Hierarchies by attribute or by parent child -- why?

Discussion created by tomharr on Sep 30, 2014
Latest reply on Feb 18, 2015 by bill.leech1.4432149388399536E12
The "Market Value" diagram at shows item types that end up in Rally as Portofolio Epics and Features, and then User Stories in the lower level (non-portfolio level) of Rally.

Hiearchy: For User Stories, one builds the hierarchy by parent-child relationships. For Epics and Features, and assigning User Stories to Features, one builds the hierarchy by marking attributes (e.g. to put a User Story "under" a Feature, I mark that Feature value in the Feature field or attribute of the User Story. Similarly for putting Features "under" Epics in Portofolio in Rally.)

My question: why the difference in the way one represents hierarchy for the different types of items -- in some cases it's by attribute (putting parent item's value in field of child item) while in other cases (as far as I can tell, only with User Story objects), it's by marking the child as a child of the parent.

Why the difference, and what's its signficance?