What does TOP mean ?

[Arnold Rots]

No, it's not global, but applied to the datasets that satisfy the query.
Though instrument and exposure time do not change, the off-axis
parameter does. In the case of a cone search, for instance, it is
the angle between the center of the cone and the direction of the
optical axis.

  - Arnold

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Arnold H. Rots                                          Chandra X-ray
Science Center
Smithsonian Astrophysical Observatory                   tel:  +1 617 496
7701
60 Garden Street, MS 67                                      fax:  +1 617
495 7356
Cambridge, MA 02138
arots at cfa.harvard.edu
USA
http://hea-www.harvard.edu/~arots/
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On Mon, Apr 27, 2015 at 11:03 AM, Markus Demleitner <
msdemlei at ari.uni-heidelberg.de> wrote:

> Hi Arnold,
>
> On Mon, Apr 27, 2015 at 09:43:46AM -0400, Arnold Rots wrote:
> > Yes, you need an observatory-specific model to calculate a score.
> > By its very nature, therefore, it will only be a relative score.
> > Example:
> > For Chandra we implemented a score that is based on instrument, exposure
> > time, and off-axis angle
> > (PSF degrades with increasing off-axis angle).
>
> Well, yes, that could be part of it, but the way I understand
> things --
>
>   [...] the general idea is that the better a candidate dataset
>   matches the query, the higher the score it receives.  (1.1, P.27)
>
> -- TOP's intended function is essentially like Google's ranking: it
> gives "how well" a given returned row matches a data set.  Hence, for
> a given dataset score would be different for different queries, and
> while a global quality measure might play a role, it certainly
> wouldn't be expected to dominate the response.  Or am I completely
> off here?
>
> And regarding Walter's interjection:
>
> > I thought that the difference between MAXREC and TOP is that MAXREC
> > requires an overflow indicator, while TOP would prohibit it.
>
> Interesting thought -- is it intended to work this way? [it doesn't
> in DaCHS, and a quick search in the 1.1 specs didn't give me anything
> pointing in that direction]
>
> Cheers,
>
>         Markus
>
>
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