1. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 1 Chapter 7 Design Engineering Software Engineering: A Practitioner’s Approach, 6/e Chapter 9 Design Engineering

2. 2 What is design? It's where you stand with a food in two worlds—the world of technology and the world of people and human purposes—and you try to bring the two together... —Mitch Kapor, Dr. Dobbs Journal The Roman architecture critic Vitruvius advanced the notion that well-designed buildings were those which exhibited firmness, commodity, and delight. The same might be said of good software. Firmness: A program should not have any bugs that inhibit its function. Commodity: A program should be suitable for the purposes for which it was intended. Delight: The experience of using the program should be a pleasurable one. Here we have the beginnings of a theory of design for software.

3. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 3 Objectives At the end of this chapter, students should be able to: Define what is design Define what is design Explain the important of design Explain the important of design Explain the design process & design quality Explain the design process & design quality Explain the design principles Explain the design principles Understand the fundamental software design concepts Understand the fundamental software design concepts Explain and give examples for each of the design concepts Explain and give examples for each of the design concepts

4. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 4 Analysis Model -> Design Model

5. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 5 Design and Quality the design must implement all of the explicit requirements contained in the analysis model, and it must accommodate all of the implicit requirements desired by the customer. the design must implement all of the explicit requirements contained in the analysis model, and it must accommodate all of the implicit requirements desired by the customer. the design must be a readable, understandable guide for those who generate code and for those who test and subsequently support the software. the design must be a readable, understandable guide for those who generate code and for those who test and subsequently support the software. the design should provide a complete picture of the software, addressing the data, functional, and behavioral domains from an implementation perspective. the design should provide a complete picture of the software, addressing the data, functional, and behavioral domains from an implementation perspective.

6. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 6 Quality Guidelines A design should exhibit an architecture that (1) has been created using recognizable architectural styles or patterns, (2) is composed of components that exhibit good design characteristics and (3) can be implemented in an evolutionary fashion A design should exhibit an architecture that (1) has been created using recognizable architectural styles or patterns, (2) is composed of components that exhibit good design characteristics and (3) can be implemented in an evolutionary fashion  For smaller systems, design can sometimes be developed linearly. A design should be modular; that is, the software should be logically partitioned into elements or subsystems A design should be modular; that is, the software should be logically partitioned into elements or subsystems A design should contain distinct representations of data, architecture, interfaces, and components. A design should contain distinct representations of data, architecture, interfaces, and components. A design should lead to data structures that are appropriate for the classes to be implemented and are drawn from recognizable data patterns. A design should lead to data structures that are appropriate for the classes to be implemented and are drawn from recognizable data patterns.  Data structure is a particular way of storing and organizing data in a computer so that it can be used efficiently.

7. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 7 Quality Guidelines A design should lead to components that exhibit independent functional characteristics. A design should lead to components that exhibit independent functional characteristics. A design should lead to interfaces that reduce the complexity of connections between components and with the external environment. A design should lead to interfaces that reduce the complexity of connections between components and with the external environment. A design should be derived using a repeatable method that is driven by information obtained during software requirements analysis. A design should be derived using a repeatable method that is driven by information obtained during software requirements analysis. A design should be represented using a notation that effectively communicates its meaning. A design should be represented using a notation that effectively communicates its meaning.

8. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 8 Design Principles The design process The design process should not suffer from ‘tunnel vision.’ The design should be traceable to the analysis model. The design should be traceable to the analysis model. The design should not reinvent the wheel. The design should not reinvent the wheel. Reinventing the wheel is a phrase that means to duplicate a basic method that has already previously been created or optimized by others. Reinventing the wheel is a phrase that means to duplicate a basic method that has already previously been created or optimized by others. From Davis [DAV95]

9. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 9 Design Principles The design should “minimize the intellectual distance” between the software and the problem as it exists in the real world. The design should “minimize the intellectual distance” between the software and the problem as it exists in the real world. The design should exhibit uniformity and integration. The design should exhibit uniformity and integration. The design should be structured to accommodate change. The design should be structured to accommodate change. The design should be structured to degrade gently, even when aberrant data, events, or operating conditions are encountered. The design should be structured to degrade gently, even when aberrant data, events, or operating conditions are encountered. Design is not coding, coding is not design. Design is not coding, coding is not design. The design should be assessed for quality as it is being created, not after the fact. The design should be assessed for quality as it is being created, not after the fact. The design should be reviewed to minimize conceptual (semantic) errors. The design should be reviewed to minimize conceptual (semantic) errors. From Davis [DAV95]

10. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 10 Fundamental Concepts abstraction- data, procedure, control abstraction- data, procedure, control - process of hiding unwanted details from the user - process of hiding unwanted details from the user architecture—the overall structure of the software architecture—the overall structure of the software patterns—”conveys the essence” of a proven design solution patterns—”conveys the essence” of a proven design solution modularity—compartmentalization of data and function modularity—compartmentalization of data and function information hiding—controlled interfaces, enabling programmers to restrict access to certain data and code information hiding—controlled interfaces, enabling programmers to restrict access to certain data and code functional independence—single-minded function and low coupling functional independence—single-minded function and low coupling refinement—elaboration of detail for all abstractions refinement—elaboration of detail for all abstractions refactoring—a reorganization technique that simplifies the design refactoring—a reorganization technique that simplifies the design

11. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 11 Data Abstraction door implemented as a data structure manufacturer model number type swing direction inserts lights type type number number weight opening mechanism

12. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 12 Procedural Abstraction open implemented with a "knowledge" of the object that is associated with enter details of enter algorithm

13. Data Abstraction Data abstraction refers to, providing only essential features by hiding its background details. class result { int marks; float percentage; char name[20]; void input(); void output(); } main(){ bank b1; b1.input();b1.output();} These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 13 b1 is an object calling input and output member functions, but that code is invisible to the object b1.

14. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 14Architecture “The overall structure of the software and the ways in which that structure provides conceptual integrity for a system.” [SHA95a] Structural properties. This aspect of the architectural design representation defines the components of a system (e.g., modules, objects, filters) and the manner in which those components are packaged and interact with one another. For example, objects are packaged to encapsulate both data and the processing that manipulates the data and interact via the invocation of methods Extra-functional properties. The architectural design description should address how the design architecture achieves requirements for performance, capacity, reliability, security, adaptability, and other system characteristics. Families of related systems. The architectural design should draw upon repeatable patterns that are commonly encountered in the design of families of similar systems. In essence, the design should have the ability to reuse architectural building blocks.

15. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 15 Patterns Design Pattern Template Pattern name—describes the essence of the pattern in a short but expressive name Intent—describes the pattern and what it does Also-known-as—lists any synonyms for the pattern Motivation—provides an example of the problem Applicability—notes specific design situations in which the pattern is applicable Structure—describes the classes that are required to implement the pattern Participants—describes the responsibilities of the classes that are required to implement the pattern Collaborations—describes how the participants collaborate to carry out their responsibilities Consequences—describes the “design forces” that affect the pattern and the potential trade-offs that must be considered when the pattern is implemented Related patterns—cross-references related design patterns

16. Modularity Modularity – software is divided into separately named and addressable components, sometimes called modules, that are integrated to satisfy problem requirements. Modularity – software is divided into separately named and addressable components, sometimes called modules, that are integrated to satisfy problem requirements. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 16

17. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 17 Modularity: Trade-offs What is the "right" number of modules for a specific software design? optimal number of modules of modules cost of cost of software software number of modules moduleintegrationcost module development cost

18. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 18 Information Hiding module controlled interface "secret" algorithm algorithm data structure data structure details of external interface details of external interface resource allocation policy resource allocation policy clients a specific design decision

19. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 19 Why Information Hiding? reduces the likelihood of “side effects” reduces the likelihood of “side effects” limits the global impact of local design decisions limits the global impact of local design decisions emphasizes communication through controlled interfaces emphasizes communication through controlled interfaces discourages the use of global data discourages the use of global data leads to encapsulation—an attribute of high quality design leads to encapsulation—an attribute of high quality design results in higher quality software results in higher quality software

20. Information Hiding Suppose we have a Time class that counts the time of day: Suppose we have a Time class that counts the time of day: class Time { public: void Display(); private: int ticks; }; These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 20

21. Information Hiding The Display() member function prints the current time onscreen. This member function is accessible to all. It's therefore declared public. The Display() member function prints the current time onscreen. This member function is accessible to all. It's therefore declared public. By contrast, the data member ticks is declared private. Therefore, external users can't access it. By contrast, the data member ticks is declared private. Therefore, external users can't access it. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 21

22. Information Hiding Why we want to do that? Why we want to do that? Likely to change in the future Likely to change in the future If these details were indiscriminately accessible to all, the result would be a maintenance nightmare because every change in an implementation detail would propagate to every piece of code that depends on that detail. If these details were indiscriminately accessible to all, the result would be a maintenance nightmare because every change in an implementation detail would propagate to every piece of code that depends on that detail. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 22

23. Information Hiding For example, if we decide to store the current time as the number of CPU cycles rather than the number of the system's clock ticks, every piece of code that relied on the previous representation would break. For example, if we decide to store the current time as the number of CPU cycles rather than the number of the system's clock ticks, every piece of code that relied on the previous representation would break. By contrast, the public members of a class are its interface. Interfaces are less likely to change. By contrast, the public members of a class are its interface. Interfaces are less likely to change. Regardless of how Display() extracts the current timestamp from ticks, users can be sure that it will "do the right thing" and display the correct time onscreen. Regardless of how Display() extracts the current timestamp from ticks, users can be sure that it will "do the right thing" and display the correct time onscreen. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 23

24. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 24 Stepwise Refinement open walk to door; reach for knob; open door; walk through; close door. repeat until door opens turn knob clockwise; if knob doesn't turn, then take key out; find correct key; insert in lock; endif pull/push door move out of way; end repeat

25. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 25 Functional Independence

26. Cohesion The public interface of a class is cohesive if all of its features are related to the concept that the class represents The public interface of a class is cohesive if all of its features are related to the concept that the class represents This class lacks cohesion: This class lacks cohesion: public class CashRegister { public void enterPayment(int dollars, int quarters, int dimes, int nickels, int pennies)... public static final double NICKEL_VALUE = 0.05; public static final double DIME_VALUE = 0.1; public static final double QUARTER_VALUE = 0.25;... } These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 26

27. Cohesion CashRegister, as described above, involves two concepts: cash register and coin CashRegister, as described above, involves two concepts: cash register and coin Solution: Make two classes: Solution: Make two classes: public class Coin { public Coin(double aValue, String aName){... } public double getValue(){... }... } public class CashRegister { public void enterPayment(int coinCount, Coin coinType) {... }... } These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 27

28. Coupling These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 28

29. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 29 Refactoring Fowler [FOW99] defines refactoring in the following manner: "Refactoring is the process of changing a software system in such a way that it does not alter the external behavior of the code [design] yet improves its internal structure.” When software is refactored, the existing design is examined for redundancy unused design elements inefficient or unnecessary algorithms poorly constructed or inappropriate data structures or any other design failure that can be corrected to yield a better design.

30. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 30 Design Model Elements Data elements Data elements Data model --> data structures Data model --> data structures Data model --> database architecture Data model --> database architecture Architectural elements Architectural elements Application domain Application domain Analysis classes, their relationships, collaborations and behaviors are transformed into design realizations Analysis classes, their relationships, collaborations and behaviors are transformed into design realizations Can be patented Can be patented Interface elements Interface elements the user interface (UI) the user interface (UI) external interfaces to other systems, devices, networks or other producers or consumers of information external interfaces to other systems, devices, networks or other producers or consumers of information internal interfaces between various design components internal interfaces between various design components. Component elements Component elements Deployment elements Deployment elements

31. Design Model Elements Data elements (example: High-level DFD Data elements (example: High-level DFD Source: http://yourdon.com/strucanalysis/wiki/in dex.php?title=Chapter_9 http://yourdon.com/strucanalysis/wiki/in dex.php?title=Chapter_9 http://yourdon.com/strucanalysis/wiki/in dex.php?title=Chapter_9 These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 31

32. Design Model Elements Data elements (example: database diagram Data elements (example: database diagram Source: http://www.svgopen.org/2003/papers/Sv gInterfaceElectricalSwitching/index.html http://www.svgopen.org/2003/papers/Sv gInterfaceElectricalSwitching/index.html http://www.svgopen.org/2003/papers/Sv gInterfaceElectricalSwitching/index.html These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 32

33. Design Model Elements Data elements (example: UML class diagram Data elements (example: UML class diagramSource: http://www.agiledata.org/essays/objectOrientation101.html These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 33

34. Design Model Elements Architectural elements (example: architecture diagram) Architectural elements (example: architecture diagram)Source: http://blog.tmcnet.com/blog/tom-keating/2004/10/index.asp?page=7 34

35. Design Model Elements Architectural elements (example: architecture diagram) Architectural elements (example: architecture diagram) 35

36. Design Model Elements Component elements (example: UML Component Diagram) Component elements (example: UML Component Diagram) Source: http://edn.embarcadero.com/article/31863#component-and-deployment-diagrans http://edn.embarcadero.com/article/31863#component-and-deployment-diagrans These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 36

37. Design Model Elements Deployment elements (example: UML Deployment Diagram) Deployment elements (example: UML Deployment Diagram) Source: http://vinci.org/uml/deploymentx.html http://vinci.org/uml/deploymentx.html These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 37

38. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 38

39. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 39 Design Patterns The best designers in any field have an uncanny ability to see patterns that characterize a problem and corresponding patterns that can be combined to create a solution The best designers in any field have an uncanny ability to see patterns that characterize a problem and corresponding patterns that can be combined to create a solution A description of a design pattern may also consider a set of design forces. A description of a design pattern may also consider a set of design forces. Design forces describe non-functional requirements (e.g., ease of maintainability, portability) associated the software for which the pattern is to be applied. Design forces describe non-functional requirements (e.g., ease of maintainability, portability) associated the software for which the pattern is to be applied. The pattern characteristics (classes, responsibilities, and collaborations) indicate the attributes of the design that may be adjusted to enable the pattern to accommodate a variety of problems. The pattern characteristics (classes, responsibilities, and collaborations) indicate the attributes of the design that may be adjusted to enable the pattern to accommodate a variety of problems.

40. Design Patterns Online pattern searching: http://inventors.about.com/gi/dynamic/offsite.htm?site=http%3A%2F% Fpatents.uspto.gov%2Fpatft%2Findex.html Under Quick Search, try to search pattern no. 7669112. Under Quick Search, try to search pattern no. 7669112. You will get ‘automated spell analysis’ pattern. You will get ‘automated spell analysis’ pattern. 40 These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005

41. 41 Frameworks A framework is not an architectural pattern, but rather a skeleton with a collection of “plug points” (also called hooks and slots) that enable it to be adapted to a specific problem domain. A framework is not an architectural pattern, but rather a skeleton with a collection of “plug points” (also called hooks and slots) that enable it to be adapted to a specific problem domain. Gamma et al note that: Gamma et al note that: Design patterns are more abstract than frameworks. Design patterns are more abstract than frameworks. Design patterns are smaller architectural elements than frameworks Design patterns are smaller architectural elements than frameworks Design patterns are less specialized than frameworks Design patterns are less specialized than frameworks

42. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 42 References Pressman, R. (2003). Software Engineering: A Practitioner's Approach. 6th & 5th edition. New York: McGraw-Hill. Pressman, R. (2003). Software Engineering: A Practitioner's Approach. 6th & 5th edition. New York: McGraw-Hill. Somerville I. (2001). Software Engineering. 6th edition. Addison Wesley Somerville I. (2001). Software Engineering. 6th edition. Addison Wesley http://www.allinterview.com/showanswers/66313.html http://www.allinterview.com/showanswers/66313.html http://www.allinterview.com/showanswers/66313.html http://www.augustana.ab.ca/~mohrj/courses/2006.winter/csc120/slides/ch09/ch09.html http://www.augustana.ab.ca/~mohrj/courses/2006.winter/csc120/slides/ch09/ch09.html http://www.augustana.ab.ca/~mohrj/courses/2006.winter/csc120/slides/ch09/ch09.html http://www.informit.com/guides/content.aspx?g=cplusplus&seqNum=78 http://www.informit.com/guides/content.aspx?g=cplusplus&seqNum=78 http://www.informit.com/guides/content.aspx?g=cplusplus&seqNum=78 ~The End ~