SOFTWARE ENGINEERING

Requirements Modeling

Contents covered in last lecture

• System modeling

• Existing and planned system models

• Unified Modeling Language (UML)

  • UML diagram types

• Context models

  • Example: context model of the MHC-PMS

  • Process perspective

• Activity Diagram

  • Notations

  • Examples

  • Swimlane Diagram

• Interaction models

  • Sequence diagrams

  • Representing Objects

  • Message between Objects

  • Selection and Loop

  • Examples

Contents that will be covered in this lecture

• Structural models

• Class diagrams

  • Classes

  • Relationship

  • Dependency Relationships

  • Generalization Relationships

  • Association Relationships

  • Examples

Structural Models

• Definition: Structural models of software display the organization of a system in terms of the components that make up that system and their relationships.

• Types of Structural Models:

  • Static Models: Show the structure of the system design.

  • Dynamic Models: Show the organization of the system when it is executing.

• Purpose: Creation of structural models occurs during discussion and design of the system architecture.

Class Diagrams

• Definition: Class diagrams are utilized in developing an object-oriented system model that depicts the classes in a system and the relationships (associations) between these classes.

• Object Class: An object class serves as a general definition of one kind of system object.

• Association: A connection between classes indicating a relationship.

• Real-world Representation: During initial stages of software engineering, objects symbolize real-world entities such as a patient, prescription, or doctor.

Classes

• Class Definition: A class describes a set of objects sharing the same attributes, operations, relationships, and semantics.

  • Instances: Each object is an instance of one class; objects cannot belong to multiple classes.

  • Structure and Behavior: All objects of a class share identical structure (attributes) and behavior (methods) but differ in attribute data.

• **Example of Attributes:

  • Person

  • name: String

  • address: Address

  • birthdate: Date

  • ssn: Id

  • methods: eat, sleep, work, play

Relationships in UML

• Definition: Object interconnections (both logical and physical) modeled as relationships.

• Types of Relationships:

  1. Dependency

  2. Generalization

  3. Association

Dependency Relationships

• Example:

  • Class: CourseSchedule

  • Method: add(c: Course)

  • Method: remove(c: Course)

• Explanation: A dependency implies a semantic relationship between two or more elements. For instance, CourseSchedule depends on Course since it's referenced in both methods add and remove.

Generalization Relationships

• Definition: A generalization connects a subclass to its superclass, indicating an inheritance of attributes and behavior from the superclass.

• Specialization: The subclass is a specialized version of the more general superclass.

• Terminology: This relationship is informally referred to as an "Is A" relationship.

• Example:

  • Person

  • Subclasses: Student, TeachingAssistant, Employee

Association Relationships

• Definition: Association denotes a link between two classes that indicates they communicate with each other.

• Multiplicity Example:

  • Notation: Student 1..* Instructor

  • Interpretation: A Student has one or more Instructors.

• Aggregation and Composition: Special associations that model objects containing other objects, indicating a HAS-A relationship:

  • Aggregation: Child can exist independently of the parent.

  • Example: Class (parent) and Student (child); deleting Class does not affect Students.

  • Denoted by a hollow-diamond adornment on the association.

  • Composition: Child cannot exist independently of the parent.

  • Example: House (parent) and Room (child); rooms cannot exist separately from a house.

  • Denoted by a filled-diamond adornment on the association.

Aggregation and Composition Examples

• Aggregation Example:

  • Car has Engine, Transmission; deleting Car does not eliminate Engine and Transmission.

• Composition Example:

  • House has Rooms; removing House results in the removal of Rooms as well.

Example Diagrams

Example: School Diagram

• Entities & Relationships:

  • School offers Department

  • 1..1 Departments

  • 1..* Students attends

  • 1..* Subjects

  • Instructor teaches

Example: Order Processing Class Diagram

• Attributes:

  • Order (date: date)

  • Customer (name: String, address: String, status: String)

  • OrderDetail (quantity: integer, taxStatus: String)

• Operations:

  • +calcSubTotal()

  • +calcTax()

  • +calcWeight()

  • +calcTotal()

Example: Bank Transactions Diagram

• Entities:

  • Customer (attributes: name, address, dob, card number)

  • Bank (attributes: code, address)

  • ATM (attributes: location, managed by)

• Relationships:

  • Account manages ATM Transactions, Current Account, Savings Account

Example: Online Shopping System Diagram

• **Roles and Relationships:

  • Admin manages Products, Customer views and buys products, Payments handled, and Cart functionalities.

• Key Attributes:

  • Payment (CustomerId, Card Type, CardNo)

  • Products (Id, Name, Group, Subgroup)

  • Cart (Id, Number of Products)

• Operations:

  • Admin can View, Add, Delete, Modify Products, manage Shipment and Delivery

  • Customer can buy products, view products, make payment, add or delete from cart.