Align Attribute and QueryContraint

[patrickkwang]

One of the main motivations for using an array of constraints for query graph elements was to align them closely with the attributes attached to knowledge graph elements. This is my understanding of how the two line up right now:

Attribute	QueryConstraint
attribute_type_id	id
original_attribute_name	name
value	value
value_type_id
	unit_id
	unit_name
attribute_source
value_url
description
	not
	operator

I think that the italicized fields do not need analogues, but many of the others should.

[patrickkwang]

I just discovered that @edeutsch has a somewhat different alignment in mind: #222 (comment)

Regardless of how they currently line up, this needs a good bit of attention.

[edeutsch]

I documented my understanding here:
#222 (comment)

It is nearly the same, but is different in a few subtle ways that are perhaps worth discussing at some point.
We pondered this alignment at the call last week. Agenda item 4g. But no changes were made after a little discussion.