some semantic puzzles from VOEvent

[Rob Seaman]

Bernard Vatant comments on Roy's VOEvent issues:

> (1) [...]  We would like a formal vocabulary so that, for example,  
> the computer can understand that "Supernova" and "SN" are the same  
> thing. However, my simple attempts to do this as a new branch of  
> the UCD tree blew up into a storm of controversy. How can we make  
> progress here?

>> everybody knows (or thinks so) or at least implicitly agrees upon  
>> what Jupiter *is* and looks like, what a planet *is*, and so on.  
>> There is a unique (implicit) interpretation in the common  
>> (implicit) ontology.

"Jupiter" is a proper name for a specific entity.  That  
identification is simply a definition under the control of the  
appropriate IAU committee or some other international body.  There is  
intrinsic ambiguity, however, with the definition of classes of  
objects - with nouns that don't correspond to proper names.  What is  
a planet?  What is a gas giant?  For many purposes the answers to  
these questions are obvious, something like: a gravitationally bound  
non-stellar entity orbiting a star.  (Although it quickly becomes  
obvious that all definitions depend on other definitions.)  For other  
purposes, such as the characterization of planetary atmospheres or  
magnetic fields, the precise transition from Jupiter to  
interplanetary space may be hazy indeed.

As far as the storm of UCD controversy - isn't that where the fun  
is?  My characterization of Rick Hessman is that he will pursue his  
<Concept> factory whether or not it is associated with UCDs or other  
VO standards.  The only controversy is to avoid splitting the  
development tree :-)

> (2) [...] One report says the Event is a Supernova, another says it  
> is a SupernovaType1a, another says it is a SN and another says  
> "bright source associated with a galaxy". Are these four in agreement?

>> Observer X has taken an image later interpreted as being a SN 1c  
>> in NGC 4038. Other, looking to the same sky
>> coordinates, have obtained other data that they interpret as being  
>> images of the "same" object in the "same" galaxy (whatever this  
>> "sameness" actually means ...).

I presume synonyms such as "Supernova" and "SN" will be trivial to  
handle.  Less trivial might the the example at the bottom of section  
3.7 of the VOEvent specification.  The object or process that has a  
proper name of "Tycho's Stella Nova" is classified as "SN 1a".  An  
assertion is made that this is associated with the object/process  
called "3C 10" which is classified as a "supernova remnant".   
Astronomy abounds with famous objects for which large numbers of  
reliable identifications and classifications of various sorts are  
available.  We are more interested in how to classify the question  
marks - in precisely the terra incognito of the emerging ontological  
maps.  A description of the science that was current last year is not  
going to prove exceptionally helpful.  A successful ontology will be  
one that includes an easy process for growth and hypothesis.

> (3) [...] If I have a lot of VOEvent packets that refer to the same  
> astrophysical event, can I extract a SED or light-curve (or time- 
> dependent SED) by federating all the separate observations?

>> As long as you put together data from different sources, the  
>> agreement about those data being about the same thing supposes an  
>> (there again, most of the time implicit) agreement on a world  
>> model where this object is supposed to "exist".

I think the issue here is broader than VOEvent.  VOEvent is a  
mechanism for alerting systems and personnel to transient events.  A  
VOEvent might well trigger a VO query that would result in the  
generation of a light-curve or SED.  These secondary data products or  
inferences might then generate a followup VOEvent aimed at producing  
further observations to confirm or extend some resulting hypothesis.

Rob Seaman
NOAO