problem cardinality

[elisa blasi <elisablasi@gmail.com>]

Hi all,
I don't understand the cardinality of CarrierParty and FreightForwarderParty in the ForwardingInstructions document, that is 0...1. 
 0..1 cardinality means that CarrierParty and FreightForwarderParty are optional fields. But CarrierParty and FreightForwarderParty are the receivers of ForwardingInstr. and I think that at least one of the two fields must be specified..
The only solution is to think that CarrierParty may be absent in the document when there is FreightForwarderParty : in this sense the cardinality of CarrierParty can be 0...1 ,and viceversa FreightForwarderParty may be absent in the document when there is CarrierParty ..but at least one of the two fields must be specified.. 
What is the meaning of this cardinality? Can you help me ??
Regards, elisa