some remarks on VOEvent

[Ed Shaya]

Rob Seaman wrote:

> Roy says:
>
>> More properly we should *not* say VOEvent represents an  
>> astrophysical event, but rather it represents an *observation* of  an 
>> event.
>
>
> And "observation" is the default role to distinguish actual VOEvent  
> packets from tests and predictions.  It's the word "event" that is  
> shaky.  An astronomical event can extend vast distances and persist  
> over immense periods of time.  The observations that we're tracing  
> together as followup VOEvents may well involve detections of distinct  
> physical effects arising from disjoint regions of space-time.  We can  
> trust that causality ultimately ties it all together - but causality  
> is inferred, not observed.
>
   I'm afraid I don't get what you are flaming about here.  Why is it 
possible to define a VOEvent but not an event?
I thought the VOEvent is the VO publication of an observation of an 
ast:event.  So an ast:event is anything you would create a VOEvent 
about.  VOEvent is similar to an IAU-Circular which is the rapidly 
published information about an ongoing  rapidly developing event (or 
process if you want).  The circular is not the event, one needs to 
ontologicaly separate the two.  Because VOEvent is a publication it 
automatically inherits properties of a Publication such as 
DateOfPublication and Author (which may not be the same as the 
Observer).  These things would not normally be in the properties of an 
ast:event.

> One could argue that the semantic structure of a VOEvent is on a more  
> stable footing than the astronomical ontology we would hope to lean  
> it upon.  My point?  My point is that a single static astronomical  
> ontology is a vain hope - rather, we need a flexible mechanism for  
> building and extending a rich network of context dependent ontologies  
> as time and tide require.
>
Ontology allows one to use natural language to make statements and 
query.  The whole idea is to bring the flexibility of human language to 
machines (but perhaps to make it a bit clearer).  If you think this is a 
vain hope then why are you on this list?

> That's actually a good example that may illuminate these issues.  It  
> would be straightforward to describe a specific ocean tide  
> measurement in a VOEvent packet.  These are certainly observations of  
> astronomical events, after all.  Conjectures on tidal expressions in  
> astronomical ontologies?  Will these support generalized central  
> force representations?  And will they be expressed as spatial  
> derivatives of Kepler's or Newton's laws?  Or, rather, directly as an  
> inverse cube?
>
Ah.  So what you want is inflexibility.  You want to ensure that 
VOEvents do not have explanations of explanations or any other deep 
discussion of the event.   Indeed, OWL is not good for cutting off 
discussion.  It is always possible to make statements about statements 
and to extend classes on the fly.  XML Schema is much better for 
defining specific hard to alter structure.  So that is fine.  If the VO 
wants hardwired structures it should study the issue with Ontologies 
(because only in ontologies can you see the big picture with 
relationships between all of the components of the langauge)   and then 
use that as a starting point for creating limiting UML or Schema.

However, if one day there were a tide that went around the earth that 
was two time larger than any previously recorded tide,  I for one would 
like to see hypothesis and the detailed explanation of these with 
discussions of spatial derivatives and wave equations as soon as 
possible.  VOEvent might be a mechanism to spread this as rapidly as 
possible.  You might argue that there are no applications that could do 
anything with such details, but we are working on that too.

Ed

> Rob