ivoa: DM type system

[Arnold Rots]

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



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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 11:07 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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