification Structure Depends upon • Domain • Application • Experience • Creativity Water Animals ? 5 Air Animals Land Animals ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

6. Same Object Can Be Perceived from Several Perspectives Responsibility-Driven carry things, communicate, maintain its living system Data-Driven head, tail, body, leg 6 Behavior-Driven walk, run, eat ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

7. Textual Specification Analysis Data Analysis Behavior Analysis Use-Case Analysis Responsibility Analysis Object/Class Identification Techniques 7 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

8. Abbott’s Noun Approach Use noun, pronoun, and noun phrases to identify abstract objects and classes. Use singular proper nouns (e.g., sensor number 5) and nouns of direct reference (e.g., the fifth sensor) to identify abstract objects. Use plural and common (e.g., sensor) nouns to identify classes. Use verbs and predicate phrases (e.g., are simultaneously activated) to identify the associated operations. Comments This approach is the oldest approach Textual Analysis Approach 8 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

9. Benefits: Easy for beginners to use Abbott’s mapping should usually work Can be used with pre-existing textual requirements specifications Does not require a complete paradigm shift Risks Indirect Many software engineers are weak in grammar English is vague, Examples Some nouns can be used as verbs and vis versa Some words (e.g., purchase, record) can be used as both nouns and verbs Assumes user’s requirements are coherent, complete and correct No tool support Textual Analysis Approach 10 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

10. Classes should make sense in the problem domain. Good classes classify the objects which need to be modeled in the system. Classes often correspond to NOUNS. Avoid redundant or irrelevant classes which add no value in the problem domain. Remove classes which have no attributes. Selecting Good Classes 12 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

11. After initial pass, discard classes which are: Redundant Irrelevant to the problem domain Vague Attributes If class name has no attributes of its own, it is probably an attribute. Elimination of Inappropriate Classes 11 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

12. The Problem Statement: A simple cash register has a display, an electronic wire with a plug, and a numeric keypad which has keys for subtotal, tax, and total. This cash storage device has a total key which triggers the release on the drawer. The numeric buttons simply place a number on the display screen, the subtotal displays the current total, the tax key computes the tax, and the total key adds the subtotal to the tax. Identify all the classes in this problem statement Use the class elimination rules to eliminate the unnecessary classes. Example 1: Simple Cash Register 12 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

13. We are going to use nouns to find classes Nouns (initial) Register Display Wire Plug Keypad Keys Devices Release Drawer Buttons Screen Number Total Tax Nouns (General Knowledge) 0-9 keys Money Subtotal Key Tax Key Total Key Classes in the initial pass 13 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

14. Eliminating Unnecessary Nouns • Screen ---> Redundant • Number ---> Attribute • Total ---> Attribute • Tax ---> Attribute • 0-9 Key • Value ---> Attribute • Money • Subtotal Key • Tax Key • Total Key • Register • Display • Wire ---> Irrelevant • Plug ---> Irrelevant • Keypad • Keys • Devices ---> Vague • Release ---> Irrelevant • Drawer • Buttons ---> Redundant 14 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

15. Data Analysis Approach 1. Identify abstract objects as table 3. Identify relationships between objects Dog Name Breed Owner Name Happy Poodle Joe Tasha Pit Bull Eric King, Jr. Shepherd Carol Dog Owner Name Address 2. Identify instances as rows in table Carol 2601 Lake St. 15 But how do you find your abstract objects? ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

16. Tangible things -- airplane, book, table Roles -- doctor, professor Incidents -- accident, flight Interactions -- purchase, marriage Specifications -- insurance policy People -- humans who carry out some function Places -- areas set aside for people or things Organizations -- formally organized collections of people, resources. and facilities Analyzing the Domain for Abstract Objects 16 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

17. Associations often refer to verbs of verb phrases Examples: next to, contains, part of, works for, married to, downstream from, connected to, etc. These may be explicit in the problem statement or implicit in the knowledge of the problem domain Write down all candidates, then eliminate unnecessary ones and add others Aggregation is just a common type of association Identifying Associations/Aggregations 17 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

18. Data Flow Diagrams (DFDs) State-Transition Diagrams (STDs) Semantic Nets or Object-Interaction Diagrams (OIDs) Message or communication Diagrams Behavior Analysis 18 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

19. Looking for Behavior • Examine required Processing or behavior of system components • Objectify common behavior • Use inheritance • DFDs may help identify processes Swimmers 19 Flyers Runners ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

20. DFD Approach Use each data store on a DFD to identify an abstract object or class Use (all or part of) the transforms associated with data store to identify associated operations Candidate Objects external entities data stores control transformations Candidate Classes data flows Data Flow Diagrams (DFDs) 20 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

21. Benefits Very well-known approach Many requirements analysis methods are based on DFDs. Tool support exists Does not require paradigm shift Risks Data abstraction Indirect Traditional DFDs have the wrong scope Data Flow Diagrams (DFDs) (cont’d) 21 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

22. State Approach Identify an object or a class for each entity that has a state Benefits Can be used at any time that an object or a class has a finite number of obvious states Risks The state can belong to the entire subsystem or an operation An object or a class may have an infinite number of states. An object or a class may have states that are not all obvious. An object or a class may have only a small number of trivial states. State-Transition Diagrams (STDs) 22 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

23. Use Case Analysis: Baseball System 1 Pitch a Ball Pitcher 1 Hit a Home Run 1 Batter Run the Bases 23 1 Runner on First Base Scored a Run ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

24. Base hit Single base hit In field base hit Outfield base hit Double base hit Triple base hit Home run A home run Two home runs Three home runs Grand Slam Some Use Cases in Baseball Game 24 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

25. A Use Case Description Use Case: Hit a Home Run • When a batter hits a home run, the runners run the bases and reach home plate and score • When a batter hits a home run, the batter runs the bases until reaching the home plate and scores • When the runners score, the score board updates the score board, the game announcer is going crazy and saying “ a big home run ... holy cow ... holy cow “ and the fans are going wild and screaming a lot. • When .. 25 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

26. 1. Define: use case model, use case, specification objects, incident objects, organization objects. 2. List all the object identification techniques 3. What are the benefits and risks of each of these techniques? 4. Describe how do you identify associations and aggregations 5. Explain: a. The same object can be perceived from several perspectives. b. No single best classification structure. c. Classification involves ordering knowledge. d. How to select good classes e. How to eliminate inappropriate classes Discussion Questions 26 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad

27. Check the definition of: Classes, Objects, Attributes, Interfaces, Abstraction, Behavior, Responsibility, Roles, Associations, Aggregation. Describe the following Models: Use Case Model, DFD, STD, OID, OCD. Questions for the Next Lecture 27 ISISTAN Research Institute – Tandil, Argentina -- M.E. Fayad