[SensorML] SweCommon: Time

Alexandre Robin robin at nsstc.uah.edu
Fri Jun 22 11:00:01 EDT 2007


Hi Johannes,

The reason why all these different choices are still in there is to be able
to support a maximum of cases.

(1) xs:time and xs:date would be used in the case where date and time of day
are given in two separate fields of a dataset. xs:dateTime only works if
both are given in the same field... I know that's not exactly the meaning
intended by W3C XMLSchema for xs:date and xs:time but what else can we do?
Create our own type?

(2) xs:double is needed to specify a delay after an epoch specified by the
referenceFrame or referenceTime (itself an ISO8601 dateTime).

(3) Any type of time interval should be supported by TimeRange right now. We
haven't added support for ISO duration notation (ex. P1D) because we feel it
is just as easy to use a Quantity with the appropriate unit... We may want
to add support for that later...

The ultimate thing that would tell you what the time really represent is the
definition attribute anyway, just like any other simpleType we use in SWE
Common... 

Of course if that seems really too hard to support in a client, we can
discuss and limit the possibilities. For instance (1) may not really be
needed since it MAY always be possible to reformat a dataset and merge date
and time in the same field... But right now I am reluctant to enforce
that...

Cheers,

--------------------------------------------
Alexandre Robin
Research Scientist
National Space Science and Technology Center
(256) 961 7978



> -----Original Message-----
> From: sensorml-bounces+robin=nsstc.uah.edu at opengeospatial.org
> [mailto:sensorml-bounces+robin=nsstc.uah.edu at opengeospatial.org] On Behalf
> Of Johannes Echterhoff
> Sent: Thursday, June 21, 2007 9:27 AM
> To: sensorml at opengeospatial.org
> Subject: [SensorML] SweCommon: Time
> 
> Hi.
> 
> I have a question concerning the possible meanings of swe:Time. Such an
> element can have four different representations: a string (before,
> after, now or unknown from gml:TimeIndeterminateValueType), a double,
> xs:data, xs:time or xs:dateTime.
> 
> The meaning of each of the possible representations is quite different:
> 
>     * gml:TimeIndeterminateValueType does not provide a specific time
>       instance but rather an indeterminate value (as the name says)
>     * The double value would always have to be computed with respect to
>       the given referenceFrame. This could result in a time instance but
>       could also be a duration or recurring time depending on the
>       reference frame, or am I missing something?
>     * xs:date defines a duration (one-day long) at a specific date (e.g.
>       2007-06-07).
>     * xs:time represents an instant of time that recurs every day.
>     * xs:dateTime finally represents a specific instance of time.
> 
> My question is: was it intended to allow all of these different meanings
> for the swe:Time element? I thought that swe:Time would represent an
> instance of time in the end, but now I am no longer sure about that.
> 
> Best regards,
>     Johannes
> 
> --
> Johannes Echterhoff
> Institute for Geoinformatics (IfGI), University of Muenster, Germany
> Robert-Koch-Str. 26-28, D - 48149 Muenster
> 
> Fon: +49 (0)251 83 39761
> Fax: +49 (0)251 83 39763
> 
> IfGI-site: http://ifgi.uni-muenster.de/
> 
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