If one of the requirements in a university system is that a teacher can update keywords of a subject, which class would get an operation "update Keywords"?单项选择题
A
Subject
B
Teacher
C
University
D
Keyword

Question

If one of the requirements in a university system is that a teacher can update keywords of a subject, which class would get an operation  "update Keywords"?

BlackTom AI · Accepted Answer

The class that should implement "update Keywords" is the one that owns and encapsulates the keyword data: Subject.

1) Relevant knowledge points and concepts
- GRASP Information Expert: assign a responsibility to the class that has the necessary information to perform it.
- Single Responsibility and cohesion: methods that change an object's own data belong to that object to keep behavior close to state.
- UML class vs. actor distinction: actors (e.g., Teacher) initiate actions but are not necessarily the place to put domain operations; domain classes hold domain behavior.

2) Step-by-step reasoning
- Identify who stores the keywords: a Subject class typically has an attribute like keywords (a list/set of Keyword objects or strings).
- Determine which class has the necessary information to modify them: Subject already knows its current keywords and any invariants (e.g., no duplicates, max count).
- Apply Information Expert: because Subject possesses the keywords, it is the expert on changes and should provide an operation to update them (add/remove/replace).
- Consider alternatives: a Teacher is the actor performing the change in the use case, but does not own the Subject’s internal keyword state. University is a higher-level container and would create unnecessary coupling if it directly manipulated a Subject’s internals. Keyword represents a single keyword entity/value and cannot by itself update the collection of keywords for a Subject.

3) Intermediate logical steps shown
- Subject.keywords exists → needs modification support → operation belongs to class with that data.
- Teacher triggers update in the system (e.g., calls Subject.updateKeywords(...) or a controller which delegates to Subject) → separation of actor and domain responsibility preserved.

4) Why the correct answer is correct
- Putting updateKeywords in Subject preserves encapsulation, keeps logic where the data is, follows Information Expert and SRP, and results in lower coupling and clearer ownership of behavior.

5) Why other options are incorrect (brief)
- Teacher: actor, not the data owner. University: overly broad container, violates cohesion. Keyword: represents single keyword, not the collection owner.

Conclusion: The correct class to receive the "update Keywords" operation is Subject, which matches the provided answer (Subject).

If one of the requirements in a university system is that a teacher can update keywords of a subject, which class would get an operation "update Keywords"?单项选择题

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