Scope relationship constraints to a set of node types

[beechnut]

Background

A person can know another person, and a person can also know a skill, fact, or topic.

If a person knows someone, they probably know each other, so you could set reciprocal: knows.

However, if a dataset says that someone knows a person and also knows a fact, then the dataset with the reciprocal setting will say that the fact knows the person! That's not right.

We should be able to scope relationships by setting what node types apply to a given rule.

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Here are plain English descriptions and its Aspen discourse translation.

knows relationships between people are reciprocal, but those between a person and anything else (e.g. a fact or skill) is directed.

reciprocal: knows (Person to Person)

knows relationships are allowed between a Person node and any other node.

allow_only: knows (Person to *)

knows relationships are allowed between a Person and a Person, or between a Person and a Skill.

allow_only: knows (Person to Person, Person to Skill)