Mandatory Global Attributes

[Chris Moreton-Smith]

At the risk of being pedantic, I think it's worth saying that when Freddie 
asked me if there was a list of global attributes somewhere I looked at the 
summary of the SoftNeSS'96 meeting and got them from paragraph (8) where it 
says

	"Each NeXus file will have the following global attributes:"

which seems like a fairly mandatory definition!

Trying to remember the discussion I think it centred around the need to have 
some fixed/guaranteed attributes which would be very easy to locate and could 
easily be dragged out of ANY NeXus file. Probably to put in an index file, a 
database or used by a searching program to identify misnamed files (this we 
have had to do before with ISIS raw files when problems have caused them to be 
misnamed).

Obviously if the attributes are not mandatory and not generated automatically 
by NXOpen any indexing program would have to check for the existence of 
attributes which might or might not be there and the facility becomes rather 
less useful!

We have several options:

1) Drop the mandatory attributes altogether
2) Make NXOpen GENERATE the fields but put nothing in them (at least they are 
guaranteed this way).
3) Put machine generated content in them as far as is possible - eg from 
finger.
4) Prompt the user to set them
- perhaps by a warning on the first attempt to write data when the attributes 
are still blank
5) Return to the six parameter solution (just an antidote to possibly 
questionable machine generated parameters).  This does seem slightly clumsy but 
after all, NXOpen isn't going to get called that often.

I don't have any strong feelings on this either way so I'm happy to leave it to 
the interface group to choose.

	Chris

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