I said:
>> 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.
Rick Hessman says:
> The "cutting edge" will always be such that one won't have a useful
> classification scheme other than unusual combinations of the more
> general bits and pieces. That's why the UCD has to be hierarchical
> (to emphasize/extract general properties even when given specifics)
> and easily combined. Let's see.....
>
> cosmology.dark_energy <== cosmology.background;em.microwave
> cosmology.background.polarization;em.microwave
> stars.supernova.Type_Ia;process.eruption.hydrodynamic;
> process.eruption.thermonuclear
> galaxies.velocity_curve
> cosmology.abund
> ....
>
> (Aha - already discovered a few important UCD's to add....!)
I'm becoming more skeptical that IVOA standard UCDs are appropriate for representing the often slippery nature of astronomical "processes" and "objects". (As I pointed out at in a similar context at the VOEvent workshop - one might choose to regard an object simply as a long lived process. A main sequence star is a ~10 Gy thermonuclear reaction.) But a UCD is targeted differently (from UCD-1.9.9b):
"The Unified Content Descriptor (UCD) is a formal vocabulary for astronomical metadata that is controlled by the International Virtual Observatory Alliance (IVOA)."
The question is whether the characterization of astronomical objects/processes represents "metadata". The whole point of the precision of a UCD specification (e.g., phot.flux;em.optical;meas.error;stat.max) is to provide a solid foundation for building a sound scientific argument - but such an argument typically results in drawing new insights and building new logical connections - often using new vocabulary. On the other hand, even the most well established nomenclature regarding astronomical objects and processes is subject to revision and extension as better data and more profound theory collide.
Namespaces provide a possible way to address this. For instance, IVOA is developing a very basic namespace and various astronomical constituencies then support richer, and perhaps shorter latency, vocabularies of their own. However, we have this bit of constraining boilerplate to muddy the waters:
"4.1.2 Namespaces. The use of namespaces, indicated by the presence of a colon in theword is possible, but should be avoided as far as possible. The namespace is defined by the string before the colon and the word follows. The words in the non-standard namespace must be distinct from all words currently in the IVOA namespace. While developers may need local namespace, they should be used only temporarily, for words that are not yet included into the UCD validated by the IVOA. New words should be added using the procedures discussed in section XX."
What is the justification for trying to require that words in a non-standard namespace be distinct? For instance, we couldn't possibly require that two different non-standard namespaces not overlap. Why regard the IVOA namespace as *necessarily* preeminent? "Standard" does not equate with "compulsory". Either the standard makes sense or you won't be able to force folks to use it anyway. In any event, one would think that alternate interpretations of the same vocabulary would be one of the strongest justifications for alternate namespaces. This isn't an opportunity to lose control of alternate vocabulary - it's the way to enforce control of alternate usages. I also find the word "temporarily" to be curiously undefined for a science in which observations and inferences from decades and even centuries gone by may be revisited.
To the list of UCD commandments:
I might suggest adding:
8. For IVOA to control its vocabulary, it must provide the opportunity for others to control their own.
Ralph Waldo Emerson may shed some light:
"The poets made all the words, and therefore language is the archives of history, and, if we must say it, a sort of tomb of the muses For, though the origin of most of our words is forgotten, each word was at a stroke of genius, and obtained currency, because for the moment it symbolizes the world to the first speaker and to the hearer. The etymologist finds the deadest word to have been once a brilliant picture. Language is fossil poetry."
However much effort is expended to constrain and mandate standard usage, the users will seek ways to subvert the dominant paradigm. This isn't just the nature of users, it is the nature of science as poetry. Careful support for alternate usage is the key to controlling anarchy.
Rob Seaman
NOAO
Received on 2005-04-26Z18:21:06