How do you evaluate the trade-offs between cohesion and coupling in software modules?

1 What is modularity?

Modularity is the degree to which a software system is composed of independent and interchangeable components, or modules, that can be combined and reused in different ways. Modularity has many benefits for software development, such as reducing complexity, improving readability, facilitating testing, and enabling parallel work. However, modularity also comes with some costs, such as increased overhead, reduced efficiency, and potential conflicts.

2 What is cohesion and coupling?

Cohesion and coupling are two measures of how well a software module is designed. Cohesion refers to how closely related the elements within a module are, while coupling refers to how much a module depends on or interacts with other modules. Ideally, a software module should have high cohesion and low coupling, meaning that it performs a single and well-defined function and has minimal dependencies and interactions with other modules. This makes the module more reliable, understandable, and reusable.

3 How to evaluate cohesion and coupling?

There are different ways to evaluate the cohesion and coupling of software modules, depending on the level of abstraction and the criteria of interest. For example, at the code level, one can use metrics such as lines of code, cyclomatic complexity, or fan-in and fan-out to quantify the cohesion and coupling of a module. At the design level, one can use principles such as the single responsibility principle, the open-closed principle, or the interface segregation principle to guide the cohesion and coupling of a module. At the architectural level, one can use patterns such as the layered architecture, the microservices architecture, or the hexagonal architecture to structure the cohesion and coupling of a module.

4 How to balance cohesion and coupling?

There is no definitive answer to how to balance cohesion and coupling in software modules, as different situations may require different trade-offs. However, some general guidelines can help to achieve a reasonable balance. For example, one can follow the principle of separation of concerns, which states that a module should only deal with one aspect of the problem and delegate other aspects to other modules. One can also follow the principle of information hiding, which states that a module should only expose the necessary details of its implementation and hide the rest from other modules. One can also follow the principle of dependency inversion, which states that a module should depend on abstractions rather than concrete implementations of other modules.

5 How to refactor cohesion and coupling?

Sometimes, a software module may have low cohesion and high coupling, which can lead to issues such as poor quality, low reusability, and high maintenance costs. In such cases, refactoring the module can be beneficial to improve its cohesion and coupling. Refactoring is the process of changing the internal structure of a module without altering its external behavior. Common refactoring techniques to improve cohesion and coupling include extracting methods, classes, and fields; moving methods and fields; introducing parameter objects; and introducing interfaces. Extracting methods and classes can break down a long or complex method into smaller and simpler methods that perform a single task, while moving methods and fields can move them from one class to another class that is more related to its functionality or data. Introducing parameter objects can replace a long list of parameters with a single object that encapsulates them, and introducing interfaces can define the contract of a module and decouple it from its implementation.

6 How to test cohesion and coupling?

Testing is an essential part of software development, as it helps to ensure the correctness, quality, and reliability of a software module. It can also evaluate the cohesion and coupling of a module, as well as identify and fix any issues or defects. Common testing techniques to test cohesion and coupling include unit testing, integration testing, and system testing. Unit testing involves testing a single module in isolation, using mock objects or stubs to simulate the behavior of other modules. Integration testing tests the interaction and communication between multiple modules, using real or simulated data and environments. System testing tests the entire software system as a whole, using real or simulated users and scenarios. All of these techniques can help to verify the functionality and performance of a module, as well as detect any errors or conflicts.