1. Chapter 1 Software Development

2. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-2 Chapter Objectives Discuss the goals of software development Identify various aspects of software quality Examine several development life cycle models Explore the notation of the Unified Modeling Language (UML) Examine issues related to error handling Introduce the concept of algorithm analysis

3. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-3 Software Development Software Engineering is the study of the techniques and theory that support the development of high-quality software The focus is on controlling the development process to achieve consistently good results We want to: – satisfy the client – the person or organization who sponsors the development – meet the needs of the user – the people using the software for its intended purpose

4. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-4 Goals of Software Engineering Solve the right problem – more difficult than it might seem – client interaction is key Deliver a solution on time and under budget – there are always trade-offs Deliver a high-quality solution – beauty is in the eye of the beholder – we must consider the needs of various stakeholders

5. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-5 FIGURE 1.1 Aspects of software quality

6. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-6 Development Models A development life cycle defines a process to be followed during product development Many software development models have been introduced All of them address the following fundamental issues in one way or another: – problem analysis – design – implementation – evaluation

7. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-7 Problem Analysis We must specify the requirements of the software system Must be based on accurate information Various techniques: – discussions and negotiations with the client – modeling the problem structure and data flow – observation of client activities – analysis of existing solutions and systems

8. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-8 Design We must specify the solution You wouldn't consider building a bridge without a design Design involves determining: – the overall software structure (architecture) – the key objects, classes, and their relationships Alternatives should be considered

9. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-9 Implementation We must turn the design into functional software Too many people consider this the primary act of software development May involve the reuse of existing software components

10. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-10 Evaluation We must verify that the system conforms to the requirements This includes, but goes way beyond, testing code with test cases It is possible to build a system that has no bugs and yet is completely wrong

11. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-11 Maintenance After a system is initially developed, it must be maintained This includes: – fixing errors – making enhancements to meet the changing needs of users The better the development effort, the easier the maintenance tasks will be

12. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-12 The Waterfall Model One of the earliest development models Each stage flows into the next Driven by documentation Advantages: – Lays out clear milestones and deliverables – Has high visibility – managers and clients can see the status Disadvantages: – late evaluation – not realistic in many situations

13. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-13 FIGURE 1.2 The waterfall software development model

14. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-14 The Spiral Model Developed by Barry Boehm in the mid '80s Embraces an iterative process, where activities are performed over and over again for different aspects of the system Designed to reduce the risks involved Continually refines the requirements Each loop through the spiral is a complete phase of the development

15. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-15 FIGURE 1.3 The spiral model of software development

16. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-16 The Evolutionary Model Like the spiral model, an evolutionary approach embraces continual refinement Intermediate versions of the system are created for evaluation by both the developers and the client May be more difficult to maintain depending on the attention given to the iterations

17. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-17 FIGURE 1.4 The evolutionary development model

18. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-18 The Unified Modeling Language The Unified Modeling Language (UML) has become a standard notation for software design It is unified in the sense that it is the synthesis of three separate notations It is language independent It includes various types of diagrams which use specific icons and notations However, it is flexible – the details you include in a given diagram depend on what you are trying to capture and communicate

19. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-19 UML Class Diagrams UML class diagrams include: – The classes used in the system – The static relationships among classes – The attributes and operations of each class – The constraints on the connections among objects An attribute is class level data, including variables and constants An operation is essentially equivalent to a method May include visibility details

20. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-20 FIGURE 1.5 LibraryItem class diagram

21. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-21 FIGURE 1.6 A UML class diagram showing inheritance relationships

22. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-22 FIGURE 1.7 A UML class diagram showing an association

23. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-23 FIGURE 1.8 One class shown as an aggregate of other classes

24. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-24 FIGURE 1.9 A UML diagram showing a class implementing an interface

25. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-25 FIGURE 1.10 One class indicating its use of another

26. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-26 Error Handling How problems are handled in a software system is a key design element In Java, an error generally represents an unrecoverable situation An exception is an unusual situation that might be handled various ways Design questions include: – how are problems identified? – where are exceptions thrown and caught?

27. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-27 Analysis of Algorithms An aspect of software quality is the efficient use of resources, including the CPU Algorithm analysis is a core computing topic It gives us a basis to compare the efficiency of algorithms Example: which sorting algorithm is more efficient?

28. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-28 Growth Functions The analysis is defined in general terms, based on: – the problem size (ex: number of items to sort) – key operation (ex: comparison of two values) A growth function shows the relationship between the size of the problem (n) and the time it takes to solve the problem t(n) = 15n 2 + 45 n

29. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-29 Growth Functions It's not usually necessary to know the exact growth function The key issue is the asymptotic complexity of the function – how it grows as n increases Determined by the dominant term in the growth function This is referred to as the order of the algorithm We often use Big-Oh notation to specify the order, such as O(n 2 )

30. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-30 FIGURE 1.11 Some growth functions and their asymptotic complexity

31. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-31 FIGURE 1.12 Increase in problem size with a ten-fold increase in processor speed

32. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-32 FIGURE 1.13 Comparison of typical growth functions

33. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-33 Analyzing Loop Execution A loop executes a certain number of times (say n) Thus the complexity of a loop is n times the complexity of the body of the loop When loops are nested, the body of the outer loop includes the complexity of the inner loop

34. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-34 Analyzing Loop Execution The following loop is O(n) because the loop executes n times and the body of the loop is O(1): for (int i=0; i<n; i++) { x = x + 1; }

35. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-35 Analyzing Loop Execution The following loop is O(n 2 ) because the loop executes n times and the body of the loop, including a nested loop, is O(n): for (int i=0; i<n; i++) { x = x + 1; for (int j=0; j<n; j++) { y = y - 1; }

36. Copyright © 2005 Pearson Addison-Wesley. All rights reserved. 1-36 SE and Data Structures The data structures examined in this book lay the foundation for developing complex software Software Engineering techniques are needed as our software grows more complex As we discuss data structures, we will also practice good software engineering