Caveat !!! Re: Special attention To Alberto Re: SODA erratum 3 proposal

[BONNAREL FRANCOIS]

  A sentence had been suppressed in my previous email. Sorry about this !
Le 15/02/2023 à 18:30, BONNAREL FRANCOIS a écrit :
> 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
>
"For float-valued intervals (e.g., the standard BAND and TIME 
parameters), only aMAXis given. It contains two floating-point values,  
separated by a blank. These correspond to the bounds of the daraset on 
the corresponding axis. Example"
>
> 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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