Common Mistakes in CRC Modeling (and How to Fix Them)

One of the most common pitfalls in CRC modeling is treating it as a mechanical exercise instead of a thinking tool.

When responsibilities are vague or classes are duplicated, the model fails to reflect real behavior.

My experience working with dozens of teams has shown that the best CRC models emerge not from perfect syntax, but from clear thinking and active collaboration.

This chapter breaks down the most frequent CRC modeling mistakes, explains why they happen, and gives you practical CRC modeling tips to fix them—so your design stays clean, focused, and meaningful.

1. Vague or Overloaded Responsibilities

Vague responsibilities are the most common CRC errors I see in beginner models. Phrases like “handle data” or “manage information” don’t tell you what the class actually does.

These responsibilities are too broad and invite duplication. They also make it hard to assign work meaningfully.

Why it happens

• Designers confuse responsibilities with features or outputs.
• Teams rush to list every possible task without probing deeper.
• Responsibilities are written from the perspective of the system, not the object.

How to fix it: Use action verbs and intent

Replace abstract verbs with specific ones tied to behavior. Turn “handle orders” into “process payment for an order.”

Ask: “What does this class do in response to a request?” The answer should be a single, clear action.

Example: Instead of “maintain user data,” write “validate user email before saving.”

Checklist for strong responsibilities:

• Starts with an action verb (e.g., validate, calculate, notify).
• Describes a single, cohesive task.
• Can be implemented by one method or operation.
• Reflects what the class does, not what it contains.

2. Redundant or Overlapping Classes

When two classes do nearly the same thing, it’s a red flag. It breaks cohesion and increases maintenance cost.

I once saw a banking model with four classes named “Account,” “CheckingAccount,” “SavingsAccount,” and “AccountType.” They all managed balance, interest, and transactions—wasting time and creating inconsistency.

Root causes

• Designers haven’t yet identified the true abstraction.
• Overuse of inheritance without clear hierarchy.
• Trying to predict every possible future variation.

How to fix: Embrace abstraction and role separation

Ask: “What is the core responsibility of this class? Does it really need to be a separate class?”

Group similar behaviors under a single class. If you need to model different types, use roles or state patterns, not redundant classes.

Example: Replace “CheckingAccount” and “SavingsAccount” with a single “Account” class that supports different account types via a type field or polymorphic behavior.

Use this table to compare:

Problem	Fix	CRC Modeling Tip
Multiple classes for minor variations	Use inheritance or type fields	Start with one class. Add variation only when needed.
Classes with identical responsibilities	Combine or refactor into one	Ask: “Can one class do this work better?”
Class names that don’t reflect function	Re-name for intent (e.g., “Service” → “PaymentProcessor”)	Use names that describe behavior, not structure.

3. Weak or Inactive Collaborations

Collaboration is where CRC modeling shines—but only if the links between classes are meaningful.

I’ve seen many models where class A “collaborates with” class B simply because they both appear in the same system. That’s not collaboration—it’s a connection without purpose.

What good collaboration looks like

Collaboration should represent a concrete need: “Class A sends a message to class B to confirm a transaction.”

Weak collaborations often occur when the team hasn’t asked: “Who triggers this behavior?” or “What does this class depend on?”

How to strengthen collaborations

• Only list a collaboration if the class actively sends a message or requests an action.
• Use real method names: “calls calculateInterest()” instead of “interacts with”.
• Revisit collaboration after each responsibility is defined.

Example: Instead of “Order collaborates with Payment,” write “Order requests processPayment() from PaymentService.”

Remember: No message, no collaboration.

4. Neglecting the Role of the Facilitator

CRC is a team activity—yet many groups treat it as an individual task.

Without a facilitator, discussions drift, responsibilities get duplicated, and the model becomes a collection of opinions, not a shared understanding.

Why facilitation matters

• Prevents dominance by one voice.
• Keeps the focus on behavior, not structure.
• Encourages questioning: “Is this really something this class should do?”

Facilitator checklist

• Start with a clear problem statement.
• Encourage “Why?” after each responsibility.
• Pause to discuss conflicts or overlaps.
• Use a timer to keep the session flowing.

Even a simple “no phones” rule increases engagement.

5. Ignoring the “Why” Behind the Design

Some teams build CRC models just to check a box—or because the curriculum says so.

But that’s missing the point. CRC modeling is not a documentation step. It’s a design conversation.

When the team doesn’t know the problem they’re solving, the model becomes a meaningless map.

Ask the right questions

• What user need are we addressing?
• What happens when a customer places an order?
• Who or what is responsible for confirming delivery?

Start with the behavior, not the class. Let the responsibilities guide the class shape.

6. Skipping the Refinement Loop

First-pass CRC models are rarely perfect. That’s normal.

Some teams stop after one round, but good design requires iteration.

I’ve seen models improve dramatically after just one feedback round—when the team re-examined responsibilities and removed redundant collaborations.

Refinement steps

1. Review all responsibilities: are they atomic and action-based?
2. Check collaborations: are messages real and necessary?
3. Look for duplicates: can two classes be combined?
4. Ask: “Can this model answer the original problem?”

Use this as your daily CRC troubleshooting checklist.

Frequently Asked Questions

What’s the biggest CRC modeling mistake in practice?

Writing responsibilities like “manage data” or “do something.” These are too abstract and lead to ambiguous design. Always replace them with specific actions.

How do I know if a class is redundant?

If two classes have identical or nearly identical responsibilities and collaborate with the same partners, they’re likely redundant. Ask: “Can one class cover this work?”

Should I include getters and setters in CRC cards?

No. CRC focuses on behavior, not data access. Getters and setters are implementation details. Save them for the class diagram, not the CRC card.

Can CRC modeling mistakes break my code?

Not directly. But a flawed CRC model often reflects flawed design—leading to poor cohesion, tight coupling, and hard-to-maintain code. The model is a warning sign, not the source.

How do I handle conflicting responsibilities in a team?

Use the facilitator to guide a discussion. Ask: “Who is responsible for this decision?” or “What happens if we delegate this to another class?” Often, the conflict reveals a missing abstraction.

Do I need to use CRC cards in every project?

No. Use them when the problem is complex or the team is new to object-oriented thinking. For simple tasks, CRC might be overkill. But for learning and team alignment, it’s invaluable.