1. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 1 Software Engineering September 5, 2001 Introduction to Software Engineering Joseph Conron Computer Science Department New York University jconron@cs.nyu.edu

2. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 2 What is Software Engineering  Software systems are complex  Impossible to understand by a single person  Many projects are never finished: "vaporware"  The problem is arbitrary complexity  1968 Definition:  Software Engineering means the construction of quality software with a limited budget and a given deadline  Our definition:  Software Engineering means the construction of quality software with a limited budget and a given deadline in the context of constant change  Emphasis is on both, on software and on engineering

3. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 3 Software Engineering Concepts: Definitions Project – set of activities to develop a software system Activity – a phase in which related tasks are carried out Task – effort that uses resources AND produces WorkProduct Resources – time, equipment, people (participants) WorkProduct – a model, system, or artifact

4. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 4 Software Engineering Concepts consumes Activity WorkProductResourcesTask Equipment Time ParticipantDocument Model System is produced by * * ** Project

5. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 5 Software Engineering Activities Requirements Elicitation Analysis System Design Object Design Implementation

6. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 6 Introduction to Modeling and UML  What is modeling?  What is UML?  Use case diagrams  Class diagrams  Sequence diagrams  Activity diagrams  Summary

7. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 7 Systems, Models, and Views  A model is an abstraction describing system or a subset of a system  A view depicts selected aspects of a model  A notation is a set of graphical or textual rules for representing views  Views and models of a single system may overlap each other

8. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 8 Systems, Models, and Views Airplane Flightsimulator Scale Model Blueprints Electrical Wiring

9. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 9 Models, Views, and Systems (UML) View * * depicted by described by SystemModel flightSimulator:Model scaleModel:Model blueprints:View airplane:System fuelSystem:ViewelectricalWiring:View

10. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 10 Why model software? Software is already an abstraction: why model software?  Software is getting larger, not smaller  NT 5.0 ~ 40 million lines of code  A single programmer cannot manage this amount of code in its entirety.  Code is often not directly understandable by developers who did not participate in the development  We need simpler representations for complex systems  Modeling is a mean for dealing with complexity

11. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 11 Concepts and Phenomena  Phenomenon: An object in the world of a domain as you perceive it, for example:  The lecture you are attending  My black watch  Concept: Describes the properties of phenomena that are common, for example:  Lectures on software engineering  Black watches  A concept is a 3-tuple:  Its Name distinguishes it from other concepts.  Its Purpose are the properties that determine if a phenomenon is a member of a concept.  Its Members are the phenomena which are part of the concept.

12. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 12  Abstraction: Classification of phenomena into concepts  Modeling: Development of abstractions to answer specific questions about a set of phenomena while ignoring irrelevant details. MembersName Clock Purpose A device that measures time. Concepts and Phenomena

13. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 13 Concepts In Software: Type and Instance  Type:  An abstraction in the context of programming languages  Name: int, Purpose: integral number, Members: 0, -1, 1, 2, -2,...  Instance:  Member of a specific type  The type of a variable represents all possible instances the variable can take.  The relationship between “type” and “instance” is similar to that of “concept” and “phenomenon.”  Abstract data type:  Special type whose implementation is hidden from the rest of the system.

14. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 14 Class  Class:  An abstraction in the context of object-oriented languages  Like an abstract data type, a class encapsulates both state (variables) and behavior (methods)  Unlike abstract data types, classes can be defined in terms of other classes using inheritance Watch time date CalculatorWatch SetDate(d) EnterCalcMode() InputNumber(n) calculatorState

15. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 15 Object-Oriented Modeling UML Package

16. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 16 Application and Solution Domain  Application Domain (Requirements Analysis):  The environment in which the system is operating  Solution Domain (System Design, Object Design):  The available technologies to build the system

17. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 17 What is UML?  UML (Unified Modeling Language)  An emerging standard for modeling object-oriented software.  Resulted from the convergence of notations from three leading object-oriented methods:  OMT (James Rumbaugh)  OOSE (Ivar Jacobson)  Booch (Grady Booch)  Reference: “The Unified Modeling Language User Guide”, Addison Wesley, 1999.  Supported by several CASE tools  Rational ROSE  Together/J ...

18. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 18 UML and This Course  You can model 80% of most problems by using about 20% UML  In this course, we teach you those 20%

19. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 19 UML First Pass  Use case diagrams  Describe the functional behavior of the system as seen by the user.  Class diagrams  Describe the static structure of the system: Objects, Attributes, and Associations.  Sequence diagrams  Describe the dynamic behavior between actors and the system and between objects of the system.  Statechart diagrams  Describe the dynamic behavior of an individual object as a finite state machine.  Activity diagrams  Model the dynamic behavior of a system, in particular the workflow, i.e. a flowchart.

20. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 20 UML First Pass: Use Case Diagrams WatchUserWatchRepairPerson ReadTime SetTime ChangeBattery Actor Use case Package SimpleWatch Use case diagrams represent the functionality of the system from user’s point of view

21. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 21 UML First Pass: Class Diagrams Battery load() 1 2 Time now() PushButton state push() release() 1 1 1 1 1 2 blinkIdx blinkSeconds() blinkMinutes() blinkHours() stopBlinking() referesh() LCDDisplay SimpleWatch Class Association Multiplicity Attributes Operations Class diagrams represent the structure of the system

22. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 22 UML First Pass: Sequence Diagram Object Message Activation Sequence diagrams represent the behavior as interactions blinkHours() blinkMinutes() incrementMinutes() refresh() commitNewTime() stopBlinking() pressButton1() pressButton2() pressButtons1And2() pressButton1() :WatchUser :Time:LCDDisplay:SimpleWatch

23. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 23 button1&2Pressed button1Pressed button2Pressed button1Pressed button1&2Pressed Increment Minutes Increment Hours Blink Hours Blink Seconds Blink Minutes Increment Seconds Stop Blinking UML First Pass: Statechart Diagrams State Initial state Final state Transition Event

24. Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 24 Other UML Notations UML provide other notations that we will be introduced in subsequent lectures, as needed.  Implementation diagrams  Component diagrams  Deployment diagrams  Introduced in lecture on System Design  Object Constraint Language (OCL)  Introduced in lecture on Object Design