abstract Book// a template for a book

title -> string// a title can hold a text value

subtitle -> string ?// subtitle is optional

year -> integer// year has a numeric value

page 2..* // at least 2 pages

xor format// a book can be in only one format at a time

paper

hardcover ?// hardcover is optional and only makes sense when the book is paper

electronic

xor kind// a book can be of one kind at a time

textbook

manual

reference

fiction

nonfiction

other -> string// other allows giving a kind in text

author -> Author +// author points at least one author of the book

[ year >= 1970 => ISBN ]

ISBN -> string ?// it is currently not possible to specify in Clafer that ISBN has 10 digits

GS1 -> string ?

[ year >= 2007 => GS1 ]

GenerativeProgramming : Book// author is a special person who has at least one book

[ title = "Generative Programming" ]// book has to point at least one concrete book

[ year = 2000 ]

[ # page = 589 ]// a concrete example of a book

[ paper ]

[ author = Czarnecki, Eisenecker ]// number (#) of instances of page is 589

[ ISBN = "0201309775" ]// because the book is paper it automatically also has a format

Czarnecki : Author// because the book is nonfiction it automatically also has a kind

[ name = "Krzysztof Czarnecki" ]// Czarnecki and Eisenecker are the authors

[ GenerativeProgramming in book ]// there's no GS1 prefix, which is ok because the year is < 2007