Describe the model of the library. There are 3 entities: 'Author', 'Book', 'Reader'. Physically, there is only one book and it can only be with one reader. Create tables for the library considering this. A book can have multiple authors.

To describe a library model with entities "Author", "Book", and "Reader", considering that:

• Physically, there is only one book copy and it can only be with one reader at a time.
• A book can have multiple authors.

The following tables can be proposed:

-- Authors table
CREATE TABLE Authors (
  AuthorID INT PRIMARY KEY,
  Name VARCHAR(255) NOT NULL
);

-- Books table
CREATE TABLE Books (
  BookID INT PRIMARY KEY,
  Title VARCHAR(255) NOT NULL
);

-- Readers table
CREATE TABLE Readers (
  ReaderID INT PRIMARY KEY,
  Name VARCHAR(255) NOT NULL
);

-- Junction table for authors and books (many-to-many)
CREATE TABLE BookAuthors (
  BookID INT,
  AuthorID INT,
  PRIMARY KEY (BookID, AuthorID),
  FOREIGN KEY (BookID) REFERENCES Books(BookID),
  FOREIGN KEY (AuthorID) REFERENCES Authors(AuthorID)
);

-- Table to track which reader has which book (one-to-one)
CREATE TABLE BookLoans (
  BookID INT PRIMARY KEY,
  ReaderID INT UNIQUE,
  LoanDate DATE,
  FOREIGN KEY (BookID) REFERENCES Books(BookID),
  FOREIGN KEY (ReaderID) REFERENCES Readers(ReaderID)
);

Here, BookLoans guarantees that each book can only be loaned to one reader at a time, and a reader can have at most one such book (if multiple books per reader are allowed, remove the UNIQUE constraint on ReaderID). The BookAuthors table implements the many-to-many relationship between books and authors.