One of the advantages of Jangle is that it gives every discrete resource exposed a unique URI with a modicum of permanence.
However, the Jangle connector should not be expected to know the absolute URI of any of its resources, since that is at the discretion of the Jangle core application to manage. In fact, it's conceivable that a Jangle connector's resources could have multiple URIs for the same resource, if, for example, a connector is proxied by multiple Jangle core applications.
This means that a Jangle core must be able to handle both relative and absolute URIs in a connector response (since a connector response could refer to a resource defined in another service, which would need to be explicit).
It makes sense, then, that, for simplicity's sake: URIs to resources within a given connector should be relative (i.e. /resources/12345) and URIs external to a service absolute (i.e. http://jangle.org/otherservicename/resources/12345)