some semantic puzzles from VOEvent

[Rob Seaman]

On Jun 6, 2005, at 7:31 AM, Bernard Vatant wrote:

> nobody has found so far a consensual definition of what an human *is*.

Actually, we have an excellent operational definition of "human" (in  
its meaning as a synonym for Homo sapiens).  A human is an  
interbreeding (hypothetically or actually) descendent of humans.   
Combine that rule with an example entity deemed to be human and stir  
inductively.  The point here is that evolution serves as a unifying  
force in constructing biological ontologies.  Astronomy has no  
similar unifying conceptual framework above the level of fundamental  
physics.

> even more simple questions are tricky : what is the minimal size  
> for a planet? for an asteroid? for a comet? Every value would be  
> arbitrary, although nobody I guess would call a body of mass a few  
> grams orbiting the Sun a planet ... All those issues boil down to  
> the good old undecidable question "What is the minimal number of  
> grains to make a sandheap?"

Yes, but I question your assertion that these questions are  
undecidable.  The literature is rife with variations on ways to  
express size distributions (e.g., initial mass functions) that would  
allow capturing such subtleties.  Does "natural language" include the  
mathematical expressions that are the natural way to express so many  
astronomical concepts?  Does knowledge engineering extend to actually  
expressing an HR diagram - or would Ejnar and Henry simply have to  
describe the main sequence in prose - or perhaps poetry?  "I think I  
shall never see, a poem as lovely as the asymptotic giant branch."

Rob