Gives content access permissions to users for content that references the users with User reference or Entity reference.
This is great if you want your content authors to be able to choose additional authors, or choose who can view their content, as well as being able to display the list of authors or viewers within your content, or in views displays.
the 'right way' to do this is to work with entity approach and avoid the ['und'][0] business but I never got it to work in views. i.e. code $node=menu_get_object(); $field = field_get_items('node', $node, 'field_event_artistref'); return field_view_value('node', $node, 'field_name', $field['target_id']); code. Here's a link I was following on the topic computerminds.co.uk/articles/…
Relation is not a field, but an entity in itself. It can store directed but also non-directed relations. It can store as many entities as you want, so storing all five Marx brothers is easy. And, relation is not just simply an entity but a fieldable entity