Following script for an experimental db models several books, each of
which can have various number of genres, authors, publishers, etc.
Sample query is shown near end. Downloadable db at
www.xdb2.com/example/ex110.asp

// Create items in directory to classify things.
(CREATE *book.item ~in = dir)
(CREATE *ISBN.item ~in = dir)
(CREATE *author.item ~in = dir)
(CREATE *publisher.item ~in = dir)

// Create genres known at design-time.
(CREATE *genre.item ~in = dir)
(CREATE *fiction.cls = genre)
(CREATE *non-fiction.cls = genre)
(CREATE *sci-fi.cls = genre)
(CREATE *mystery.cls = genre)
(CREATE *computer.cls = genre)
(CREATE *database.cls = genre)

// Create a book with 1 author, 1 publisher, 3 genres.
(CREATE *Intro to Database Systems.cls = book
& it.ISBN = +0-201-54229-X
& it.author = +C J Date
& it.publisher = +Addition-Wesley Publishing Co
& it.genre = non-fiction
& it.genre = computer
& it.genre = database)

// Create a book with 1 author, no ISBN and 1 publishers.
// Classify book in a new genre created on the fly.
(CREATE *Symbolic Logic.cls = book
& it.author = +Susanne Langer
& it.publisher = +Vintage Books
& it.publisher = +Dover Publications
& it.genre = non-fiction
& it.genre = (CREATE *logic.cls = genre))

// Create a book with 2 authors and 2 publishers.
// Classify book in 4 genres,
// 3 of which are created on the fly.
(CREATE *Godel Esher Bach.cls = book
& it.ISBN = +0-39-74502-7
& it.author = +Douglas Hofstadter
& it.author = +Albert Einstein
& it.publisher = +Vintage Books
& it.publisher = +IDG Books
& it.genre = non-fiction
& it.genre = (CREATE *math.cls = genre)
& it.genre = (CREATE *art.cls = genre)
& it.genre = (CREATE *music.cls = genre))

// Find books written by C J Date in database genre.
// Finds "Intro to Database Systems"
(SELECT *.cls=book & *.author=C J Date & *.genre=database)