class diagram

• The topic is Software Modeling [Part 2] for Building Usable Software (2024-2025)

UML Recap

• UML diagram types include behavior and structure diagrams.
• Behavior diagrams include activity, state machine, interaction, and use case diagrams,
• Structure diagrams include class, component, object, composite structure, deployment, package, and profile diagrams

Use Case Diagram

• Visually represents interactions between actors and a system.
• Used to define, understand, and communicate functional requirements of a system.
• Relationships in use case diagrams include <>, <>, and <>.
• <> shows an option that alternates on normal behavior, declaring the extension points in the base use case.
• <> shows uses, complementary functionalities, and logical dependencies, or avoids repetition in two or more separate use cases.
• <> describes a variation on normal behavior or inheritance relations

Activity Diagram

• Models workflows, showing dependencies and coordination between activities within a system.

Library Management System

• Members can register, update information, search for and reserve books
• Books have attributes like title, author, ISBN, and genre.
• The system checks book avilability notifying members about reservations.
• Notifications are sent for successful reservations.

Functional Requirements

• FR1: Library members can register and create accounts.
• FR2: Members should be able to update their contact information.
• FR3: The system stores book details (title, author, ISBN, genre).
• FR4: Members can search for books in the catalog.
• FR5: The system allows members to reserve a book if available.
• FR6: Notifications must be displayed for successful reservations.

Non-Functional Requirements

• NFR1: The system must support at least 100 concurrent users without significant performance degradation.
• NFR2: Search queries should return results within 2 seconds.
• NFR3: The system must support future integration with eBook catalogs.
• NFR4: Member account data must be stored securely using encryption.
• NFR5: The system must provide an intuitive and user-friendly interface.

Use Case: Reserve Book Scenario

• Actor: Library Member
• Precondition: The member must be logged into the system.
• Main Flow:
  • The member searches for a book in the catalog
  • the system checks if the book avilable
    • if available, the member reserves the book; if not the system notifies the member
  • The system confirms the reseration and updates the books avilablilty status
• Postcondition: The book is reserved if it was avialable.

Activity Diagram: Library Book Reservation

• A member logs into the system.
• The member searches the catalog.
• If books avilable, the member reserves the book.
• If the book is not available, the system notifies the member.
• The system confirms the reservation.
• The system updates the book avilablilty.
• The member logs out.

UML 2.X and Class Diagrams

• Class diagrams model the structure of a system by modeling:
  • classes
  • attributes
  • operations or methods
• relationships among objects
• Used in early design phases to identify classes and their relations
• Used during implementation to establish relationships between classes with a high level of detail (attributes, visibility).
• A class is a template for creating objects that share common structure and behavior.
• A class consists of Attributes/Fields which shows the characteristics of the class and Operations/Methods which are the functions of a class.

Attribues and Operations

• Attributes: Represent the structure of a class
• Operations: Represent the class's behavior
• Attributes and Operations can be determined by domain knowledge, looking at the requirements and examining class definitions.
• Operations can be determined by examining interaction between entities

Class Visibility

• Public (+): Visible to all classes
• Private (-): Visible only within the class.
• Protected (#): Visible to subclasses

Class Diagram: Relationships

• Association: Any relationship between classes
• Inheritance: Child class inherits from a parent class
• Aggregation: Two classes are associated but are not as close as in direct association
• Composition: The subobject exists only as long as the contained class exists
• Dependency: X uses Y

Relationships in the Example Library System

• A member is associated with many books (Association).
• The reservation system depends on book availability (Dependency).
• A library contains books, but books can exist independently (Aggregation).
• The system supports different types of members like students, professors, Guests (Generalization).
• A reservation is linked to both a book and member (Association).
• A member recieves notifications (Association).
• A reservation contains a due date so that is reservation is deleted the due date is aslo removed (Composition).

Class Diagrams: Associations

• Shows a bidirectional relationship between two classes.
• Instances of one class is connected to instances of another class.
• Describe the nature of the realtionship by:
• Optional name for an optional reading direction.
• A solid line connecting the classes, optional including an arrow indictating the direction (Navigability).

Class Diagram: Navigability

• A class can define the level of access the Class has to other classes.
• Directional arrows show which classes have access, and is known as Navigability.
• If Class A -> Class B, then Class A has access to Class B
• If Class A <- Class B, then Class B has access to Class A
• If Class A -- Class B, the Classes can access each other's attributes and/or instances

Class Diagram: Multiplicity

• Multiplicity is a notation on class relations.
• It indicates how many ojects can belong to each each type in the elationships.
• 0..1: Zero to One
• n: Specific Number
• 0..*: Zero to Many
• 1..*: One to Many

Class Diagram: Association Example

• A member is associated with multiple books.
• A reservation is linked to both a book and a member
• Members receive notifications

Inheritance (Generalization)

• Represents an "is-a" relationship.
• Child classes inherit the attributes/ operations of the parent class, simplifying the model by eliminating redundancy.
• A solid line is used with a holow arrowhead that points from the child to the parent class.

Aggregation

• Class A is a part of Class B, but Class B can exist independently
• Indicates a "consist of" hierachy
• A component can be part of multiple aggregates
• A component can still be created and destroyed independently of the aggregate.

Composition

• The component can only be part of a single aggregate.
• Exists only together with the aggregate.

Dependency

• Exists between two classes if changes to the definition of one might cause changes to the other.
• Notifications depend on reservations

Class Diagram Modeling: Steps

• There are two main types of Class Diagram Modelling:

  • Data Driven Analysis Data Driven Analysis, Map part of Speech to object Model Components. (i.e. noun/verb analysis.) Nouns usually map to classes, objects, or attributes Verbs usually map to operations or associations.
  • Responsibility Driven Design Responsibility Driven Design, Identify all responsibilities with in the system this should be the high level of responsibilities before deciding on the class’s data-driven analysis

• Step 1: Identify Classes and Attributes by underlining all the nouns in the functional requirements documents and then categorizing them.

• Step 2: identify methods by identifying all the verbs in the use-case digram and adding them to classes

• Step 3: Draw Class Diagram

  • Create a class box for each identified class.
  • Add methods (with parameters and return types) and attributes
  • Include visibility notations (+, -, #).
  • Draw relationships between classes (including multiplicity)
  • Review and redefine

Pyhton Code Example

• Example of classes in python, to show relations, attributes, ect

class Member:
    def __init__(self, member_id, name, contact_info):
        self.MemberID = member_id
        self.Name = name
        self.ContactInfo = contact_info

    def register(self):
        # Implement member registration logic here
        print(f"Member {self.Name) registered successfully.")

    def update_info(self):
        # Implement member information update logic here
        print(f"Member {self.Name}'s information updated.")

class Book:
    def __init_(self, isbn, title, author, genre):
        self.ISBN = isbn
        self.Title = title
        self.Author = author
        self.Genre = genre

    def check_availability(self):
        Implement book availability check logic here
        print(f"Book '{self.Title}' is available.")

    def reserve(self):
        Implement book reservation logic here
        print(f"Book '{self.Title}' reserved successfully.")

## Example usage:
if __name__ == "__main__":
    # Create a Member
    member1 = Member("M12345", "John Doe", "[email protected]")
    member1.register()
    member1.update_info()

    # Create a Book
    book1 = Book("ISBN123", "Sample Book", "Author Name", "Science Fiction")

Class Diagrams

• Class diagrams can show:
  • Division of Responsibility: Providing operations for objects
  • Subclassing: Inheritance and generalization -Navigability / Visibility: Objects knowing about other objects to call thier operations -Aggregation / Composition: Objects are part of other objects -Dependencies: If the design changing of a class will affect others -Interfaces: Used to reduced coupling between objects

Diagrams Help

• It Understands the problem.
• Assists selecting meaningful class names (mapping real-world models into entities).
• It structures of the system (entities and its characteristics).
• Start with a simple diagram and refine it.