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Abstract Classes:

plaintext 
Class LibraryItem
+ id: String
+ title: String 
+ available: Boolean 
+ checkOut(user: User): void 
+ returnItem(): void 
+ calculateFine(daysLate: int): double

Class User: 

+ userId: String 
+ name: String 
+ contact: String 
+ borrowItem(item: LibraryItem): void 
+ returnItem(item: LibraryItem): void 
+ payFine(amount: double): void

Inherited Classes:

plaintext Class Book extends LibraryItem 
+ author: String 
+ genre: String 

Class DVD extends LibraryItem 
+ director: String 
+ duration: int 

Class Patron extends User 
+ borrowedItems: List<LibraryItem> 

Class Librarian extends User 
+ manageItem(item: LibraryItem): void 
+ registerUser(user: User): void