Domainmodel:
    elements+=Element*;

Element:
    Aggregate | ValueObject;

Aggregate:
    'aggregate' name=ValidID ('extends' superType=JvmTypeReference)? '{'
        properties+=Property*
    '}';

ValueObject:
    'valueObject' name=ValidID ('extends' superType=JvmTypeReference)? '{'
        properties+=Property*
    '}';

Property:
    name=ValidID ':' type=JvmTypeReference;

valueObject Address{
}
aggregate Person{
    p : Address
}

@Check
def checkAggregateReference(Aggregate aggregate) {
    var properties = aggregate.properties

    for(Property f : properties){
        if(f is aggregate)
            error('An aggregate is not allowed to reference another aggregate'
                ,MdDslPackage.Literals.AGGREGATE
                ,f.eContainingFeature)
    }}
}