[NeXus-tech] Dimensions in NXDL

[Akeroyd, FA (Freddie)]

There is a trac ticket for this
(http://trac.nexusformat.org/definitions/ticket/32) which we could use
for discussion, but it would mean everybody interested would need to
either join the nexus-definitions-tickets mailing list or add themselves
top the CC: of the above ticket

While we think about that, I'll mail a couple of initial ideas to
nexus-tech

What we want to be able to do is specify the dimensions of a quantity
and be able to reference it back to other quantities to, say, specify
that two arrays must be the same length. We may also want to be able to
restrict the size or specify exactly the size of a dimension.

Say in NXDL we had  

<field name="data">
<dimensions size="3"><dim3>5</dim3> </dimensions> </field>

This could specify a 3 dimensional array with the final dimension value
restricted to 5 


<field name="data2">
<dimensions ref="data" / >
</field>

This means data2 should have exactly the same dimensions as data1. How
far do we go in allowing references to fields in other groups?


<field name="data2">
<dimensions size="3"><dim1 ref="data" dim="dim2" /></dimensions>
</field>

This means that data2 should have dim1 the same size as dim2 in data


<field name="data2">
<dimensions size="3"><dim1 ref="data" dim="dim2" incr="1"/></dimensions>
</field>

As above, but   dim1 = dim2 + 1 (so allowing for histograms etc.)

These could then be converted into appropriate XML schema key/keyref
combinations.

Freddie 

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