Clarification in docs needed on whether two IfcRelConnectsPorts are allowed for a port.

IfcRelConnectsPorts suggest that the RelatingPort is the source and the RelatedPort is the sink:

> For port connections between elements, the RelatingPort is set to a port having FlowDirection=SOURCE and the RelatedPort is set to a port having FlowDirection=SINK.

However, what happens if the FlowDirection=SOURCEANDSINK for both ports?

Option 1: Does this mean that the order of RelatingPort and RelatedPort is arbitrary?
Option 2: Or does it mean that we should have _two_ IfcRelConnectsPorts? One pointing one direction, and the other pointing the other?

If option 1: the benefit is that you have less Rel entities to manage for the one connection. It also decouples the semantic meaning of RelatingPort=SOURCE and RelatedPort=SINK and the flow direction which could very well change or be recalculated later. For analysis, typically first a connection is made, then the direction is determined. Right now, determining the relationship means that you'd potentially have to switch the attributes.

If option 2: the benefit is that you can recursively traverse ConnectedTo (or ConnectedFrom, if you're going the other way) relationships to go through a model without writing complex "If FlowDirection=="SOURCEANDSINK" then ..." logic. It makes finding upstream or downstream objects in a system easier.

It would be good to decide on the preferred convention and to document it explicitly.