Dr. Tom Hicks. Computer Science Department Trinity University

Transcription

1 Dr. Tom Hicks Computer Science Department Trinity University 1 1

2 About Design With Reuse 2

3 Software Reuse Why Do We Care About Reuse? Historically: In Most Engineering Disciplines, Systems are Designed by Composing Existing Components that have been used in other systems This has always been true in Software Engineering But it is more true since templated OOP components! 3

4 Software Reuse Early Software Engineering was more focused on original development Today s Software Engineering recognizes that to achieve better software, more quickly and at lower cost We need to adopt a design process that is based on systematic reuse Software Engineering Might Reuse Full/Whole Systems Modules/Components Functions/Procedures 4

5 1. Application System Reuse Reuse-Based Software Engineering Offers 3 Reuse Options - 1 The whole of an application system may be reused either by incorporating it without change into other systems (COTS reuse) or by developing application families 5

6 2. Component Reuse Reuse-Based Software Engineering Offers 3 Reuse Options - 2 Components of an application from sub-systems to single objects may be reused 3. Function Reuse Software components that implement a single well-defined function may be reused 6

7 Benefits Of Reuse 7

8 5 Major Benefits Of Reuse Increased Reliability Components exercised in working systems 8

9 5 Major Benefits Of Reuse Reduced Process Risk Less uncertainty in development costs 9

10 5 Major Benefits Of Reuse Effective Use of Components Reuse components instead of people 10

11 5 Major Benefits Of Reuse Standards Compliance Embed standards in reusable components i.e. Reuse Requirements/Specifications 11

12 5 Major Benefits Of Reuse Accelerated Development Avoid original development and hence speed-up production 12

13 Reuse Requirements 13

14 3 Requirements For Design With Reuse - 1 A. It must be possible to find Appropriate Reusable Components 14

15 3 Requirements For Design With Reuse - 2 B. The Reuser of the Component Must be Confident that the Components Will Be Reliable and Will behave as Specified 15

16 3 Requirements For Design With Reuse - 3 C. The Components Bust Be Documented so that they can be understood and, where appropriate, modified 16

17 Search Is On! To Find Appropriate, Documented, Reliable Components! 17

18 Common Reuse Problems 18

19 5 Common Reuse Problems Increased Maintenance Costs 19

20 2. Lack of Tool Support 5 Common Reuse Problems

21 5 Common Reuse Problems Not-Invented-Here Syndrome 21

22 5 Common Reuse Problems Maintaining a Component Library 22

23 5 Common Reuse Problems Finding and Adapting Reusable Components 23

24 Program Generators & Reuse 24

25 Generator-Based Reuse - 1 Program Generators involve the reuse of standard patterns and algorithms These patterns/algorithms are embedded in the generator and parameterized by user commands. A program is then automatically generated! 25

26 Generator-Based Reuse - 2 Generator-Based reuse is possible when domain abstractions and their mapping to executable code can be identified A domain specific language is used to compose and control these abstractions 26

27 3 Types Of Program Generator 3 Types of Program Generators o Application Generators for business data processing o Parser and Lexical Analyzer Generators for language processing o Code Generators in CASE tools Generator-Based Reuse is very cost-effective but its applicability is limited to a relatively small number of application domains It is easier for end-users to develop programs using generators compared to other componentbased approaches to reuse 27

28 Reuse Through Program Generation Application description Program generator Generated program Application domain knowledge Database 28

29 About Components 29

30 About Components - 1 Components provide a service without regard to where the component is executing or its programming language A Component is an Independent Executable Entity that can be made up of one or more executable objects 30

31 About Components - 2 The component interface is published and all interactions are through the published interface Components can range in size from simple functions to entire application systems 31

32 Component Based Development 32

33 CBSE Component-Based Software Engineering (CBSE) is an approach to software development that relies on reuse CBSE has emerged from the failure of objectoriented development to support effective reuse. Single object classes are often too detailed and specific [templated data structure applications tend to be the exception!] 33

34 CBSE Components More Abstract In CBSE, Components are More Abstract than object classes and can be considered to be standalone service providers 34

35 CBSE Processes Component-Based Software Engineering Component-based development can be Integrated into a Standard Software Process by incorporating a Reuse activity in the design process. In Reuse-Driven Development, the System Requirements are Modified to Reflect the Components that are Available 35

36 CBSE Prototyping CBSE usually involves a Prototyping or an incremental development process with components being glued together using a scripting language 36

37 CBSE Problems 37

38 3 Most Common CBSE Problems - 1 Component Incompatibilities may mean that Cost and Schedule Savings are Less Than Expected 38

39 3 Most Common CBSE Problems - 2 Finding & Understanding Components 39

40 3 Most Common CBSE Problems - 3 Managing Evolution as requirements change in situations where it may be impossible to change the system components 40

41 Application Frameworks 41

42 About Application Frameworks Application Frameworks are a sub-system design made up of a collection of abstract and concrete classes and the interfaces between them Application Framework sub-systems are implemented by adding components to fill in parts of the design and by instantiating the abstract classes in the framework Frameworks are moderately large entities that can be reused 42

43 3 Framework Classes System Infrastructure Frameworks Support the development of system infrastructures such as communications, user interfaces and compilers Middleware Integration Frameworks Standards and classes that support component communication and information exchange such as MS SQL Server, MySQL, Oracle, FoxPro, etc. Enterprise Application Frameworks Support the development of specific types of application such as telecommunications or financial systems 43

44 Extending Frameworks Frameworks are Generic and are extended to create a more specific application or sub-system Extending the framework involves 1. Adding concrete classes that inherit operations from abstract classes in the framework 2. Adding methods that are called in response to events that are recognised by the framework Problem with frameworks is their complexity and the time it takes to use them effectively 44

45 COTS 45

46 COTS Product Reuse COTS - Commercial Off-The-Shelf systems COTS Systems are usually Complete Application Systems that offer an API (Application Programming Interface) 46

47 Integrating COTS Building Large Systems by Integrating COTS Systems is now a viable development strategy for some types of system such as database or E-commerce systems 47

48 Problems With COTS Systems 48

49 4 Problems With COTS System Integration - 1 Lack of Control Over Functionality and Performance COTS systems may be less effective than they appear 49

50 4 Problems With COTS System Integration - 1 Problems With COTS System Interface Interaction Different COTS systems may make different assumptions that means interface may be difficult 50

51 4 Problems With COTS System Integration - 3 No Control Over System Evolution COTS vendors, not system users, control evolution 51

52 4 Problems With COTS System Integration - 1 No Control Over Support from COTS vendors COTS vendors may not offer support over the lifetime of the product 52

53 Component Development For Reuse 53

54 Component Development For Reuse #1 Components for reuse may be specially constructed by generalizing existing components 4 Ways To Help Generalize Components & Make Components Reusable 1. Reflect Stable Domain Abstractions 2. Hide State Representation 3. Be as independent as possible 4. Publish exceptions through the component interface 54

55 Component Development For Reuse #2 There is a trade-off between reusability and usability. The more general the interface, the greater the reusability but it is then more complex and hence less usable 55

56 Reusable Components Development Costs The Development Cost of Reusable Components is higher than the cost of specific equivalents. This extra reusability enhancement cost should be an organization rather than a project cost. 56

57 Space & Execution Generic Components may be less space-efficient and may have longer execution times than their specific equivalents 57

58 Reusability Enhancement 58

59 Name Generalization Reusability Enhancement #1 4 Generalizations Names in a Component may be modified so that they are not a direct reflection of a specific application entity ( push/pop on stack) 59

60 Reusability Enhancement #2 4 Generalizations Operation Generalization Operations may be added to provide extra functionality and application specific operations may be removed 60

61 Reusability Enhancement #3 4 Generalizations Exception Generalization Application specific exceptions are removed and exception management added to increase the robustness of the component 61

62 Reusability Enhancement #3 Component Certification 4 Generalizations Component is certified as reusable 62

63 Application Families Also Called Product Lines 63

64 Application Families Product Line An Application Family or Product Line is a related set of applications that has a common, domain-specific architecture It is the common core of the application family that is reused each time a new application is required (maybe AVL Tree) Each specific application is then specialized in some way 64

65 3 Application Family Specializations 1. Platform Specialization Different versions of the application are developed for different platforms 2. Configuration Specialization Different versions of the application are created to handle different peripheral devices 3. Functional Specialization Different versions of the application are created for customers with different requirements 65

66 Inventory Management System Application Families Suppose You Are Developer! 66

67 A Resource Management System User access Program access Add Delete Query Browse Admin Report Resource desc. Screen spec. Report spec. Resource database You might start out with this ultra simplistic description of functionality! 67

68 Resource Database Inventory Management Systems Maintains details of the things that are being managed I/O Descriptions Describes the structures in the resource database and input and output formats that are used Query Level Provides functions implementing queries over the resources Access Interfaces A user interface and an application programming interface 68

69 Application Family Architectures Architectures must be structured in such a way to separate different sub-systems and to allow them to be modified The architecture should also separate entities and their descriptions and the higher levels in the system access entities through descriptions rather than directly 69

70 Library Management System Application Families Suppose You Are Developer! 70

71 A Library System Library user access Add Delete Query Browse Admin Report Issue Return Users Resource desc. Screen spec. Report spec. Library holdings database You might start out with this ultra simplistic description of functionality! 71

72 Library System The resources being managed are the books in the library Additional domain-specific functionality (issue, borrow, etc.) must be added for this application 72

73 Can You See The Potential Component Reuse? Resource Management System User access Program access Add Delete Query Browse Admin Report Resource desc. Screen spec. Report spec. Resource database Library user access Add Delete Query Browse Admin Report Issue Return Users A Library System Resource desc. Screen spec. Report spec. Library holdings database 73

74 Software Engineering CSCI 3342 Dr. Thomas E. Hicks Computer Science Department Trinity University Textbook: Software Engineering By Roger Pressman Textbook: Software Engineering By Ian Sommerville Special Thanks To WCB/McGraw-Hill & Addison Wesley For Providing Graphics Of Some Of Text Book Figures For Use In This Presentation. 74