Chapter 3 System Models

Transcription

1 March 16, 2009

2 Introduction Graphical models aid in requirements and development

3 Introduction Graphical models aid in requirements and development Different perspectives are possible: external: context or environment modeling behavioral structural: system or data architecture

4 Introduction Graphical models aid in requirements and development Different perspectives are possible: external: context or environment modeling behavioral structural: system or data architecture Leave out details representation, abstraction

5 Introduction Graphical models aid in requirements and development Different perspectives are possible: external: context or environment modeling behavioral structural: system or data architecture Leave out details representation, abstraction types of models: data-flow model architectural model classification model: object model stimulus-response model: state-transition diagrams

6 Introduction Graphical models aid in requirements and development Different perspectives are possible: external: context or environment modeling behavioral structural: system or data architecture Leave out details representation, abstraction types of models: data-flow model architectural model classification model: object model stimulus-response model: state-transition diagrams use UML

7 Outline 1 Context Models 2 Behavioral Models 3 Data Models 4 Object Models

8 Context Models decide early on system boundaries

9 Context Models decide early on system boundaries easy in some cases; flexible in other example: replace existing manual system

10 Context Models decide early on system boundaries easy in some cases; flexible in other example: replace existing manual system next develop context model show context and dependencies on environment detailed relationships are note shown use process or data-flow models

11 Context Model for an ATM System

12 Process Model for Equipment Producrement

13 Outline 1 Context Models 2 Behavioral Models 3 Data Models 4 Object Models

14 Introductiom Describe overall behavior of system Two types: data-flow models state machine models

15 Introductiom Describe overall behavior of system Two types: data-flow models state machine models Businesses rely mostly on data or information use data-flow models for modeling behavior

16 Introductiom Describe overall behavior of system Two types: data-flow models state machine models Businesses rely mostly on data or information use data-flow models for modeling behavior Real-time systems are event driven with minimal data processing use state machines for preseting behavior

17 Data-Flow Models Shows how the system processes data e.g.: filter duplicate records from a customer database

18 Data-Flow Models Shows how the system processes data e.g.: filter duplicate records from a customer database Convention: rounded rectangles: data processing square rectangles: data stores labelled arrows: data flow through system

19 DFD for Order Processing

20 DFD for Insulin Pump

21 Use and Advantages of DFD show a functional perspective each transformation represents a single function or process show end-to-end processing

22 Use and Advantages of DFD show a functional perspective each transformation represents a single function or process show end-to-end processing Simple and intuitive

23 Use and Advantages of DFD show a functional perspective each transformation represents a single function or process show end-to-end processing Simple and intuitive Understandable by system users

24 Use and Advantages of DFD show a functional perspective each transformation represents a single function or process show end-to-end processing Simple and intuitive Understandable by system users Top-down approach, in principle

25 State Machine Models System s responses to internal or external events

26 State Machine Models System s responses to internal or external events Shows system states (one at a time) events that cause transformation between states

27 State Machine Model of a Microwave Oven Figure: UML-based state machine model

28 Microwave Oven States

29 Microwave Oven Stimuli

30 Some Issues with State Machine Models Can grow exponentially with size of system

31 Some Issues with State Machine Models Can grow exponentially with size of system One solution: use super and sub states

32 Microwave Operation Super-state

33 Outline 1 Context Models 2 Behavioral Models 3 Data Models 4 Object Models

34 Data Most software systems focus on data

35 Data Most software systems focus on data independent of system created for the system

36 Data Most software systems focus on data independent of system created for the system Semantic data models: logical form of the data

37 Data Most software systems focus on data independent of system created for the system Semantic data models: logical form of the data

38 Semantic Data Models Most common:

39 Semantic Data Models Most common: entity-relation-attribute model

40 Semantic Data Models Most common: entity-relation-attribute model Usually in third normal form

41 Semantic Data Models Most common: entity-relation-attribute model Usually in third normal form Easy to tranform to OO design

42 Sample ERA mdoel

43 Semantic Data Models Since graphical, lacks details

44 Semantic Data Models Since graphical, lacks details Use data dictionary

45 Semantic Data Models Since graphical, lacks details Use data dictionary keep detailed description of all names

46 Semantic Data Models Since graphical, lacks details Use data dictionary keep detailed description of all names name management

47 Semantic Data Models Since graphical, lacks details Use data dictionary keep detailed description of all names name management organization information storage

48 Data Dictionary

49 Outline 1 Context Models 2 Behavioral Models 3 Data Models 4 Object Models

50 Object-Oriented Modeling Identify classes of objects used in the domain

51 Object-Oriented Modeling Identify classes of objects used in the domain Most commonly modeling technique today

52 Object-Oriented Modeling Identify classes of objects used in the domain Most commonly modeling technique today particularly for interactive systems as compared to what?

53 Object-Oriented Modeling Identify classes of objects used in the domain Most commonly modeling technique today particularly for interactive systems as compared to what? Involves:

54 Object-Oriented Modeling Identify classes of objects used in the domain Most commonly modeling technique today particularly for interactive systems as compared to what? Involves: system requirements in object model

55 Object-Oriented Modeling Identify classes of objects used in the domain Most commonly modeling technique today particularly for interactive systems as compared to what? Involves: system requirements in object model design using objects

56 Object-Oriented Modeling Identify classes of objects used in the domain Most commonly modeling technique today particularly for interactive systems as compared to what? Involves: system requirements in object model design using objects develop in an OO language (Java, C++, Smalltalk,...)

57 Object-Oriented Modeling Identify classes of objects used in the domain Most commonly modeling technique today particularly for interactive systems as compared to what? Involves: system requirements in object model design using objects develop in an OO language (Java, C++, Smalltalk,...) We will learn more in OO design

58 Object-Oriented Modeling Identify classes of objects used in the domain Most commonly modeling technique today particularly for interactive systems as compared to what? Involves: system requirements in object model design using objects develop in an OO language (Java, C++, Smalltalk,...) We will learn more in OO design Represent: data and its processing

59 Object Model Class

60 Object Model Class abstraction over set of objects

61 Object Model Class abstraction over set of objects identifies common attributes and services

62 Object Model Class abstraction over set of objects identifies common attributes and services Object

63 Object Model Class abstraction over set of objects identifies common attributes and services Object executable entity instantiated from a class

64 Object Model Class abstraction over set of objects identifies common attributes and services Object executable entity instantiated from a class models developed during requirements phase focus on: classes relationships not details of objects

65 Object Model Class abstraction over set of objects identifies common attributes and services Object executable entity instantiated from a class models developed during requirements phase focus on: classes relationships not details of objects identification of objects is difficult

66 Unified Modeling Language Developed specifically for OO, circa 1999

67 Unified Modeling Language Developed specifically for OO, circa 1999 Standard graphical language with several notation scheme

68 Unified Modeling Language Developed specifically for OO, circa 1999 Standard graphical language with several notation scheme Class represented as rectangle with sections: name attributes operations

69 UML Example

70 Inheritance Models Class model is organized into a taxonomy

71 Inheritance Models Class model is organized into a taxonomy classification scheme showing how classes are related

72 Inheritance Models Class model is organized into a taxonomy classification scheme showing how classes are related Taxonomy is often shown by inheritance diagram

73 Inheritance Models Class model is organized into a taxonomy classification scheme showing how classes are related Taxonomy is often shown by inheritance diagram general object at top specialized objects at bottom sharing attributes and services

74 Inheritance Models Class model is organized into a taxonomy classification scheme showing how classes are related Taxonomy is often shown by inheritance diagram general object at top specialized objects at bottom sharing attributes and services inheritance show upwards/downwards

75 Inheritance Models Class model is organized into a taxonomy classification scheme showing how classes are related Taxonomy is often shown by inheritance diagram general object at top specialized objects at bottom sharing attributes and services inheritance show upwards/downwards point from subclass to super class

76 Inheritance Models Class model is organized into a taxonomy classification scheme showing how classes are related Taxonomy is often shown by inheritance diagram general object at top specialized objects at bottom sharing attributes and services inheritance show upwards/downwards point from subclass to super class inheritance generalization relationship in UML

77 Library Item Inheritance Model

78 Library User Inheritance Model

79 Object Modeling Requires domain knowledge; subtle issues are common

80 Object Modeling Requires domain knowledge; subtle issues are common For e.g.: why is the title not in Library Item?

81 Object Modeling Requires domain knowledge; subtle issues are common For e.g.: why is the title not in Library Item? how much generalization?

82 Object Modeling Requires domain knowledge; subtle issues are common For e.g.: why is the title not in Library Item? how much generalization?

83 Multiple Inheritance Can inherit from multiple parent classes

84 Multiple Inheritance Can inherit from multiple parent classes

85 Multiple Inheritance Can inherit from multiple parent classes Issues:

86 Multiple Inheritance Can inherit from multiple parent classes Issues: should not inherit unnecessary attributes

87 Multiple Inheritance Can inherit from multiple parent classes Issues: should not inherit unnecessary attributes reorganizing is difficult

88 Multiple Inheritance Can inherit from multiple parent classes Issues: should not inherit unnecessary attributes reorganizing is difficult name clashes

89 Multiple Inheritance Can inherit from multiple parent classes Issues: should not inherit unnecessary attributes reorganizing is difficult name clashes more problematic at programming stage

90 Object Aggregation An object may contain other objects

91 Object Aggregation An object may contain other objects