Question

Can a design be cohesive and exhibit a high degree of coupling? Explain your answer and provide an example.

Short answer

No, a design should ideally not be highly cohesive and highly coupled. High cohesion and low coupling are preferred.

Step-by-step solution

Understanding Cohesion and Coupling

Cohesion refers to how closely related the functionalities within a single module are. High cohesion means that the elements within a module are highly related and should stay together. Coupling refers to the degree of interdependence between software modules. High coupling indicates strong interdependencies, while low coupling suggests that changes in one module have little impact on others. Ideally, design aims for high cohesion and low coupling.

Analyzing Design Possibility

The question asks if a design can be both cohesive and exhibit high coupling. Typically, in well-designed systems, modules with high cohesion are intended to have low coupling with other modules. This ensures that the module's internal functionality is coherent but does not overly depend on other modules, allowing them to operate independently. This combination is preferred for maintainability and scalability.

Determining the Viability

While it is possible for a module to have high cohesion (meaning all its internal parts are closely related) and simultaneously have high coupling (meaning it strongly interrelies on other modules), this is generally not considered good design. High coupling can lead to fragile systems where changes in one module propagate to others, creating a maintenance challenge. Such a situation might occur in tightly integrated systems where a module is inherently dependent on services or functions provided by other modules.

Providing an Example

An example of this could be an early-stage prototype system where functionality is rapidly assembled. In such a system, a module responsible for user authentication might have high cohesion because it handles all authentication tasks. However, if it directly interacts with multiple other modules (e.g., user profiles, notifications, account management) to perform authentication, it exhibits high coupling. Thus, any change in these modules might require changes in the authentication module.

Key concepts

Cohesion

Cohesion is a fundamental concept in software design. It describes how well the elements within a single module of a software system work together to accomplish a specific task or function. A module with high cohesion means that its components are highly related to each other. This is desirable because it implies that the module has a clear purpose and focus.

• High Cohesion: Ensures that the module serves a single, focused purpose.
• Low Cohesion: Indicates a module is likely serving multiple functions that may not relate directly to one another.

In software design, striving for high cohesion in modules helps ensure that the system is organized efficiently and functions smoothly. A cohesive module is easier to understand, test, and maintain because all its parts function towards a common goal or task. This leads to improved readability and a reduction in complexity.

Coupling

Coupling defines the level of dependency between different software modules. When we discuss coupling, we typically describe it using the terms "high" and "low."

• High Coupling: Modules are highly dependent on each other, meaning changes in one module often require changes in others. This can lead to brittle systems prone to errors during updates or integrations.
• Low Coupling: Modules operate independently or with minimal dependencies, meaning changes in one module have minimal impact on others.

Aim for low coupling, as it enables you to modify modules and implement changes without affecting others substantially, enhancing the system's flexibility and robustness.

Module Interdependence

The concept of module interdependence is closely related to coupling. It measures how much the functionality of one module depends on other modules within the software system. High module interdependence is not usually desired because:

• It makes the system less flexible as modules cannot be easily reused or adapted without considerable effort.
• It complicates the process of understanding and maintaining the system, due to multiple interconnected parts.

Reducing interdependence increases a system's modularity, allowing individual modules to be reused across different projects or systems, which enhances scalability and maintainability.

Software Maintainability

Software maintainability refers to the ease with which a software system or component can be modified to correct defects, improve performance, or adapt to a changing environment. This is a critical aspect of software design, as software inevitably needs updates or changes over time.

Achieving high software maintainability involves:

• Designing modules with high cohesion and low coupling, making them easier to understand and change.
• Documenting code thoroughly to help understand the system.

Ultimately, focusing on maintainability leads to software systems that are easier to manage, reducing long-term development costs and effort.