ivoa: DM type system

[Arnold Rots]

Oh, and proleptic Gregorian. See section 3 of the WCS paper.

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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 Tue, Apr 18, 2017 at 11:27 AM, Arnold Rots <arots at cfa.harvard.edu> wrote:

> The datetime string (subset of ISO-8601, as defined in FITS WCS paper VI)
> is specified as:
>
> [+|-C]CCYY-MM-DD[Thh:mm:ss[.s...]]
>
> 'T' is a literal, the other letters stand for single digits with obvious
> meaning.
>
>   - Arnold
>
>
>
> ------------------------------------------------------------
> -------------------------------------------------
> Arnold H. Rots                                          Chandra X-ray
> Science Center
> Smithsonian Astrophysical Observatory                   tel:  +1 617 496
> 7701 <(617)%20496-7701>
> 60 Garden Street, MS 67                                      fax:  +1 617
> 495 7356 <(617)%20495-7356>
> Cambridge, MA 02138
> arots at cfa.harvard.edu
> USA
> http://hea-www.harvard.edu/~arots/
> ------------------------------------------------------------
> --------------------------------------------------
>
>
> On Tue, Apr 18, 2017 at 11:07 AM, Gerard Lemson <gerard.lemson at gmail.com>
> wrote:
>
>> Hi Mark
>>
>> On Mon, Apr 17, 2017 at 11:51 AM, CresitelloDittmar, Mark <
>> mdittmar at cfa.harvard.edu> wrote:
>>
>>>
>>>
>>> ...
>>>>
>>> I don't think this needs to be complicated, so let's put these on the
>>> back burner.
>>>
>>> Thanks!
>>
>>>
>>> >>     * Quantity and datetime would not have a common ancestor, so we
>>> could not define a TimeStamp
>>> >>       which would allow time represented as a RealQuantity OR
>>> datetime.
>>> >>       https://volute.g-vo.org/svn/trunk/projects/dm/STC-
>>> <https://volute.g-vo.org/svn/trunk/projects/dm/STC-2.0/doc/diagrams/alt/temporal%20domain%20diagram.png>
>>> 2.0/doc/diagrams/alt/temporal%20domain%20diagram.png
>>> <https://volute.g-vo.org/svn/trunk/projects/dm/STC-2.0/doc/diagrams/alt/temporal%20domain%20diagram.png>
>>> >>
>>>
>>> >So are you saying you'd like a DatetimeQuantity? With only a "datetime
>>> unit" being sufficient?
>>> >I had hoped   'ivoa:datetime' would be sufficient and the precise
>>> representation would be left to the mapping.
>>>
>>> This sounds like you are suggesting that 'ivoa:datetime' should suffice
>>> for all uses.
>>>    MJDREF  = 50814.02               / [d] zero point for times - MJD
>>>    TSTART  = 84244214.7546979934 <(754)%20697-9934>    / [s]
>>> Observation start time
>>>    DATE-OBS= "2000-09-02T01:10:14"  / Date and time of observation start
>>>
>>> I want all of these to be a TimeStamp type (abstract).
>>>   * datetime = has vodml/html description:  "Represents a moment in time
>>> using a date+timestamp."
>>> which covers 'DATE-OBS', the other 2 are satisfied by RealQuantity.
>>>
>>> But.. since RealQuantity and datetime do not have a common ancestor, I
>>> cannot define TimeStamp without either an anyType or a DateQuantity.
>>>
>>>
>> Yes, that is correct, but I see now (I think) what might cause confusion,
>> namely the description of  ivoa:datetime in the model as
>> "Represents a moment in time using a date+timestamp". What was meant
>> there is that it is not just a day/date (2017-04-18), and not just a time
>> ("13:00:01.3"), but the fully specified moment in time.
>> In the current description it does indeed sound as if date and time must
>> be represented, i.e. too much like a prescription for valid serializations.
>> This was NOT intended.
>> ivoa:datetime is supposed to represent the concept of a Timestamp as you
>> mention it, and it should be up to serialization prescriptions to take care
>> of valid representations.
>>
>> So if that interpretation is given to ivoa:datetime, would that type be
>> sufficient for your requirements?
>>
>> Cheers
>> Gerard
>>
>>
>>
>>
>>> Mark
>>>
>>>
>>>
>>
>
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