상황
A library system needs to model books, copies, members, librarians, loans, reservations, and fines with clear ownership and multiplicity rules.
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01
Separate Book (metadata) from BookItem (physical copy) to allow multiple copies and track status per copy.
02
Use composition for Library-Book and Book-BookItem, aggregation/association for member loans and reservations, and dependency for fine generation.
Use this diagram when designing a library circulation system, integrating with an OPAC, or modeling inventory and loan lifecycle.