Software Engineering System Modeling Extra examples Dr.Doaa Sami Modified from Sommerville’s originals

2 C. Structural Models

3 1. C l a s s D i a g r a m

attribute values +getlength(): double Class Attributes 7  Visibility name : type [count] = default_value  underline static attributes. Student  Visibility -name: string  +  public - totalStudent:int #  protected + getName(): string  -  private + getTotalStuden()t:int  /  derived  derived attribute: not stored, -length: double -width:double attribute values +getlength(): double +getArea(): double - salary: double + getSalary(): double Rectangle /area:double but can be computed from other +getWidth():double

 Visibility -name: string Class Operations 8  Visibility name (parameters) : return_type  underline static operations. Student  Visibility -name: string  +  public - totalStudent:int  # protected + getName(): string  -  private + getTotalStuden()t:int return_type is omitted if function is: Rectangle  constructor -length: double  void -width:double +getlength(): double +getWidth():double +getArea():double - salary: double + getSalary(): double /area:double

Relationships 9  There are two kinds of Relationships  Association (student enrolls in course).  Generalization (parent-child relationship).  Associations can be further classified as  Aggregation.  Composition.

Association  Associations denote relationships between classes. 10  Associations denote relationships between classes.  Describe the nature of the relationship.  Example:  Student enrolls into course  Course enrolled by a student. Student Course Enrolls

Multiplicity relates to ONE instance of another class. 11  Multiplicity is the number of instances one class relates to ONE instance of another class.  For each association, there are two multiplicity decisions to make, one for each end of the association.  For each instance of Professor, many Sections may be taught.  For each instance of Section, there may be either one or zero Professor as the instructor. Professor Section -name:string 0..1 has 0..* -section#:int +getName():string +getSection#:int

Multiplicity (C++ Implementation) 12 Professor Section -name:string 0..1 has 0..* -section#:int +getName():string +getSection#:int class Professor{ class Section{ // A list of Sections // Proffessor Section sec[4]; Professor prof; string name; int sectionNum; Public: Public: string getName(); int getSectionNum(); }; } ;

Multiplicity Representation 13

Aggregation models a whole-part relationship between an 14 Association is used when both of the involved classes are equaly important.  Aggregation is a special form of association that models a whole-part relationship between an aggregate (the whole) and its parts.  Aggregation shows how classes that are collections are composed of other classes.  Aggregation is a part-of relationship. Car 1 4 Wheel

Composition 15  Composition is a strong form of aggregation.  Aggregation is used to model a whole-part relationship between an aggregate (whole) and its parts.  Composition is a strong form of aggregation.  The whole is the only owner of its part.  Multiplicity on the whole side must be one.  The lifetime of the part is dependent upon the whole.  When Circle is destroyed, Point is also destroyed.  The composite must manage the creation and destruction of its parts.

Composition (C++ Implementation) 16 Restaurant 1 1 Menu class Restaurant{ class Menu{ .... }; Menu m; }; ....

Generalization Cows and Wolfs are Mammals. 17 Rather than learn the detailed characteristics of every entity that we experience, we place these entities in more general classes (animals, cars, houses, etc.) and learn characteristics of these classes.  This allows us to infer that different members of these classes have some common characteristics e.g. Cows and Wolfs are Mammals.

Generalization Cont. 18  In object-oriented languages, generalization is implemented using class inheritance mechanisms.  In a generalization, the attributes and operations associated with higher-level classes (super classes) are also associated with the lower-level classes (sub classes).  Subclasses are inherit the attributes and operations from their Superclasses and then add more specific attributes and operations.

Generalization 19

Association Class association connection to have operations and 20  An association class is a construct that allows an association connection to have operations and attributes.  It used when you need to include another class because it includes valuable information about the relationship.

Example: Information System for School 21