1. Using UML, Patterns, and Java Object-Oriented Software Engineering Chapter 1: Introduction

2. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 2 Outline  High quality software: State of the art  Modeling complex systems  Dealing with change:  Software lifecycle  Reuse:  Design Patterns  Frameworks

3. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 3 Can you develop this ?

4. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 4 Requirements Software Limitations of Non-engineered Software Trial and error? Ad-hoc approach? Does it really do what the users need it to do? Can we foresee the requirements?

5. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 5 Software Production has a Poor Track Record Example: Space Shuttle Software  Cost: $10 Billion, millions of dollars more than planned  Time: 3 years late  Quality: First launch of Columbia was cancelled because of a synchronization problem with the Shuttle's 5 onboard computers.  Error was traced back to a change made 2 years earlier when a programmer changed a delay factor in an interrupt handler from 50 to 80 milliseconds.  The likelihood of the error was small enough, that the error caused no harm during thousands of hours of testing.  Substantial errors still exist.  Astronauts are supplied with a book of known software problems "Program Notes and Waivers".

6. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 6 Example: Ariane-5, Flight 501  European Space Agency’s reusable launch vehicle  Cost: 10 years of development and cost of €7 billion€  Launched: 4 June 1996  Mission: $500 million payload to be delivered to orbit  Fate: Veered off course and destructed itself 40 sec. after launch  Conclusions about the cause:  Unhandled floating point exception in Ada Code  Happened due to software specification and design errors  The extensive reviews and tests did not include adequate analysis and testing, which could have detected the potential failure

7. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 7 Other Book Examples of SWE Failures  Denver International Airport  “In 1995, bugs in the automated luggage system... caused suitcases to be chewed up. The airport opened 16 months late, $3.1 billion over budget, with mostly manual luggage system”  Swanick Air Traffic Control System  Controls Air traffic over England and Wales  Delivered in 2002, 6 years late  Substantially over budget ( ￡ 623 M versus the planned ￡ 325 M)

8. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 8 Quality of today’s software….  The average software product released on the market is not error free.  Software bugs, or errors, are so prevalent and so detrimental  They cost the U.S. economy an estimated $59.5 billion annually, or about 0.6% of the gross domestic product, according to a 2002 NIST Report  Software developers spend approximately 80% of development costs on identifying and correcting defects  and yet few products other than software are shipped with such high levels of errors  Complexity of building software solutions

9. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 9 Software Engineering: A Problem Solving Activity  Goal of Software Engineering  Produce high quality software to satisfy a set of functional and nonfunctional requirements  It is a problem solving activity How do we solve a problem?  Analysis: Understand the nature of the problem (requirements) and break the problem into pieces (e.g. Object Identification in OO development)  Synthesis: Put the pieces together into a large structure

10. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 10 Techniques, Methodologies and Tools For problem solving (Analysis and Synthesis) we use  Techniques (methods):  Formal procedures for producing results using some well-defined notation  E.g., algorithms, cook book recipes, etc.  Methodologies:  Collection of techniques applied across software development and unified by a philosophical approach  E.g., a cookbook  Tools:  Instrument or automated systems to accomplish a technique

11. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 11 20 Software Engineering: Definition Software Engineering is a collection of techniques, methodologies and tools that help with the production of  a high quality software system  with a given budget  before a given deadline while change occurs.

12. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 12 Scientist vs Engineer  Computer Scientist  Proves theorems about algorithms, designs languages, defines knowledge representation schemes  Has infinite time…  Engineer  Develops a solution for an application-specific problem for a client  Uses computers & languages, tools, techniques and methods  Software Engineer  Works in multiple application domains  Has only 3 months...  …while changes occurs in requirements and available technology

13. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 13 Comment About SWE Tools: Software/Hardware vs. Grayware vs. Thinkware  Tools can not substitute skill, knowledge and experience  Tool-based analysis is that it is often insufficient or incomplete  System developers are much better at collecting and documenting data than they are at interpreting what these data mean  knowledge and experience, technique skills cannot replace good analysis - people are still needed to think through the problem  The real value is not in the tools and tools output but is in the thought and insight that only the analyst can provide  Being able to use a tool does not mean you understand the underlying techniques, and understanding the techniques does not mean you understand the problem.

14. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 14 Factors affecting the quality of a software system  Complexity:  The system is so complex that no single programmer can understand it anymore  The introduction of one bug fix causes another bug  Change:  The “Entropy” of a software system increases with each change: Each implemented change erodes the structure of the system which makes the next change even more expensive.  As time goes on, the cost to implement a change will be too high, and the system will then be unable to support its intended task. This is true of all systems, independent of their application domain or technological base.

15. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 15 Why are software systems so complex?  The problem domain is difficult  Developers are not experts in the domain  The development process is very difficult to manage  Non-linear development process—dependencies that may not be unless you try the design  Software offers extreme flexibility  No physical constraints on software complexity  No physical constraints on change  Software is a discrete system  Continuous systems have no hidden surprises  Discrete systems have!

16. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 16 Dealing with Complexity 1. Abstraction 2. Decomposition 3. Hierarchy

17. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 17 What is this?

18. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 18 How about this?

19. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 19 1. Abstraction  Inherent human limitation to deal with complexity  The 7 +- 2 phenomena  Chunking: Group collection of objects  Ignore unessential details => Models Remember the following: 10101100110110011000 Remember the following: ACD98

20. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 20 Models are used to provide abstractions  System Model:  Object Model: What is the structure of the system? What are the objects and how are they related?  Functional model: What are the functions of the system? User’s point of view.  Dynamic model: How does the system react to external events? How is the event flow in the system ?  Task Model:  PERT Chart: What are the dependencies between the tasks?  Schedule: How can this be done within the time limit?  Org Chart: What are the roles in the project or organization?  Issues Model:  What are the open and closed issues? What constraints were posed by the client? What resolutions were made? Rationale?

21. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 21 Functional Model Example  Ticket Distribution System WatchUserWatchRepairPerson ReadTime SetTime ChangeBattery SimpleWatch

22. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 22 Object Model Example 1 2 1 1 1 1 1 2 SimpleWatch DisplayBatteryTimePushButton

23. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 23 Dynamic Model Example I (Sequence Diagram) :SimpleWatch:Time:Display pressButton1() blinkHours() blinkMinutes() pressButton2() incrementMinutes() refresh() pressButtons1And2() commitNewTime() stopBlinking() pressButton1() :WatchUser

24. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 24 button1&2Pressed button1Pressed button2Pressed button1Pressed button1&2Pressed Increment Minutes Increment Hours Blink Hours Blink Seconds Blink Minutes Increment Seconds Stop Blinking Dynamic Model Example II (State Diagram)

25. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 25 Task Model Example: Gantt Chart

26. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 26 Task Model Example: PERT Chart

27. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 27 Example of an Issue: Galileo vs the Church  What is the center of the Universe?  Church: The earth is the center of the universe. Why? Aristotle says so.  Galileo: The sun is the center of the universe. Why? Copernicus says so. Also, the Jupiter’s moons rotate round Jupiter, not around Earth.

28. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 28 Issue-Modeling Issue: What is the Center of the Universe? Proposal1: The earth! Proposal2: The sun ! Pro: Copernicus says so. Pro: Aristotle says so. Pro: Change will disturb the people. Con: Jupiter’s moons rotate around Jupiter, not around Earth. Resolution (1615): The church decides proposal 1 is right Resolution (1998): The church declares proposal 1 was wrong

29. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 29 Interdependencies of the Models System Model (Structure, Functionality, Dynamic Behavior) Issue Model (Proposals, Arguments, Resolutions) Task Model (Organization, Activities Schedule)

30. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 30 The “Bermuda Triangle” of Modeling System Models Issue Model Task Models PERT Chart Gantt Chart Org Chart Constraints Issues Proposals Arguments Object Model Functional Model Dynamic Model class... Code Pro Con Forward Engineering Reverse Engineering

31. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 31 Model-based software Engineering: Code is a derivation of object model Problem Statement:A stock exchange lists many companies. Each company is identified by a ticker symbol Analysis phase results in cbject model (UML Class Diagram): StockExchange Company tickerSymbol Lists * * A good software engineer writes as little code as possible public class StockExchange { public Vector m_Company = new Vector(); }; public class Company { public int m_tickerSymbol public Vector m_StockExchange = new Vector(); }; Implementation phase results in code

32. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 32 Which decomposition is the right one? 2. Decomposition  A technique used to master complexity (“divide and conquer”)  Functional decomposition  The system is decomposed into modules  Each module is a major processing step (function) in the application domain  Modules can be decomposed into smaller modules  Object-oriented decomposition  The system is decomposed into classes (“objects”)  Each class is a major abstraction in the application domain  Classes can be decomposed into smaller classes

33. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 33 Functional and OO Decomposition

34. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 34 Functional Decomposition Top Level functions Level 1 functions Level 2 functions Machine Instructions System Function Load R10 Add R1, R10 Read Input Transform Produce Output Set Pointer Read line Open File

35. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 35 Functional Decomposition  Functionality is spread all over the system  Maintainer must understand the whole system to make a single change to the system  Consequence:  Codes are hard to understand  Code that is complex and impossible to maintain  User interface is often awkward and non-intuitive  Example: Microsoft Powerpoint’s Autoshapes

36. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 36 Autoshape Functional Decomposition: Autoshape Draw Rectangle Draw Oval Draw Circle Draw Change Mouse click Change Rectangle Change Oval Change Circle

37. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 37 What is This?

38. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 38 Model of an Eskimo Eskimo Size Dress() Smile() Sleep() Shoe Size Color Type Wear() * Coat Size Color Type Wear()

39. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 39 Iterative Modeling then leads to.... Eskimo Size Dress() Smile() Sleep() Cave Lighting Enter() Leave() lives in but is it the right model? Entrance * Outside Temperature Light Season Hunt() Organize() moves around Windhole Diameter MainEntrance Size

40. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 40 Alternative Model: The Head of an Indian Indian Hair Dress() Smile() Sleep() Mouth NrOfTeeths Size open() speak() * Ear Size listen() Face Nose smile() close_eye()

41. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 41 Class Identification  Class identification is crucial to object-oriented modeling  Basic types of class identification activities: 1.Find the classes for a new software system (from scratch): We call this Greenfield Engineering 2.Identify the classes in an existing system (redesign): We call this Reengineering 3.Create a class-based interface to any system (redesign interface and keep the core): We call this Interface Engineering  What are the limitations? Depending on the purpose of the system different objects might be found  How can we identify the purpose of a system?

42. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 42 What is this Thing?

43. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 43 Modeling a Briefcase BriefCase Capacity: Integer Weight: Integer Open() Close() Carry()

44. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 44 A new Use for a Briefcase BriefCase Capacity: Integer Weight: Integer Open() Close() Carry() SitOnIt()

45. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 45 Questions  Why did we model the thing as “Briefcase”?  Why did we not model it as a chair?  What do we do if the SitOnIt() operation is the most frequently used operation?  The briefcase is only used for sitting on it. It is never opened nor closed.  Is it a “Chair”or a “Briefcase”?  How long shall we live with our modeling mistake?

46. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 46 3. Hierarchy  We got abstractions and decomposition  This leads us to chunks (classes, objects) which we view with object model  Another way to deal with complexity is to provide simple relationships between the chunks  One of the most important relationships is hierarchy  2 important hierarchies  "Part of" hierarchy  "Is-kind-of" hierarchy

47. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 47 Part of Hierarchy Computer I/O Devices CPU Memory Cache ALU Program Counter

48. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 48 Is-Kind-of Hierarchy (Taxonomy) Cell Muscle Cell Blood Cell Nerve Cell Striate Smooth RedWhite Cortical Pyramidal

49. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 49 So where are we right now?  Three ways to deal with complexity:  Abstraction  Decomposition  Hierarchy  Object-oriented decomposition is a good methodology  Unfortunately, depending on the purpose of the system, different objects can be found  How can we do it right?  Many different possibilities  Our current approach: Start with a description of the functionality (Use case model), then proceed to the object model  This leads us to the software lifecycle

50. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 50 Software Lifecycle Activities Subsystems Structured By class... Source Code Implemented By Solution Domain Objects Realized By System Design Object Design Implemen- tation Testing Application Domain Objects Expressed in Terms Of Test Cases ? Verified By class.... ? Requirements Elicitation Use Case Model Analysis...and their models

51. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 51 Software Lifecycle Definition  Software lifecycle:  Set of activities and their relationships to each other to support the development of a software system  Typical Lifecycle questions:  Which activities should I select for the software project?  What are the dependencies between activities?  How should I schedule the activities?

52. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 52 Reusability  A good software design solves a specific problem but is general enough to address future problems (for example, changing requirements)  Experts do not solve every problem from first principles  They reuse solutions that have worked for them in the past  Goal for the software engineer:  Design the software to be reusable across application domains and designs  How?  Use design patterns and frameworks whenever possible

53. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 53 Design Patterns and Frameworks  Design Pattern:  A small set of classes that provide a template solution to a recurring design problem  Reusable design knowledge on a higher level than data structures (link lists, binary trees, etc.)  Framework:  A moderately large set of classes that collaborate to carry out a set of responsibilities in an application domain.  Examples: User Interface Builder  Provide architectural guidance during the design phase  Provide a foundation for software components industry

54. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 54 Patterns are used by many people  Chess Master:  Openings  Middle games  End games  Writer  Tragically Flawed Hero (Macbeth, Hamlet)  Romantic Novel  User Manual  Architect  Office Building  Commercial Building  Private Home  Software Engineer  Composite Pattern: A collection of objects needs to be treated like a single object  Adapter Pattern (Wrapper): Interface to an existing system  Bridge Pattern: Interface to an existing system, but allow it to be extensible

55. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 55 Composite Design Pattern I  Problem: Represent a hierarchy of objects so that leaves and composites are treated uniformly through a common interface  Examples:  Groups of drawable elements. Elements can be grouped into groups. Groups can contain other groups. Elements and groups are operated on (Move, Resize, etc.) uniformly  Hierarchy of files and directories. Directories can contain files and other directories. Same operations are available on files and directories (Move, Copy, Delete, Rename, etc.)  Hierarchy of tasks and subtasks. Tasks (composites) contain smaller subtasks and action items (leaves). Same operations (add, delete, modify, etc.) are applied on tasks, subtasks, and action items.

56. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 56 Composite Design Pattern II  The Component interface specifies the services that are shared among leaf and composite (e.g., move for a drawable element).  A Composite has an aggregation relationship with Component and implements each service by iterating over each contained component.  E.g., Composite.move calls Component.move for each of its contained components  The leave services do the actual work  E.g., Leave.move modifies the coordinates and redraws the leaf Component LeafComposite * Notice the advantages:  Client can use same code to deal with Leaves and Composites  Leaf behavior can independently be changed  New classes of leaf can be added

57. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 57 Summary  Software engineering is a problem solving activity  Developing quality software for a complex problem within a limited time while things are changing  There are many ways to deal with complexity  Modeling, decomposition, abstraction, hierarchy  Issue models: Show the negotiation aspects  System models: Show the technical aspects  Task models: Show the project management aspects  Use Patterns: Reduce complexity even further