Aaron and Martin, Thanks a lot for the UML schema. I just printed it, and will keep it under my pillow :-). A few questions. First of all, I don't fully understand teh difference between domain and network [1]. It was discussed, but not entirely clear by phone. Second, the relation Port-Link is different from our relation Interface-Link [2]. NDL has a many to one relation, while PerfSONAR has a one to many relation (the opposite). So in NDL, a (logical) interface can only be connected to ONE link (or one broadcast segment [2]). A link can have multiple connected interfaces (typically 2). Can you explain the situation for PerfSONAR to me? Can a port be connected to multiple links? How? Regards, Freek [1] The difference in NDL between AdminDomain and NetworkDomain is: NetworkDomain are simply grouping of *network elements*, while AdminDomain is a grouping of *people* (=an organization): the people or organization responsible for managing resources. The resources of an AdminDomain could include CPU, vizualisation, etc. Not just network elements. NetworkDomains can only include network resources. [2] Link in NDL is a special case of a Broadcast network: a broadcast network with two end points. I'll use the term Link for now.