On 26 Apr 2005, at 4:20 pm, Rob Seaman wrote:
> On Apr 26, 2005, at 3:28 AM, Rick Hessman wrote:
>
>> I've added more VOEvent examples, several suggestions for IVOA/UCD to
>> the proposed
>> object/event/process UCD list at
>>
>> http://monet.uni-sw.gwdg.de/twiki/bin/view/VOEvent/
>> UnifiedContentDescriptors
>
> Good start at a list. A search facility would add immensely to its
> usefulness as the list grows. This would also function as a validator
> for an astronomer's guess as to the proper syntax for a familiar class
> of objects.
>
>> If something like this list has already been created, I'd appreciate
>> hearing about
>> it before I put much more work into our own.
>
> This would be a good opportunity for VO to reach out to the larger
> community. It really isn't for us to mandate nomenclature. An
> interactive dictionary/beastiary of astronomical objects and processes
> could be useful all by itself, and will be of obvious utility for
> various VO projects. A common understanding of each "hypothesis" will
> indeed be key to VOEvent, for instance.
On the other hand, one can't have TOO many people laying on their hands, since there is a need for some level of editorial control. We'd be happy to provide our Twiki more-or-less as it is, since it's already interactive and available to anyone interested.
> I'm not sure, however, that the ApJ keywords are the best model for
> constructing this content descriptor list. Keywords are a way to
> partition the level of interest a member of the community may have in
> reading a paper. A UCD is a way of partitioning the underlying
> physics. For instance, given that the interest in working on this is
> arising out of VOEvent, it isn't surprising that there is a focus on
> processes more than objects, and that the selection of objects would
> be weighted toward time variability in various ways. There are dozens
> of fine shadings between variable stars. On the other hand, while one
> can distinguish between elliptical, irregular and spiral galaxies,
> there isn't any mechanism (yet) for specifying the precise type of
> each.
Actually, the ApJ/A&A/MN keywords should really be a GREAT place to start, since they are supposed to capture what is eventually done with the content. It's clear that they don't provide a uniform and uniformly deep level of description, but at least they provide a good and evenly distributed place to start.
> I'm leery of encouraging these descriptors to become longer than they
> are, but it seems inappropriate to specify generally descriptive
> classes, like:
>
> stars.variable.irregular
> stars.variable.long_period
> stars.variable.semi-regular
>
> at the same level as members of prototypical classes, like:
>
> stars.variable.Cepheid
> stars.variable.RR_Lyr
> stars.variable.RS_CVn
>
> (And where is stars.variable.W_UMa? Just pointing out that the list
> will never be complete.)
> Perhaps it should be stars.variable.class.Cepheid? Or better yet,
> adjust in the other direction, maybe stars.variable.period.irregular?
> Or ideally, a general mechanism might be provided for parametrically
> classifying periodicity.
No no no no : these are individual stars but names commonly used to typify a certain variable star behavior (just as we say "Cepheids" and really mean "delta Cepheids" = "stars like delta Cep"). There really are "W UMa" stars. Of course, the UCD can't be defined for individual objects other than a very few like the Sun, Moon, and major planets. Thus, "stars.variable.W_UMa" means the same as "stars.variable.class.W_UMa"; I suppose we could add on the "*.class*" just as a reminder, but at the cost of an additional hierarchical level of detail.
> The challenge here is not only that the list will never be complete,
> it is that we should be encouraging researchers to actively augment
> and improve the list. A workable classification scheme is often the
> first step in organizing a research program. But the result of a
> research program is often to overturn the original classification
> scheme. We don't want to provide a mechanism that is only useful for
> describing objects far removed from the cutting edge.
Fortunately, astronomers - even very good ones - are often rather traditional in their use of nomenclature, so we'll need such metadata whether someone thinks it's quaint or not. As a stellar astrophysicist interested in variability and accretion, I've included things I'd like to have and will leave it to others to include their own metatdata.
Rick
Dr. Frederic V. Hessman Hessman-at-Astro.physik.Uni-Goettingen.DE Universitaets-Sternwarte Tel. +49-551-39-5052 Geismarlandstr. 11 Fax +49-551-39-5043 37083 Goettingen http://www.uni-sw.gwdg.de/~hessman ------------------------------------------------------------------------ -------------------------
http://monet.uni-goettingen.de ------------------------------------------------------------------------ -------------------------Received on 2005-04-26Z14:43:51