3.06_Generalization

Summary

The script explains UML generalization, drawing parallels to object-oriented subclassing. It highlights how a general case (parent use case) shares common behaviors, constraints, and assumptions with multiple specialized cases (child use cases), which each add unique aspects. The concept is illustrated through examples, like an ATM transaction, where different operations like withdrawing or depositing funds are specialized types of a general transaction. The same generalization applies to actors, like a 'customer' and a 'corporate customer.' The script emphasizes testing generalization by asking if the child is a type of the parent.

Takeaways

• 📦 Generalization in UML is similar to subclassing in object-oriented programming, showing a relationship between a general case and specialized cases.
• 🧩 Generalization forms an inheritance hierarchy where a parent use case contains shared behaviors, constraints, and assumptions.
• 🔄 Each child use case shares these common characteristics from the parent but also adds unique elements of its own.
• 🏹 Generalization is represented by a triangular-headed arrow pointing from the child use case back to the parent use case.
• 🔍 Keeping diagrams neat by minimizing the number of arrows is a best practice in drawing UML diagrams.
• 🏦 In the context of an ATM, a general parent use case like 'Do a Transaction' could be specialized into child use cases such as 'Withdraw Cash' or 'Deposit Funds'.
• 💳 All specialized use cases for an ATM share common behaviors like swiping a card and entering a PIN but differ in their unique actions.
• 👥 Generalization can also apply to actors in UML, such as having a 'Corporate Customer' as a specialized actor of a 'Customer'.
• 🔗 To test if a generalization relationship exists, ask if the child is a type of the parent (e.g., 'Is a corporate customer a kind of customer?').
• ❌ Generalization relationships cannot exist between unrelated entities, such as actors and use cases (e.g., 'Is a corporate customer a type of transaction?' doesn't make sense).

Q & A

What is generalization in UML?

Generalization in UML is similar to the object-oriented concept of subclassing. It shows a relationship between a general case (parent) and one or more specialized cases (children), creating a kind of inheritance hierarchy.

What does the parent use case represent in UML generalization?

The parent use case contains a set of behaviors, constraints, and assumptions that are shared by all child use cases, which are specialized versions of the parent.

Why is it important to have more than one child use case in UML generalization?

Having more than one child use case makes the generalization meaningful, as each child shares common behaviors with the parent but adds something unique, justifying the need for separate use cases.

How is the generalization relationship represented in UML diagrams?

The generalization relationship is represented by a triangular-headed arrow that points from the child use case back to the parent use case.

What is a good practice for keeping UML diagrams neat when showing generalization relationships?

A good practice is to minimize the number of arrows in your UML diagram, which can be done by grouping multiple child use cases under a single parent with one generalized relationship.

Can you provide an example of generalization in an ATM system?

In an ATM system, a parent use case could be 'Do a transaction,' and child use cases could be 'Withdraw cash,' 'Deposit funds,' and 'Transfer funds.' Each child shares common behaviors, like swiping a card and entering a PIN, but adds unique actions related to the specific transaction.

Can generalization relationships exist between actors in UML?

Yes, generalization relationships can exist between actors. For example, a 'Customer' actor can have a more specialized actor called 'Corporate Customer,' which inherits behaviors but adds unique characteristics like monthly billing.

How can you test if a generalized relationship is valid in UML?

You can test the validity of a generalized relationship by asking if the child is a type of the parent. For example, 'Is a corporate customer a type of customer?' If the answer is yes, the relationship is valid.

Why can't you generalize between actors and use cases in UML?

You cannot generalize between actors and use cases because they represent different concepts. For example, asking if a 'Corporate Customer' is a type of 'Transaction' doesn't make sense, as one is an actor and the other is an action.

What happens if a child use case is identical to the parent use case in UML generalization?

If the child use case is identical to the parent use case, there's no need for generalization, as it wouldn't add any new information or behaviors.