Feature/equivalent properties

[zonotope]

Closes #453

[dpetran]

Just to summarize my understanding of how this works:

When we're adding vocabulary flakes, if we see equivalentProperty we will add an entry for both the predicate and its object to our schema map. Then during query time we will check if the predicate has any equivalent properties and resolve the flakes for those predicates as well.

Looks good!

[zonotope]

Just to summarize my understanding of how this works:

When we're adding vocabulary flakes, if we see equivalentProperty we will add an entry for both the predicate and its object to our schema map. Then during query time we will check if the predicate has any equivalent properties and resolve the flakes for those predicates as well.

Looks good!

That's right. There's one additional nuance where we also make sure to add entries to the schema for all the other predicates already defined to be equivalent for both the subject and object of the equivalent property flakes. That ensures that if someone says that a is an equivalent property b, and later that b is an equivalent property of c, then the system also treats a as an equivalent property of c.

The last assertion in the fluree.db.query.property-test/equivalent-properties-test checks for this.