private static EntityProperty CreateNavProperty(XElement element, XContainer document)
        {
            var relationship = element.Attribute("Relationship").Value;
            var association = document.Edm()
                .Descendants("AssociationSet")
                .Single(ae => ae.Attribute("Association").Value == relationship);

            return new EntityProperty(
                association.Attribute("Name").Value,
                EntityPropertyType.NavigationProperty);
        }