Class diagram makerfrom plain language, free.

classDiagram
  direction LR
  class Library {
    +String name
    +String address
    +addBook(Book book)
    +findBooks(String query) List~Book~
  }
  class Book {
    +String isbn
    +String title
    +String author
    +int year
    +isAvailable() bool
  }
  class Copy {
    +String barcode
    +CopyStatus status
  }
  class Person {
    <<abstract>>
    +String name
    +String email
  }
  class Member {
    +String memberId
    +Date joined
    +borrow(Copy copy) Loan
    +returnCopy(Copy copy)
  }
  class Librarian {
    +String staffId
    +approveLoan(Loan loan)
    +addCopy(Book book) Copy
  }
  class Loan {
    +Date borrowedOn
    +Date dueOn
    +Date returnedOn
    +isOverdue() bool
    +fine() Money
  }
  class Reservation {
    +Date placedOn
    +cancel()
  }
  class CopyStatus {
    <<enumeration>>
    AVAILABLE
    ON_LOAN
    RESERVED
    LOST
  }
  Library "1" o-- "*" Book : holds
  Book "1" *-- "1..*" Copy : has
  Person <|-- Member
  Person <|-- Librarian
  Member "1" --> "*" Loan : makes
  Loan "*" --> "1" Copy : for
  Member "1" --> "*" Reservation : places
  Reservation "*" --> "1" Book : for
  Librarian ..> Loan : approves
  Copy --> CopyStatus