How to make pivot models / rich relationships / edges in Atomic Data #132

We often want to provide more information about the relationships between resources:

• Say I want to describe the friendship between two people. I could create a friendship Property that simply points from one Person to the next Person. But what if I want to describe details about this friendship, such as when it started?
• Alice is a Manager at AcmeInc. Her role is what connects her relationship to the organization.

In labeled property graph databases, you'd probably model these in an edge. In Atomic Data (and RDF), relationships can't have their own properties.

This means we need a pivot model.

• The friendship, for example, could have a from and to attribute, as well as a startDate.
• The role could have an person, organisation, roleType, and startDate

Some questions about this:

• How do we deal with relationships where the from and to are really no different? Using two different properties is confusing, and makes it harder to perform queries (we need to run queries in both directions to answer any question). Do we us a links property that is a resourceArray containing a maximum of two resources?
• Should these relationships be instances of new Classes? In our examples, a Friendship and Role class would probably make a lot of sense. But maybe a more constrained model is more appropriate for these pivot type models?