[Cube/vo-dml] ivoa datatypes

[CresitelloDittmar, Mark]

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.




> >
> >    2) URL
> >
> >        I would prefer to have a type for URL distinct from anyURI, to
> make the
> > distinction more clear in the models (rather than relying on qualifying
> text).
> >
> What would be the distinction between URL and anyURI?
> At some point the usage of the type is important in deciding the semantic
> meaning of a value (== instance of value-type)
> For example we will likely never have separate types representing age, or
> mass or length. All of these are attributes with datatype ivoa:real or
> ivoa:quantity.RealQuantity. There we leave it up to the definition of the
> attribute to define the semantic meaning of, as well as setting constraints
> on the value.
> What is different in the  difference between URL and anyURI
>

Going back to a reference you sent me a while ago..
  http://www.danielmiessler.com/study/url_vs_uri/

I pull out 2 lines:
  "2) The part that makes a URI a URL is the inclusion of the "access
mechanism", or "network location", e.g. http:// or ftp://."

and
  "For example, you might be told that a file you need is located at
files.hp.com. That's a URI, not a URL--and that system might very well
respond to many protocols over many ports. If you go to
http://files.hp.comyou could conceivably get completely different
content than if you go to
ftp://files.hp.com."

So, I see certain cases, where you want to identify a particular item where
a URL would be appropriate, but not a URI.. to ensure you get the right
thing.
  examples:  DataID.logo , STC.STCBase.href, maybe some documentation
links.

For the majority of cases anyURI would be more appropriate.
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