VDOM Basics

Apologies if this question seems too simple but I'm confused by the exact nature of a FortiGate VDOM.

1) On a Fortigate (in this case a FG1000D) if you create two separate VDOMS must you assign a separate physical Fortigate port (or ports) - plus separate cables to other network devices - to each VDOM?

or

Can you just, in it's simplest case with 2 separate VDOMs - have one physical port (for example, either one of the two 10GB SFP+ ports or an RJ45 1GB Ethernet port) plugged into the physical FG1000D and then virtually assign different interfaces to each VDOM?

(I guess what I'm asking is from the physical FG100D do you have to associate at least one physical port and cable to each VDOM?)

2) My second question is - what's the relationship, if any, between a 'VRF' and a FortiGate VDOM?