[Nexus] NXdetector questions (repost)

[Timothy Kelley]

Hello,

I'd like to repost some earlier questions about NX classes. If anyone 
can offer any insight, I would appreciate it. If these questions are 
meaningless or groundless, or if there is a better place to raise these 
questions, please let me know.

We are attempting to create a data file template for the ARCS 
spectrometer, and encountered some ambiguities in storing metadata. We 
want to have no duplication and no implicit definitions of metadata. You 
can see a draft version of our data file at:

http://wiki.cacr.caltech.edu/danse/index.php/XML_template_for_ARCS_data_files

While I had questions about a number of classes, I wanted to start with 
just one class: NXdetector.

My principle question is, how do we describe a composite detector like a
linear PSD. Many of the fields in NXdetector, such as <id>, are
presented as arrays of length i.
1) Is <id> meant to be an array of the id's of the composite's children?
1.a.1) If so, where do I put the id for the detector itself?
1.a.2) Does this mean all the other property arrays like gas_pressure
are meant to implicitly define the children? Wasn't nexus supposed to
get us out of implicitly defining things and into explicitly defining them?
1.b) If no, where do I put the children's id's, and why do I need arrays?

Or are NXdetectors meant to be nested? This would make
the hierarchy clear and lovely, but then why have arrays for everything?

Thanks,
Tim Kelley