By cisco Service policy is a policymap that is being attached to a logical interface. Fist what come in to me mind create class PolicyMap which have relation with IpInterface and use separate modeler plugin. ServicePolicy (Cisco) object contain folowing information
'.4': 'cbQosIfIndex', #Index of Interface to which PolicyMap attached
But i can't find way to tell modeler to which interfacce apply this information. Mey be this is miss approach. I see another way, create relation OS - ServicePolicy and after that somehow bind ServicePolicy and Interface.