Special attention To Alberto Re: SODA erratum 3 proposal

[BONNAREL FRANCOIS]

Le 14/02/2023 à 18:48, Mark Taylor a écrit :
> Alberto,
>
> On Tue, 14 Feb 2023, alberto micol wrote:
>
>> Before answering Francois’ request for my comments,
>> I need to ask a question to Mark.
> I'm assuming you're asking me with my taplint/votlint hat on.
>   
>> I do agree with you, Mark, that using scalar MIN and MAX values
>> for a xtype=“interval" element is the least surprising semantics,
>> but...
>>
>> Votable 1.4 seems to require that the MIN and MAX <VALUES> must be of the same arraysize as the parent parameter.
> Is that true?  I may be missing it but I don't see text in VOTable 1.4
> that says that.  I don't see anything much in the text that mandates
> what has to go into the MIN/MAX value attribute, beyond a couple of
> examples.  It's sort of obvious for scalar numeric fields,
> but far from obvious for array values.  For that reason
> (as far as I can remember) votlint/taplint does not attempt to
> validate the MIN/MAX values - currently, you can write anything
> in there and votlint/taplint will not tell you off.
>
> If future versions of the VOTable standard are clearer about what
> can go into MIN and MAX, I expect I will update the validator logic
> to report non-compliance.
>
>> Indeed ASTROPY complains if the arraysizes of the VALUES MIN and MAX are not the same as for the PARAM:
>> WARNING: E02: ?:?:?: E02: Incorrect number of elements in array. Expected multiple of 2, got 1 [astropy.io.votable.converters]
> So it looks like the astropy validator made a different decision about
> how to validate those elements than I did.
>
>> I understand VOTable 1.5 is supposed to change this; the new text reads:
>>> When the parent of a VALUES element does have an xtype, special rules apply;
>>> clients should only try to parse limits of xtyped fields when they know the xtype.
>> The text “when they know the xtype” confuses me quite a bit. What does that mean in practice? For example:
>> How will a validator understand how to validate a votable with MIN/MAX VALUES expressed with arraysizes different than its parent element,
>> as suggested for the MIN MAX of an interval ?
> I think the idea is that where a known xtype is present, parsers
> (and validators) should interpret the MIN/MAX in accordance with
> special rules about MIN/MAX that are provided along with the
> xtype definition (most likely in DALI); those rules will explain
> what the constraints are for that xtype.  If an unrecognised xtype
> is present, parsers can't make sense of MIN/MAX and shouldn't try.
> In absence of xtype, MIN/MAX has to be a scalar with "obvious"
> semantics.

If we choose the scalar generic solution then the following text in 4.2

"For float-valued intervals (e.g., the standard BAND and TIME 
parameters),VALUES/MINandVALUES/MAXshould be used to communicate the 
range of values for which clients can expect to receive data"

should become

For float-valued intervals (e.g., the standard BAND and TIME 
parameters),VALUES/MINandVALUES/MAXshould be used to communicate the 
range of values for which clients can expect to receive data as stated 
for MIN/MAX values in the generic case starting from VOTable 1.5"


But in the same 4.2 subsection we give examples for CIRCLE and POLYGON 
parameters and say

1 ) "For CIRCLE, only a MAX is given. It contains three floating point 
values, separated by whitespace. These correspond to the RA and Dec of 
the center of a spherical circle covering the dataset, and a radius of 
such a covering circle. "

Which look like a definition of how we could  interpret MIN/MAX in the 
case of xtype="circle" in DALI-next

  2 ) "For POLYGON, again only aMAXis given. It consists of a sequence 
of floating-point values, again separated by blanks, describing RA and 
Dec of the vertices of a spherical polygon covering the dataset. Data 
providers are encouraged to choose a minimal polygon. Example:"

Which look like a definition of how we could  interpret MIN/MAX in the 
case of xtype="polygon" in DALI-next

So for consistency in this subsection we could also write

We could also add in parenthesis (xtype="interval, xtype="circle", 
xtype="polygon") at the right place in the text

Thoughts ?

Cheers

François

>
>> One could even write:
>> <PARAM arraysize=“2” xtype=“interval” name=“BAND”…>
>> <VALUES>
>>   <MIN arraysize=“” …>
>>   <MAX arraysize=“55” …>
>> </VALUES>
>> </PARAM>
>> Votable 1.5 seems to allow such possibility !
> No, since (a) where the interval xtype is defined there should be
> rules about how to use MIN/MAX and (b) there is no arraysize
> attribute defined on the MIN/MAX elements.
>
>> In which case the validator will need to simply omit any check on those MIN MAX values, right?
>> That does not seem particularly healthy.
> About what one can not speak, one must remain silent.
>
> Mark
>
> --
> Mark Taylor  Astronomical Programmer  Physics, Bristol University, UK
> m.b.taylor at bristol.ac.uk           http://www.star.bristol.ac.uk/~mbt/

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