IMPLEMENTED:
1) Every concept must have a prefLabel
2) Nothing can have two prefLabels in the same language
3) Every prefLabel must have a non-null language tag
4) Every concept must fall under (via skos:brooader) some concept that is the top concept of some concept scheme
5) No circularity in broader relations
6) Definition begins with lower case letter and does not end in period.
PROPOSED:
7) No concept can have an altLabel that matches any prefLabel.