[Cube/vo-dml] ivoa datatypes

[Arnold Rots]

There are three representations of time instants:
(Limited) ISO-8601, JD, MJD
The first is unitless, for the other two 'd' is implied.

In addition, there is a time duration that can be used as a time offset
(i.e., elapsed time since a reference time instant expressed in ISO-8601,
JD, or MJD)
and that can have units s, d, a, yr, cy.

  - 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 Mon, Apr 28, 2014 at 3:23 PM, Rob Seaman <seaman at noao.edu> wrote:

> On Apr 28, 2014, at 12:19 PM, CresitelloDittmar, Mark <
> mdittmar at cfa.harvard.edu> wrote:
>
>
> On Fri, Apr 25, 2014 at 4:55 AM, Gerard Lemson <lemson at mpa-garching.mpg.de
> > wrote:
>
>>
>> > Request:
>> >
>> >   During this effort, there are a couple types that I would like to add
>> to this suite.
>> >
>> >   1) TimeValue: extends AtomicValue
>> >
>> >         + value: datetime     # ivoa:datetime primitive type
>> >         + unit: Unit              # ivoa:unit primitive type.
>> >
>>
>>
>>
> Arnold has made some comments about different types of Time value object
> depending on whether this is absolute or a delta (time since T0).
> Part if my trouble with debating this is not knowing the scope of
> 'datetime'.  Is there an actual specification of what this covers?
> If this is just a time instance type (suitable for DATE keyword), then it
> may not be what is desired under Quantity.
>
>
> Perhaps start with use cases.  “Time” is arguably the broadest topic in
> existence.  Before a specification, one needs engineering requirements.
>  Before requirements, a concept of operations.  What is it you (the
> collective “you”) are trying to represent and for what purpose?
>
> Rob
>
>
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