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Introduction to Cohesion
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Today, we'll discuss cohesion, which measures how closely related the functions within a module are. Does anyone know why cohesion is important in software design?
I think it makes the code easier to maintain.
Exactly! High cohesion makes it easier to modify modules without affecting unrelated parts. It contributes to maintainability and better software quality. Remember, cohesion is about the 'singleness of purpose' within a module.
So, what happens if a module has low cohesion?
Good question! Low cohesion can lead to modules performing unrelated tasks, making them harder to understand, maintain, and reuse. It's like trying to juggle different tasks at once without focus.
That makes sense! It's like a messy desk where I can't find anything.
Exactly! Now letβs explore the types of cohesion to understand this concept deeply.
Detailed Classification of Cohesion
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Let's classify the types of cohesion. What do you think is the best type of cohesion?
I believe functional cohesion is the best because everything in the module works towards one goal.
Correct! Functional cohesion is ideal as all elements contribute to a single, well-defined function. Can anyone give me an example of functional cohesion?
Like a function that calculates the square root?
Perfect! What about sequential cohesion?
That's when one process's output becomes the input for the next, right?
Yes! It connects processes logically, like the steps in processing an order. And as we go down the classification, which type do you think is the least desirable?
That would be coincidental cohesion, right, where functions just get grouped randomly?
Exactly! Cohesion classification helps us understand our module's design better. Remember: Functional, Sequential, and Communicational are what we aim for.
Achieving High Cohesion
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Finally, how can we achieve high cohesion in our modules?
Maybe by keeping functions that are related together?
Yes! We should aim to keep modules focused on a single responsibility. What strategies do you think could help us?
We can break down larger modules into smaller ones that are clearly defined.
Exactly! Also, high cohesion is often coupled with low coupling. Why do you think having both is important?
Because it makes the software easier to understand and maintain, reducing dependencies.
Well put! As we conclude, remember to strive for functional, sequential, or communicational cohesion, avoiding the others. High cohesion equals better software development!
Introduction & Overview
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Quick Overview
Standard
The section explores the different types of cohesion in software modules, explaining their definitions, characteristics, and examples. It highlights the relationship between cohesion and software quality attributes like maintainability, reusability, and understandability, concluding with strategies to achieve high cohesion.
Detailed
Lecture 21: Classification of Cohesion - Understanding Module Strength
In software design, cohesion is pivotal as it measures how closely related the functionalities within a module are, indicating the module's single-minded purpose. High cohesion is desirable because it leads to better maintainability, reusability, and understandability of the software modules.
Key Points Covered
21.1 Introduction to Cohesion
- Definition: Cohesion is a qualitative measure of how closely the components of a module relate to one another. High cohesion typically implies that the module has a specific responsibility.
- Importance:
- Maintainability: Easier to modify since changes in one part don't affect unrelated parts.
- Reusability: Clear, focused modules are more likely to be utilized in different contexts.
- Understandability: Simpler modules are easier to grasp and modify.
- Reduced Complexity: Decreased interdependencies lead to a less complex system.
- Goal: Achieve high cohesion, meaning a module fulfills a well-defined task.
21.2 Detailed Classification of Cohesion
Cohesion types range from the most desirable to the least:
1. Functional Cohesion: All parts contribute to a single function (e.g., CalculateSquareRoot()).
2. Sequential Cohesion: Output from one component serves as input to another (e.g., ProcessOrder()).
3. Communicational Cohesion: All actions utilize the same data (e.g., CustomerOperations()).
4. Procedural Cohesion: Activities follow a specific sequence but are unrelated (e.g., startup procedures).
5. Temporal Cohesion: Grouped by time (e.g., StartupTasks()).
6. Logical Cohesion: Various unrelated activities controlled by a parameter (e.g., ProcessFile(fileType)).
7. Coincidental Cohesion: Random grouping of unrelated functions (e.g., MiscellaneousFunctions()).
21.3 Achieving High Cohesion
- Design Principle: Strive for Functional, Sequential, or Communicational Cohesion while avoiding Logical and Coincidental Cohesion.
- Strategies: Break down low cohesion modules into smaller ones to focus on single responsibilities.
- Cohesion and Coupling: High cohesion generally accompanies low coupling, an ideal state in software design.
Audio Book
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Introduction to Cohesion: The Strength Within a Module
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Cohesion is a qualitative measure of the degree to which the elements (e.g., statements, data structures, functions) within a module belong together, or how strongly related or focused the responsibilities of a single module are. It assesses the "singleness of purpose" of a module.
Importance in Software Design:
- Maintainability: Highly cohesive modules are easier to understand, test, and modify because all related functionalities are grouped together. A change in one part of a highly cohesive module is less likely to have unintended side effects in unrelated parts.
- Reusability: Modules with a clear, single purpose are more likely to be reusable in different contexts.
- Understandability: Simpler to grasp the function of a module if it does one thing well.
- Reduced Complexity: Less complexity within the module and fewer interdependencies.
Goal:
High Cohesion (also called Strong Cohesion) is a desirable design principle. It implies that a module performs a well-defined task or handles a single, closely related set of responsibilities.
Detailed Explanation
Cohesion refers to how closely related the tasks inside a software module are. A cohesive module should have a clear purpose and only do one main thing. This makes it easier to maintain because each modular piece is focused; if you need to change one area, you usually wonβt disturb others.
For instance, imagine a toolkit: a toolkit where each tool is intended for a specific job (like a screwdriver or a wrench) is more effective than a toolkit that randomly includes many unrelated tools (like a blender and a hammer).
Examples & Analogies
Think about a restaurant. A highly cohesive restaurant has each staff member with a specific role, like chefs cooking food, waiters serving dishes, and cashiers handling payments. This clear division of labor makes it efficient, just as a software module focused on a single task improves performance and clarity.
Detailed Classification of Cohesion (from Best to Worst)
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- Functional Cohesion (Ideal - Very High Cohesion):
- Definition: All elements of the module contribute to the execution of a single, well-defined function. The module performs exactly one task, and all its parts are essential to that task.
- Characteristics: The module's entire functionality can be described by a single, concise statement.
- Example: A module named CalculateSquareRoot().
- Sequential Cohesion (High Cohesion):
- Definition: The output from one part of the module serves as input to the next part, like a sequence of operations.
- Example: A module ProcessOrder() that validates order data, calculates total cost, and generates an invoice.
- Communicational Cohesion (High Cohesion):
- Definition: All elements of the module operate on the same input data or produce the same output data.
- Example: A module CustomerOperations() that gets customer details, updates customer addresses, and deletes customer records.
- Procedural Cohesion (Medium Cohesion):
- Definition: The elements of the module are grouped together because they follow a specific sequence of execution.
- Example: A module PerformStartup() that initializes the database, loads configuration settings, and authenticates the user.
- Temporal Cohesion (Low Cohesion):
- Definition: The elements of the module are grouped together because they are all executed at the same time.
- Example: A module StartupTasks() that opens a log file, initializes variables, sets the system clock, and displays a welcome message.
- Logical Cohesion (Very Low Cohesion):
- Definition: The elements of the module perform distinct activities but are grouped based on logical similarities.
- Example: A module ProcessFile(fileType) that processes different file types dynamically.
- Coincidental Cohesion (Worst - Very Low Cohesion):
- Definition: Elements are grouped together randomly, with no meaningful relationships.
- Example: A module MiscellaneousFunctions() that includes unrelated functions like printing a report and sorting an array.
Detailed Explanation
Cohesion can be classified from best to worst in several categories. At the top, functional cohesion represents modules that fulfill a single purpose with all its parts contributing directly to that task. Sequential cohesion follows, where parts work in a sequence, and communicational cohesion where parts use shared data. As we move down the list, we see lower forms of cohesion that lead to modules doing multiple unrelated tasks, such as coincidental cohesion, which is essentially a chaotic grouping of functions.
This classification helps developers understand how well-organized their code is, promoting better software design practices.
Examples & Analogies
Imagine a bakery. Functional cohesion would be like a pastry chef who perfectly bakes cakes; every action they take directly relates to baking. Sequential cohesion resembles a kitchen workflow where the prep chef prepares ingredients for the main chef to cook, ensuring each step flows into the next. As we move towards coincidental cohesion, it's like a kitchen where any person can randomly take on any task, leading to chaos and inefficiency.
Achieving High Cohesion
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Design Principle:
Strive for Functional, Sequential, or Communicational Cohesion. Avoid Logical and Coincidental.
Strategies:
- Break down large modules with low cohesion into smaller, more focused modules.
- Each module should have a single, well-defined responsibility.
Relationship with Coupling:
High cohesion often goes hand-in-hand with low coupling.
Detailed Explanation
To achieve high cohesion, developers are encouraged to keep functionalities focused and well-defined. This might involve restructuring complex modules and segmenting them into smaller, manageable parts. By ensuring each module has a single responsibility, they enhance the clarity and maintainability of the code. Notably, modules that exhibit high cohesion also tend to have low coupling, meaning they interact with other modules in a clear and specific manner without being tightly linked to each other.
Examples & Analogies
Consider a library. A highly cohesive library section focuses on a specific genre, like mystery novelsβeach book relates closely to the others, making it easier for readers to find what they want. If the genre were mixed with science fiction or biographies (low cohesion), itβd be harder for patrons to navigate. Similarly, a section that recommends books based on reader's interests (low coupling) provides links to other genres without forcing the reader to sift through unrelated titles.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Cohesion: Refers to the strength of the relationship among the modules of a software system.
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High Cohesion: Indicates a well-defined responsibility for a module, enhancing maintainability and reuse.
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Classification of Cohesion: Ranges from Functional (ideal) to Coincidental (undesirable).
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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A function CalculateSquareRoot() represents functional cohesion as it performs a single task.
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ProcessOrder() showcases sequential cohesion, where the output at each stage serves as input for the next.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
π΅ Rhymes Time
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Cohesion is high when tasks align, keeping functions together makes our code shine.
π Fascinating Stories
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Once there was a software engineer who wrote a module that calculated stats. Every function in it was about statistics. Other modules they wrote turned chaotic with unrelated tasks, leading to troubles later on. The module with aligned functions brought peace and clarity.
π§ Other Memory Gems
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For high cohesion, remember: F, S, C (Functional, Sequential, Communicational).
π― Super Acronyms
FCOY (Functional, Communicational, Optimal Yield) to remember the types of cohesion to strive for.
Flash Cards
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Glossary of Terms
Review the Definitions for terms.
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Term: Cohesion
Definition:
A measure of how closely related and focused the responsibilities of a module are.
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Term: Functional Cohesion
Definition:
The highest level of cohesion where all elements contribute to a single function.
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Term: Sequential Cohesion
Definition:
A type of cohesion where the output from one part serves as input to the next.
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Term: Communicational Cohesion
Definition:
Cohesion where all elements operate on the same input or output data.
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Term: Procedural Cohesion
Definition:
Elements grouped together due to a specific sequence of execution.
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Term: Temporal Cohesion
Definition:
Elements are grouped because they are executed at the same time.
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Term: Logical Cohesion
Definition:
Elements perform logically similar but functionally distinct activities.
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Term: Coincidental Cohesion
Definition:
The lowest level of cohesion where elements are grouped randomly with no meaningful relationship.