Definitions

[Norman Gray]

Whoa, everybody -- I spend a day out of wireless range and come back  
to... this?

We are emphatically _not_ in the business of creating a dictionary of  
astronomy here.  Our job here is to take vocabularies that already  
exist, such as the A&A, AOIM or IAU-93 vocabulary, and SKOSify them.   
Nothing more.

If this process results in some ambiguities (and Ed and Brian have  
illustrated where those might be), then that's just hard luck.  Those  
ambiguities will remain until someone who is materially affected by  
the ambiguities can make a case to expend resources on producing  
updated vocabularies, and ideally a full-blown ontology, with the  
ambiguities removed.

That means that the IAU-93 term 'ABSOLUTE MAGNITUDE' will turn into

<#AbsoluteMagnitude> a skos:Concept;
     skos:prefLabel "Absolute magnitude"@en, "Magnitudine assoluta"@it;
     skos:definition "Absolute magnitude"@en.

Not very exciting, I know, but it's all we've got, and if we try to  
add fuller definitions we will talk and talk and talk and produce  
nothing.  Also, as Rob has mentioned more than once now, we don't have  
the authority to start adding fuller definitions.  (By the way, I  
think I misunderstood Brian's recent question about definitions and so  
didn't answer usefully: Yes, we need skos:definition properties to be  
present; no, we can't afford to expand these definitions as much as  
we'd possibly like; sorry for any confusion).

Brian asserts that a messy vocabulary will be fairly useless for  
practical applications.  But the use-cases in the document are  
practical applications, and they can be satisfied with occasionally  
imprecise vocabulary terms.  If these use-cases are inappropriate,  
Brian and everyone, then let us know, because the document is aiming  
at satisfying those, and not others.

Remember that the terms in the A&A vocabulary have no real definitions  
at all, but they've been used for some years now without the sky  
falling down, because the terms are _clear enough_ for their intended  
purpose.





I've added text to the beginning of the document which I hope  
clarifies the scope.  Comments on that are welcome.

We've rehearsed a variety of opinions about definitions here; I doubt  
it would be useful to rehearse them again.  If anyone disagrees with  
the text in the document as it stands can you phrase the disagreement  
as an issue, summarising the alternative points of view, and I can add  
it to the outstanding list.  Remember that <http://www.astro.gla.ac.uk/users/norman/ivoa/vocabularies 
 > will be the most up-to-date built version, in between 0.x releases,  
and <http://www.astro.gla.ac.uk/users/norman/ivoa/vocabularies/issues>  
is the issues list.

All the best,

Norman


-- 
Norman Gray  :  http://nxg.me.uk
eurovotech.org  :  University of Leicester