Data Modelling (Class Diagram)
A. Key Elements
Class
Attributes
Methods
Relationships
B. Notions and their significance-Class
Used to describe different things in a system
Depicted with the box shape, divided into three sections
Write the name of the thing being depicted to the top
B. Notions and their significance-Attributes
Significant piece of data containing values that describe each instance eg name, id, age
To identify an instance of each class, this is done through Attributes
Also called fields, variables, and properties
Attributes are written in the middle section
Formatted with visibility(-), then lowercase letters, colon (:), data type (string-words, int(integer)-numbers) eg. -userid: string
B. Notions and their significance-Methods
Located at the bottom section of the box
Also called operations or functions
Allow you to specify any behavioral feature of a class
Formatted with visibility(-), then lowercase letters, parentheses (), *(variables and data type) not a must eg +verifyLogin()
C.All other observations that makes the UML
Visibility of attribute or method sets the accessibility for that attribute or method. Minus - sign indicates private, and plus + sign indicates public and can be accessed by any other class. Hash tag# indicates protected and can only be accessed by the same class or its subclasses. Tilde ~ package or default can be used by any other class as long as it's in the same package.
B. Notions and their significance-Relationships
Inheritance
Inherits all the attributes and methods of the superclass (like parent and child)
Attributes added to superclass will be automatically updated to subclasses
A specific attribute can be added to an inheritance and do not affect the superclass or other inheritances
Abstraction is used to instantiate classes with inheritance. The superclass name is put in italics to represent.
Represented with a straight line and an arrow attached pointing towards the parent company
Association
Represented by draw a straight line from one class to another class
A verb is used between the lines to state what happens between the associated classes. There is no dependency between the classes
Aggregation
Special type of association that specifies a whole and its parts
Represented by the straight line with an open diamond shape attached
A relationship where a part can exist outside the relationship
Composition
A relationship where a part can't exist outside the relationship (when a child object cannot exist without the parent)
Represented by the straight line with a closed diamond shape attached
Multiplicity allows you to set numerical constraints on relationships by placing the values in between the straight line from child to parent. They are denoted as follows: 0...1 zero to one (optional), n specific number, 0.. zero to many, 1.. one to many, m...n specific number range