Ontology-based queries

[Ashish Mahabal]

Tony wrote:

>On the other hand, if we modify the above query to be:

> Object is-of-type SNR
>  AND Source registers-in-wavelength X-Ray
>  AND Object is-within (1 arcmin) of-region (05 25 00 -69 38)

>I think we hit difficulties. I cannot see how an ontology-based query
>like this could work.

The above query is likely to be expanded out to:

 Object is-of-type SNR
  AND Source registers-in-wavelength X-Ray
  AND Object has-RA > x.y
  AND Object has-RA < z.w
  AND Object has-DEC > a.b
  AND Object has-DEC < c.d

But then, as you imply, the question of a subclass versus individual
objects would arise and the query may have to be split into two sections:
apples and oranges. Do just the first part first using an ontology:

 Object is-of-type SNR
  AND Source registers-in-wavelength X-Ray

and then on the resulting set do the SQL like query

select * where Object has-RA > x.y
  AND Object has-RA < z.w
  AND Object has-DEC > a.b
  AND Object has-DEC < c.d

However, if we can store the classes (SNR, X-ray) with an object along
with its attributes (RA, Dec), we could do the two in one fell swoop.

Whatever way is chosen, an important point to remember will be that the
query should magically rearrange itself so that the first clause is likely
to return the smallest number. Otherwise if we go through a large number
of objects only to throw away most of them at a later point, its a waste
of resources. But perhaps this point will come up much later.

-ashish

Ashish Mahabal, Caltech Astronomy, Pasadena, CA 91125
http://www.astro.caltech.edu/~aam aam at astro.caltech.edu

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