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collection vs dataset EOD? Re: orthogonality (was Re: New attempt)

Hi John and Joe,

Since I was asked, I am answering, not that I am adding anything useful.

Yes, if collections and datasets are completely interchangable in all
machine-type ways, that works for me.   I think John gives the definitive
summary below.  Of course, if I have a dataset that temporarily does not have
any functioning access methods on a particular server, one may not always feel
the need to relabel it a collection...


Quoting John Caron and Joe <address@hidden>:

> > If this is the case then I would suggest that
> >
> > a) this distinction be preserved by allowing both tags to be
> > used(possibly renamed if it would clarify things); and
> >
> > b) data providers should be encouraged to mark up their catalogs
> > appropriately using the two tags, so that THREDDS client UI's can take
> > advantage of this to present catalogs in an intuitive way; but
> >
> > c) these tags should be completely interchangeable in all other ways
> > (i.e. same type in the DTD/Schema, and same API calls, any tag that can
> > go in a dataset can also go in a collection), since they are
> > semantically equivalent at a machine level.
> >
> > Does that make any sense? Benno, would that satisfy you?
> >
> > - Joe (ready for a checkup with my ontologist)

Quoting John: 

> Actually Im inclined to take it a bit further.
> Currently a collection is just some collection of datasets that share some
> common theme. If we allow it also to be a dataset (meaning it has a URL,
> can
> be selected, etc) then I think it should have the meaning that contained
> datasets are subsets or specializations of it. Because if they are not it
> seems to me that you might as well just represent the collection-as-dataset
> as a contained dataset element. [Maybe in this whole discussion I have been
> trying to convince myself of that :^] Does everyone agree with that meaning
> of nested datasets inside of collection-as-dataset?
> PS: There are still semantic difference between collections and datasets: A
> dataset has one or more access elements, a collection 0 or more.
> Collections
> contain datasets and nested collections.
> OTOH, datasets and collections look so similar already in the XML, its
> tempting to combine them (which i was playing with earlier in
> http://www.unidata.ucar.edu/projects/THREDDS/xml/InvCatalog.0.6a.dtd)

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