What are the hollow arrows in my .xcdatamodel?

I was looking through my .xcdatamodel and I noticed that there was an arrow that doe开发者_运维技巧sn't seem to represent anything(I can't post images so here's an example behind a link): http://s1.postimage.org/2ufcjo0jo/Screen_shot_2011_05_01_at_8_16_14_PM.png What does this represent? Thanks in advance.

Those arrows mean that one entity is a child of another. It goes from the child entity to the parent entity.