Sequential Cohesion
Definition and Overview
Sequential cohesion is a term used in software engineering to describe a specific type of cohesion in a software module. Cohesion, in the context of software engineering, refers to the degree to which the responsibilities of a single module are functionally related. In sequential cohesion, the output from one part of the module serves as the input for the next part. This type of cohesion is considered to be stronger than logical cohesion, but weaker than functional cohesion.
Characteristics of Sequential Cohesion
Sequential cohesion is characterized by a module where the elements are linked together in such a way that the output of one element serves as the input for the next. This type of cohesion is often seen in modules that perform a series of related operations, where each operation is dependent on the one that came before it.
The key characteristics of sequential cohesion include:
- Data Flow: The primary characteristic of sequential cohesion is the flow of data from one part of the module to the next. This flow of data is unidirectional, meaning it moves in one direction only.
- Dependence: Each part of the module is dependent on the output of the part that came before it. This means that if one part fails, it can affect the functioning of the subsequent parts.
- Ordering: The parts of the module must be executed in a specific order for the module to function correctly. This is because the output of one part serves as the input for the next.
Advantages of Sequential Cohesion
Sequential cohesion has several advantages in software engineering. These include:
- Efficiency: Sequentially cohesive modules can be more efficient than other types of modules because they can pass data directly from one part of the module to the next without needing to store it in an intermediate location.
- Simplicity: Sequential cohesion can make a module easier to understand because the flow of data through the module is clear and straightforward.
- Modularity: Sequential cohesion supports modularity by allowing a complex task to be broken down into a series of smaller, simpler tasks.
Disadvantages of Sequential Cohesion
Despite its advantages, sequential cohesion also has some potential drawbacks. These include:
- Coupling: Sequentially cohesive modules can be tightly coupled, meaning that changes to one part of the module can have a significant impact on other parts. This can make the module more difficult to modify or maintain.
- Error Propagation: Because each part of the module is dependent on the output of the part that came before it, errors can propagate through the module, potentially leading to incorrect results.
- Testing Difficulty: Sequentially cohesive modules can be more difficult to test than other types of modules because each part of the module is dependent on the output of the part that came before it.
Sequential Cohesion in Practice
In practice, sequential cohesion is often used in software modules that perform a series of related operations. For example, a module that reads data from a file, processes the data, and then writes the processed data back to the file would be an example of a sequentially cohesive module.
Sequential cohesion is also commonly used in pipeline architectures, where data is passed through a series of stages, each of which performs a specific operation on the data.