import 'platform:/plugin/org.eclipse.emf.examples.library/model/extlibrary.ecore'

package extlibrary

context Library
-- get all books with a title in a library and its branches (recursively)
def: getBooks(title : String) : Set(Book) =
    books->select(b | b.title = title)->asSet()->union(
        branches.getBooks(title)->asSet())

context Book
-- the library containing a book
def: library : Library = Library.allInstances()->any(books->includes(self))

-- book titles are unique within their library branch (and its sub-branches)
inv unique_title: not library.oclIsUndefined() implies
     library.getBooks(title) = Set{self}
 
endpackage