Taxonomy issues

[Tony Linde]

Thanks, Anita. 

> So we will have to allow an object to be multiply classified.

No problem with that if the classifications are not mutually exclusive,
ie you are simply locating the object along multiple, orthogonal axes.

> There are a few classifications which one might naively want 
> to make exclusive e.g. elliptical or spiral, Seyfert 1 or 
> Seyfert 2 (or more complex sub-groups).

The problem could be where an object sits on the boundary between two
classes. One observer may classify it one way and another the other way,
simply because their analyses of the data are based on two different but
equally respectable techniques.

> Do you think it would work to have a 'security of 
> classification flag'? 

Should be possible, but we would have to discard any idea of mutually
exclusive classes from the ontology which could make checking new
classifications rather a waste of time.

I wonder how the bioinformaticians handle this?

> Or do the search at the time of query - for each object found 
> classified as an elliptical, check it is not also classified 
> as a spiral.

But allow user to specify whether such objects are or are not used. Yes.

Cheers,
Tony. 

> -----Original Message-----
> From: owner-semantics at us-vo.org 
> [mailto:owner-semantics at us-vo.org] On Behalf Of Anita Richards
> Sent: 27 September 2002 16:39
...
> Is a matter of how we restrict the classification classes 
> within an ontology? There are some multiple definitions which 
> are not due to disagreements anyway, and there is also the 
> important point which older astronomers tend to be more 
> careful about, which is that we don't really know what 
> anything is anyway (outside the solar system places where 
> probes have been), so really everything should be 'has the 
> appearance of'/'behaves like' or ' is in the direction of' 
> rather than 'is a' or 'is at' 
> but most of us are more definate just because it is shorter....
> 
> but for example, a galaxy can have multiple names (NGC 6xxx = 
> Markarian 348 = ...), it can a starburst galaxy and a ULIRG 
> (ultra-luminous IR
> galaxy) and a megamaser galaxy (producing bright line 
> emission) and a Seyfert 1 and a spiral....
> 
> So we will have to allow an object to be multiply classified.
> 
> There are a few classifications which one might naively want 
> to make exclusive e.g. elliptical or spiral, Seyfert 1 or 
> Seyfert 2 (or more complex sub-groups). However the problem 
> you raise suggests this would be a bad idea unless there is a 
> very good reason for doing so.  And I think we can have 
> multiple descriptions?  e.g. a car can be both 'red' and 
> 'sports' in the example the Manchester Computing people showed us.
> 
> The trickier question is how we respond to queries, e.g. 
> suppose one catalogue classifies Gridlock A (the brightest 
> radio source in a new constellation named after AstroGrid) as 
> an elliptical, another classifies it as a spiral and the 
> automatic classification routine which we run on Sky Survey 
> plates says it is an irregular.
> 
> If someone says 'what is Gridlock A' we can give them all 3 (or more
> definitions) with references.
> 
> But if someone says 'give me all the ellipticals in Gridlock 
> A' what do we do?  (actually, this is the sort of thing which 
> someone  raised at TIVO, if you look for outliers, for every 
> one interesting and unique object you may get 10 or 100 
> misclassifications/measurement errors..)
> 
> Do you think it would work to have a 'security of 
> classification flag'? This would have to involve some sort of 
> check-list of contradictory classifications - a 'contrdiction 
> exists' property?
> 
> This could work two ways:
> When a catalogue is contributed, check objects with these 
> classifications against existing entries and flag those with 
> contradictions.  Of course, this does not mean that an 
> uncontradicted classification is correct...
> 
> Or do the search at the time of query - for each object found 
> classified as an elliptical, check it is not also classified 
> as a spiral.
> 
> Either way initially the VO could just give a contradiction 
> flag and a reference.  Eventually we could in some cases give 
> an estimate of reliability based on e.g. catalogue 
> resolution, sensitivity, age, or even some VO panel of 
> experts for very large or significant catalogues (in the 
> way that at present we would have a heirachy of position 
> accuracy catalogues, starting with Hiparchos and finishing 
> with the Almagest (or maybe gamma ray catalogues...).
> 
> (For stars it is worse, as they should not be e.g. both 
> spectral type A and G at the same time, and if they are that 
> implies either a mistake or a binary.  But in the case of 
> measurements taken many years apart it could mean it has 
> evolved.  Galaxies don't evolve that fast (but they could 
> have companions within the field of view I suppose...).
> 
> cheers
> a
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
> Dr. Anita M. S. Richards, AVO Astronomer
> MERLIN/VLBI National Facility, University of Manchester, 
> Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL, 
> U.K.           
> tel +44 (0)1477 572683 (direct); 571321 (switchboard); 571618 (fax). 	
> 
> 
> 
>