@namespace(uri="library", prefix="")
package library;

class Library {
	val Writer[*] writers;
	val Book[*] books;
}

class Writer {
	attr String name;
	ref Book[*]#author books;
}

class Book {
	attr String title;
	attr int pages = 100;
	attr BookCategory category;
	ref Writer[1]#books author;
}

enum BookCategory {
	Mystery = 0;
	ScienceFiction = 1;
	Biography = 2;
}