1. CS 5150 1 CS 5150 Software Engineering Lecture 15 Program Design 1

2. CS 5150 2 Administration Test 3 is next Monday The test will cover material from all classes since the beginning of the semester, including next Monday's class.

3. CS 5150 3 Comments on Assignment 2: Schedules The schedule must provide time for: User testing and revisions Program and system testing Revision and correction of problems discovered during testing Deployment Handover and acceptance testing

4. CS 5150 4 Architectural Style - Model/View/Controller Model Controller View Example: Control of a unmanned model aircraft Controller: Receives instrument readings from the aircraft and sends controls signals to the aircraft. Model: Translates data received from and sent to the aircraft, and instructions from the user into a model of flight performance. Uses domain knowledge about the aircraft and flight. View: Displays information about the aircraft to the user and transmits instructions to the model.

5. CS 5150 5 Model/View/Controller: Autonomous Land Vehicle Sensors GPS Sonar Laser Signal processing ModelControl signals Steer Throttle Controls ViewModelController

6. CS 5150 6 Model/View/Controller for Web Applications 1User interacts with the user interface (e.g., presses a mouse button). 2Controller handles input event from the user interface, (e.g., via a registered handler or callback) and converts the event into appropriate user action. 3Controller notifies Model of user action, possibly resulting in a change in Model's state (e.g., update shopping cart.). 4View interacts with Model to generate an appropriate user interface response (e.g., list shopping cart's contents). 5User interface waits for further user interactions. from Wikipedia 10/18/2009

7. CS 5150 7 Model/View/Controller for Web Applications ModelControllerView HTMLHTTP WebBrowser control functions WebBrowser view functions Input events Response

8. CS 5150 8 Program Design in the Modified Waterfall Model Requirements System design Testing Operation & maintenance Program design Implementation (coding) Acceptance & release Feasibility study Requirements Design Implementation

9. CS 5150 9 Program Design The task of program design is to represent the software system functions in a form that can be transformed into one or more executable programs. Given a system architecture, the program design specifies: programs, components, packages, classes and class hierarchies interfaces, protocols (where not part of the system architecture) algorithms, data structures, security mechanisms, operational procedures If the program design is done properly, all design decisions should be made before implementation.

10. CS 5150 10 UML Models UML models (diagrams and specifications) can be used for almost all aspects of program design Diagram gives a general overview of the model, showing the principal elements and how they relate to each other. Specification provides details about each element of the model. Specification for models used in program design should have sufficient detail that they can be used to write code from.

11. CS 5150 11 Class Diagrams Window origin size open() close() move() display() name attributes [local, instance, and class (static) variables] operations [methods] responsibilities [optional text] A class is a description of a set of objects that share the same attributes, operations, relationships, and semantics.

12. CS 5150 12 The "Hello, World!" Applet import java.awt.Graphics; class HelloWorld extends java.applet.Applet { public void paint (Graphics g) { g.drawString ("Hello, World!", 10, 10); } Example from: BJR

13. CS 5150 13 The HelloWorld Example HelloWorld paint() class name operations

14. CS 5150 14 Abstraction for HelloWorld HelloWorld paint() g.drawString ("HelloWorld", 0, 10)" class name operations annotation

15. CS 5150 15 Annotation some text note A note is a symbol for rendering constraints and comments attached to an element or a collection of elements.

16. CS 5150 16 Rational Rose: A Typical Class Diagram

17. CS 5150 17 Specification Fields

18. CS 5150 18 General Specification Fields

19. CS 5150 19 Notation: Relationships A dependency is a semantic relationship between two things in which a change to one may effect the semantics of the other. 0..1 * employer employee An association is a structural relationship that describes a set of links, a link being a connection among objects.

20. CS 5150 20 Relationships ParkingLot ParkingSpace location is_available() 1 1... *

21. CS 5150 21 Notation: Relationships (continued) A generalization is a specialization/generalization relationship is which objects of the specialized element (child) are substitutable for objects of the generalized element (parent). childparent A realization is a semantic relationship between classifiers, wherein one classifier specifies a contract that another classifier guarantees to carry out.

22. CS 5150 22 Generalization Applet HelloWorld paint() Graphics generalization dependency Note that the Applet and Graphics classes are shown elided, i.e., just the name is shown, not the attributes or operations.

23. CS 5150 23 Notation: Interface An interface is a collection of operations that specify a service of a class or component, i.e., the externally visible behavior of that element. ISpelling

24. CS 5150 24 Notation: Package A package is a general-purpose mechanism for organizing elements into groups. Business rules

25. CS 5150 25 Packaging Classes applet awt lang HelloWorld java Graphics package

26. CS 5150 26 Modeling Classes Given a real-life system, how do you decide what classes to use? What terms do the users and implementers use to describe the system? They are candidates for classes. Is each candidate class crisply defined? For each class, what is its set of responsibilities? Are the responsibilities evenly balanced among the classes? What attributes and operations does each class need to carry out its responsibilities?

27. CS 5150 27 Candidate Classes: Application Classes and Solution Classes Application classes represent application concepts. Noun identification is an effective technique to generate candidate application classes. Solution classes represent system concepts, e.g., user interface objects, databases, etc.

28. CS 5150 28 Noun Identification for Application Classes: A Library Example The library contains books and journals. It may have several copies of a given book. Some of the books are reserved for short-term loans only. All others may be borrowed by any library member for three weeks. Members of the library can normally borrow up to six items at a time, but members of staff may borrow up to 12 items at one time. Only members of staff may borrow journals. The system must keep track of when books and journals are borrowed and returned and enforce the rules.

29. CS 5150 29 Noun Identification: A Library Example The library contains books and journals. It may have several copies of a given book. Some of the books are reserved for short-term loans only. All others may be borrowed by any library member for three weeks. Members of the library can normally borrow up to six items at a time, but members of staff may borrow up to 12 items at one time. Only members of staff may borrow journals. The system must keep track of when books and journals are borrowed and returned and enforce the rules.

30. CS 5150 30 Candidate Classes Librarythe name of the system Book Journal Copy ShortTermLoanevent LibraryMember Weekmeasure MemberOfLibraryrepeat Itembook or journal Timeabstract term MemberOfStaff Systemgeneral term Rulegeneral term

31. CS 5150 31 Relations between Classes Bookis anItem Journalis anItem Copyis a copy of a Book LibraryMember Item MemberOfStaffis aLibraryMember Is Item needed?

32. CS 5150 32 Operations LibraryMemberborrowsCopy LibraryMemberreturnsCopy MemberOfStaffborrowsJournal MemberOfStaffreturnsJournal Item not needed yet.

33. CS 5150 33 A Possible Class Diagram MemberOfStaffBookCopyJournal is a copy of 1..* 1 LibraryMember 1 0..* 0..12 1 on loan

34. CS 5150 34 From Candidate Classes to Completed Design Methods used to move to final design: Reuse: Wherever possible use existing components, or class libraries. They may need modification. Restructuring: Change the design to improve, understandability, maintainability, etc. Techniques include merging similar classes, splitting complex classes, etc. Optimization: Ensure that the system meets anticipated performance requirements, e.g., by changed algorithms or restructuring. Completion: Fill all gaps, specify interfaces, etc.

35. CS 5150 35 Coupling and Cohesion Coupling is a measure of the dependencies between two part of a system. If two classes are strongly coupled, it is hard to modify one without modifying the other. Cohesion is a measure of dependencies within part of a system. If a class contains many closely related functions its cohesion is high. Aim for high cohesion within classes and weak coupling between them.

36. CS 5150 36 Rough Sketch: Wholesale System Design is empirical and iterative. The following very artificial example, gives an idea of the process. Example A wholesale merchant supplies retail stores from stocks of goods in a warehouse. What classes would you use to model this business?

37. CS 5150 37 Rough Sketch: Wholesale System RetailStore Warehouse Order Invoice Product Shipment Merchant

38. CS 5150 38 Rough Sketch: Wholesale System Warehouse Order Invoice Product Merchant RetailStore name address contactInfo financialInfo Shipment Responsibilities -track status of shipped products Reversal damaged() return() wrongItem() responsibility (text field)

39. CS 5150 39 Expanding a Class: Modeling Financial Information RetailStore Transaction 1 * association Invoice Payment Which class is responsible for the financial records for a store?

40. CS 5150 40 Modeling Invoice Shipment Invoice invoiceNumber +goodsShipped() -sendInvoice() goodsShipped PartsList adornments + public - private RetailStore ??? invoiceRecord

41. CS 5150 41 Lessons Learned Design is empirical. There is no single correct design. During the design process: Eliding: Elements are hidden to simplify the diagram Incomplete: During the early part of the design process, elements may be missing. Inconsistency: During the early part of the design process, the model may not be consistent The diagram is not the whole design. Diagrams must be backed up with specifications.

42. CS 5150 42 An Exam Question: Object Oriented Design A system generates weather maps using data collected from unattended weather stations. Each weather station collects meteorological data and produces summaries of the data. On request, it sends the summary information to an area computer. The area computer uses a database of digitized maps to generate a set of local weather maps.

43. CS 5150 43 Exam Question: Noun Identification A system generates weather maps using data collected from unattended weather stations. Each weather station collects meteorological data and produces summaries of the data. On request, it sends the summary information to an area computer. The area computer uses a database of digitized maps to generate a set of local weather maps.

44. CS 5150 44 Exam Question: Candidate Classes Systemgeneral term WeatherMap Datasame as MeteorologicalData WeatherStationis this a general term? MeteorologicalDatahow does this relate to WeatherStation? DataSummaryhow does this relate to MeteorologicalData? AreaComputerhardware Databasegeneral term DigitizedMap

45. CS 5150 45 Exam Question: Observations about the Candidate Classes WeatherMapis a DigitizedMap is derived from 1...* DataSummary WeatherStationhas a set of MeteorologicalData MeteorologicalData DataSummaryis derived from MeteorologicalData DigitizedMap Can Meteorological Data be an attribute of WeatherStation? Can DataSummary be combined with WeatherMap?

46. CS 5150 46 Exam Question: Attributes and Operations WeatherStation location metereologicalData collectData() getSummary() WeatherMap location date-time geographicData weather gatherData() printMap() DigitizedMap location geographicData printMap() Or should MetereologicalData be a separate object?

47. CS 5150 47 Exam Question: Class Diagram DigitizedMap 1...* 1 WeatherStation location metereologicalData collectData() getSummary() WeatherMap location date-time geographicData weather gatherData() printMap() summary *