VOConcepts paper

[Rob Seaman]

Another example is the characterization of filters for direct  
imaging.  For instance, the NOAO Mosaic camera team maintains a list  
of filters that includes both a long identifier - unique but hard to  
remember - as well as a short identifier, such as "R".  Each short  
identifier may correspond to several long identifiers, that is, to  
several individual filters.

If UCDs were used to create and track such lists, one could attempt  
to achieve the same many-to-one mapping by relying on the  
hierarchical nature of UCDs:   
filter.R.this_is_a_specific_wideband_R_filter.  This has problems on  
both ends.  First, there will often be a redundant prefix like  
"filter." and second, who is to say that it is the "R-ness" of the  
filter that we wish to capture in a short nickname?  Perhaps we  
rather need to capture the "wideband-ness" of the filter.  The  
problem with relying on a hierarchy in a single namespace is  
precisely that only one hierarchy exists per namespace.  On the other  
hand, multiple mappings are trivial with multiple namespaces.

The essential nature of a viable solution will be some mechanism for  
multiple authorities to maintain multiple non-local lists that permit  
such niceties as versioning.  In the absence of such a mechanism,  
separate projects will field separate, non-interoperable solutions.

The trouble with anecdotal examples is that they are too easy to  
gather.  The difficulty with this mechanism (whether realized as UCD  
namespaces or as RDF or as brute-force lists of aliases) will not be  
encountered when distinguishing between "stars" and "galaxies", but  
in the more obscure questions of art as referred to by George.

Rob
seaman at noao.edu