Question

How do you identify the classes in a problem domain description?

Short answer

Answer: The key steps to identifying classes within a problem domain description are: 1. Understand the problem domain - Read and understand the problem domain description to identify main concepts, objects, and relationships. 2. Identify objects and properties - Identify individual objects within the domain along with their properties and behaviors. 3. Group objects into classes - Group objects into classes based on common properties, behaviors, object identity, and class hierarchy.

Step-by-step solution

Understand the problem domain

First, read and understand the problem domain description carefully. This will help you identify the main concepts, objects, and relationships that exist within the domain. Try to get a clear understanding of the overall context, purpose, and goals of the problem domain, as this will guide your identification of relevant classes.

Identify objects and properties

With a clear understanding of the problem domain, identify the individual objects that are part of the domain. These objects represent the entities or concepts that are relevant to the problem. For each object, also identify its properties (characteristics or attributes) and behaviors (actions or functions).

Group objects into classes

Based on the objects you've identified, begin to group them into classes. Classes represent a generalized blueprint for a category of objects with similar properties and behaviors. When grouping objects into classes, consider the following criteria: 1. Common properties and behaviors: Objects that share a similar set of properties and behaviors are likely to belong to the same class. 2. Object identity: If two objects have the same set of properties but are considered separate entities based on their identity, they belong to different classes. 3. Class hierarchy: Classes can be organized into a hierarchy where subclasses inherit properties and behaviors from parent classes. This allows for a more organized and efficient representation of classes within the problem domain. By following these guidelines, you will be able to identify the relevant classes within a given problem domain description.

Key concepts

Classes and Objects

In Object-Oriented Programming (OOP), classes and objects form the core building blocks. A "class" can be thought of as a blueprint or template for creating objects, which include both data and behavior. Consider a class like "Car" that defines properties like color, model, and brand, as well as behaviors like drive and stop.
A class does not represent the object itself, but rather a category of objects that share common attributes and functionalities. When an "object" is created from a class, it is termed an "instance" of that class.
For instance, if "Car" is the class, a particular car like a red Toyota Corolla 2018 model is an instance of the "Car" class. The great benefit of using classes lies in their ability to encapsulate data and methods, thereby promoting reuse and modularity in programming. Objects, being specific instances of classes, interact with one another in an OOP application, invoking each other’s behaviors and altering their states through the class-defined methods and properties.

Problem Domain Analysis

To effectively apply Object-Oriented Programming, performing a thorough problem domain analysis is crucial. This process involves:

• Understanding the domain: Begin with reading and comprehending the entire description of the problem domain. This could be a business process, a game, or any system that you are trying to model using OOP.
• Identifying entities and objects: As you analyze the domain, identify key entities—this might be things, places, or concepts that are essential to the problem. For each identified entity, ask yourself what role it plays in the domain and what attributes and behaviors it might have.
• Structuring relationships: Recognizing how these entities relate to each other or interact is vital. These relationships can define how you will structure your classes and objects.

Through domain analysis, you capture the essence of the problem, helping to map it onto an OOP model. The outcome of this analysis aids in determining not only which classes need to be created but also the interactions among these classes.

Class Hierarchy

Class hierarchy is an organizational structure within Object-Oriented Programming that reflects the relationship between different classes. A hierarchy allows you to define a general "parent" class—also known as a superclass—that encapsulates shared attributes and behaviors. "Child" classes, or subclasses, inherit these attributes and behaviors while also introducing their own specific characteristics.
This hierarchical system provides several advantages:

• Reusability: Common functionalities are defined once in the superclass and reused in subclasses, avoiding redundancy.
• Extensibility: New subclasses can be added easily, inheriting existing properties and adding new functionalities without altering the existing codebase significantly.
• Polymorphism: It allows objects to be treated as instances of their parent class, facilitating flexibility and the ability to execute a method in different ways, depending on the object type.

For instance, consider a superclass "Vehicle," which has subclasses like "Car," "Bicycle," and "Truck." Each subclass will inherit the general properties of "Vehicle" like speed and engine type but can also define its own unique properties such as "number of wheels" for bicycles or "cargo capacity" for trucks. This hierarchy helps streamline code and manage complexity in application development.