ivoa: DM type system
Arnold Rots
arots at cfa.harvard.edu
Tue Apr 18 18:07:37 CEST 2017
A time stamp is a specification on a particular time instance instance
within a given space-time frame
This can be represented as a Julian Date or Modified Julian Date (in which
case its primitive is a real) or as a datetime primitive which is to be
implemented as a calendar-based string.
-------------------------------------------------------------------------------------------------------------
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/
--------------------------------------------------------------------------------------------------------------
On Tue, Apr 18, 2017 at 11:53 AM, Gerard Lemson <gerard.lemson at gmail.com>
wrote:
> Hi Arnold
>
>
>
>
>
> On Tue, Apr 18, 2017 at 11:33 AM, Arnold Rots <arots at cfa.harvard.edu>
> wrote:
>
>> Oh, and proleptic Gregorian. See section 3 of the WCS paper.
>>
>> ------------------------------------------------------------
>> -------------------------------------------------
>> 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 11:27 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
>>>
>>>
>>>
>>>
> This still seems to be a definition in terms of a serialization that in
> the VO-DML base types I would like to avoid.
> Just like we do not want to be bothered by how an ivoa:real is represented
> (ASCII-decimal, IEEE standard floating point, whatever).
>
> I don't know what the best description of this serialization-independent
> concept would be.
> Would something like "the 0 component of some observer's four vector
> identifying an event in 4-d space-time" be correct?
>
> Cheers
> Gerard
>
>
>
>> ------------------------------------------------------------
>>> -------------------------------------------------
>>> 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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