Right now, we have two formats for representing a relationship.

When the relationship is being displayed in a response, it gets the full link-object representation:

"author": {
  "related": "", 
  "self": "",
  "linkage": ""
  //...
}

But when the relationship is being sent by the client to the server, only the contents of the linkage key are sent. So the format becomes: "author": { "type": "people", "id": "3"}.

It makes sense that creating/updating/deleting relationships is only doable through linkage, but do we really want the two separate formats?

Almost everywhere else in the spec we've gradually switched from preferring conciseness to preferring consistency. Why not do that here too?

If we did that, when clients sent a relationship, they'd specify:

"author": {
  "linkage":  { "type": "people", "id": "3"}
}

And the spec would simply say that these client-provided link objects MUST contain a linkage key.