Closure tables are new to me as well. If you're interested in encoding hierarchies in relations, I took a look at static trees and binary fractions in particula

Closure tables are new to me as well. If you're interested in encoding hierarchies in relations, I took a look at static trees and binary fractions in particular here: http://seespotcode.net/2016/04/30/static-trees/ http://seespotcode.net/2016/04/30/static-trees/ It's got some pretty serious practical limitations, but I found it an interesting exploration.