[Nml-wg] Definitions for relations

Hi, I've just committed an updated version of the NML Schema document. This includes earlier changes from Freek. I have also committed definitions for several relations. There is one that I want to check with you: The \emph{Label} assigned to this \emph{Port} is the technology label that the traffic through this \emph{Port} has been assigned. This \emph{Label} is used to distinguish the \emph{Port} in a \emph{PortGroup}, or to define the traffic flow through a \emph{SwitchingMatrix}. Is that correct? For others I have added some text, or removed the TODO because the definition was already in the first description of the relation, and it is a too simple definition to expand further. Jeroen.