Question

Using the UML graphical notation for object classes, design the following object classes, identifying attributes and operations. Use your own experience to decide on the attributes and operations that should be associated with these objects. a messaging system on a mobile (cell) phone or tablet a printer for a personal computer a personal music system a bank account a library catalogue

Short answer

Identify classes, define attributes and operations, and represent using UML diagrams.

Step-by-step solution

Determine Object Classes

For each system provided in the exercise, identify the main object class. For instance, for a messaging system, the main object class could be 'Message.' For a printer, it could be 'Printer,' for a music system 'MusicSystem,' for a bank account 'BankAccount,' and for a library catalogue 'Book.'

Identify Attributes for Each Class

List down possible attributes for each class based on their functionality. For example, a 'Message' class may have attributes like 'sender', 'receiver', 'content', 'timestamp'. A 'Printer' might include 'brand', 'model', 'status'. Each object class's attributes should describe its key properties.

Identify Operations for Each Class

Determine the essential operations (methods) that can be performed on each object class. For instance, a 'Message' class might have operations like 'send()', 'receive()', 'delete()'. For a 'BankAccount', you might include 'deposit()', 'withdraw()', 'checkBalance()'. Consider what actions are fundamental to each object's functionality.

Represent Each Class with UML Notation

Draw a class diagram for each object using UML notation. For the 'Message' class, represent it as a rectangle divided into three sections: the class name at the top, attributes in the middle, and operations at the bottom. Do this for each object class identified.

Review and Refine

Check each UML diagram for completeness and clarity. Ensure each attribute and operation accurately reflects the object class's characteristics and interactions. Adjust as necessary to improve the design's accuracy and readability.

Key concepts

Understanding Object Classes

Object classes form the backbone of Object-Oriented Design and are central to the creation of UML diagrams. An object class is essentially a blueprint for objects and encapsulates both the data properties and behaviors. Think of it as a cookie cutter, shaping all cookies identically according to its design. In the context of a software system, object classes help define various entities that interact. For example, in a messaging system, a class could represent a 'Message' or a 'User'. Similarly, in a banking application, 'BankAccount' might be a class that describes accounts. Object classes are fundamental as they enable developers to bundle attributes and operations that define the specific behavior and state of real-world entities.

Attributes and Operations

Attributes and operations are key features of any object class. Attributes are essentially data variables that hold information about the class. They describe the class characteristics, like an ID number, a name, or a timestamp. For instance, in a 'Message' class, attributes could include 'sender', 'receiver', and 'timestamp'. These attributes specify what data the object holds.

On the other hand, operations are functions or methods that can be performed on or by the object. They define the behavior of the class and determine how the class interacts with other classes and users. In 'Message', examples of operations might include 'send()', 'receive()', and 'delete()'. These operations are what the class can "do," providing a way to interact with its attributes and perform tasks.

• Attributes: Define the data structure
• Operations: Define the behavior

Creating Class Diagrams

A class diagram in UML is a visual representation of object classes and their relationships. It is organized with a rectangular shape split into three parts: the top for the class name, the middle for attributes, and the bottom for operations. This clear designation helps in understanding and planning the structure of a system.

Class diagrams are part of UML, which means "Unified Modeling Language," a standardized way to design and diagram software systems. Effective class diagrams help communicate the structure of the system to stakeholders and can reveal insights into the system that might not be immediately obvious through coding alone. They facilitate understanding, especially in large teams or complex projects, by providing a clear guide of what each object class is meant to achieve and how they interact.

Navigating the Design Process

The design process when creating UML diagrams and object classes involves various steps to ensure a comprehensive understanding and execution. It starts with identifying the key object classes relevant to the system. This involves understanding the domain and the specific requirements it entails. Once these are identified, we move to mapping out the detailed aspects of each class with its attributes and operations as discussed earlier.

Following this, each class is represented visually in a diagram to bring clarity to its defined attributes and operations. This aids in verifying the operations and ensuring that they align with the intended use problem and system goals. After completed diagrams, it’s important to review and refine this draft. Think of adjustments as quality tuning to enhance accuracy and readability. This iterative step is vital to morphing initial perceptions into a coherent design blueprint, allowing for a shared understanding and directing subsequent implementation.