import 'platform:/resource/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