Aaron, Martin, Thanks for creating the UML schema! It's very useful to start a discussion. I have two questions. First, what is the differences between Network and Domain? [1] It was discussed today, but couldn't really understand the details by phone. Second, the relation Link-Port in PerfSONAR is different from the relation Link-Interface in NDL [2]: in PerfSONAR it is many to one, while in NDL it is one to many. So, I understand that a Port in PerfSONAR can be connected to multiple links, but a link can only have one Port. I don't really understand. Can you give me an example? In NDL, a Link can have multiple Interfaces (typically 2). An interface is a logical interface, that is only connected to one link. If there would be multiple links, we would describe that with multiple (logical) interfaces (or with a BroadcastSegment). Regards, Freek [1] The difference between NetworkDomain and AdminDomain in NDL is that a NetworkDomain is a collection of network resources, while an AdminDomain is a collection of people (= an organization!): the people or organization that is responsible for managing the resources. The resources of an AdminDomain are not limited to network resources, but could also include CPU, storage, vizualization, services, etc. [2] A Link in NDL is a special case of a BroadcastSegment: a broadcast segment with exactly two interfaces. -- Disclaimer: This is an e-mail message. Use your own judgment about its value. If you do not have such common sense (e.g. you are a lawyer) or like to see crap like warranties, intended-audience or as-is statements, then the following applies: you do not understand the concept of satire and are not allowed to read this e-mail.