working xtext entity exepct:

e.g
entity Book extends PublicationVenue {
	id title, // title of super-entity: PublicationVenue.title
	attribute publisher* : String,
	attribute isbn : String
}

works only with:
entity Book extends PublicationVenue {
	id PublicationVenue.title, // title of super-entity: PublicationVenue.title
	attribute publisher* : String,
	attribute isbn : String
}