Information Systems Engineering Class Diagram 1 UML diagrams

Information Systems Engineering Class Diagram 1

UML diagrams *Communication diagram(Collaboration diagram) 2

Class Diagram • A Class diagram is used to display some of the classes and packages in your system • It gives you a static picture of the pieces in the system and of the relationships between them • They help the developers see and plan the structure of the system before the code is written, helping to ensure that the system is well designed from the beginning 3

Class Types: Class Utility • A class utility is a collection of operations • Ex: you may have some mathematical functions—squareroot(), cuberoot(), and so on—that are used throughout your system but don't fit well into any particular class • These functions can be gathered together and encapsulated into a class utility for use by the other classes in the system 4

Class Types: Abstract Class • Abstract Class - is a class that will not be instantiated. In other words, if Class A is abstract, there will never be any objects of Type A in memory. • it exists extensively for inheritance and it must be inherited. There are scenarios in which it is useful to define classes that is not intended to instantiate; because such classes normally are used as base-classes in inheritance hierarchies. (Animal class Example) 5

Class Specifications • Class Name - Unique Name, No spaces, Short, Starting with an uppercase letter • Class Visibility • Public - the class can be seen by all of the other classes in the system • Protected or private - the class can be seen in nested classes • Class Multiplicity - The number of instances that you expect to have of a class • Storage Requirements for a Class - The amount of memory you expect each object of the class to require 6

Class Specifications cont. • Class Persistence • Persistent – the information in objects of the class will be saved to a database or some other form of persistent storage • Transient – the information in objects of the class will not be saved to persistent storage 7

Class Attributes Specifications • Data Type (e. g. string, double, int, etc. . ) • Initial Value – Not required • Visibility • Public - the attribute is visible to all other classes ( + ) • Private - the attribute is not visible to any other class ( - ) • Protected - the class and any of its descendants have access to the attribute (#) 8

Class Attributes Specifications cont. • Containment By Value - the attribute is contained within the class Reference - the attribute is located outside the class, but the class has a pointer to it • Static Attribute - Shared by all instances of the class • Derived Attribute - Created from other attributes , Ex. Area is created from the height and width attributes 9

Class Operations • An operation is a behavior associated with a class • An operation has three parts: • The Operation Name • The Operation Parameters • The Operation Return Type • The parameters are arguments the operation receives as input. The return type is the output of the operation 10

Relationships between classes Class A Superclass Class with parts Subclass Assembly Class name Class B Association (relationship) Inheritance (Generalization) (is-a, kind-of) Aggregation (Part-Of)

Associations A semantic relationship between two or more classes that specifies connections among their instances Example: “An Employee works for a Company”

Aggregation A special form of association that models a whole- part relationship between an aggregate (the whole) and its parts. Models a “is a part-part of” relationship. 4 Car wheels Whole Wheel Part

Generalization Indicates that objects of the specialized class (subclass) are substitutable for objects of the generalized class (super-class) “is kind of” relationship An abstract class Shape Super Class Circle Sub Class Generalization relationship

Generalization A sub-class inherits from its super-class Attributes Operations Relationships A sub-class may Add attributes and operations Add relationships Refine (override) inherited operations

Basic Class Diagram (Example) Head Arm Person Class Student takes

Practice • Draw the classes found in the ATM Withdraw Money use case • Classes • Attributes • Operations 17

ATM Withdraw Money Class Diagram 18