Add chain rules for mappings

[cthoyt]

trafficstars

Mapping Chains

Transitivity of equivalence

• skos:exactMatch skos:exactMatch -> skos:exactMatch

Broad

• skos:exactMatch skos:broadMatch -> skos:broadMatch
• skos:broadMatch skos:exactMatch -> skos:broadMatch

Narrower

• skos:exactMatch skos:narrowMatch -> skos:narrowMatch
• skos:narrowMatch skos:exactMatch -> skos:narrowMatch

Nothing

• skos:broadMatch skos:narrowMatch -> no

TODO

• add more chains for related, like owl:equivalentTo? Or is it good enough to say these are the same as skos:exactMatch

@matentzn feel free to edit the issue in place for adding more