Re: Meaning of Alt

At 04:12 PM 9/1/00 -0700, Ray Fergerson wrote:
>A question about the semantics of the alternative collection type has
>come up here.  We wanted to construct a model in which a property
>could have a range of, for example, the days of the week.  One
>possibility is to declare a Day_Of_The_Week class with instances
>Monday, etc.  An example of this sort is given in the RDF spec.  In
>our model though we really just need strings and not instances.  We
>don't really want properties to be associated with these things.  We
>initially thought that the Alt was an alternative (hummm) that would
>allow us to just have strings.  A closer reading of the spec seems to
>indicate though that the elements of an alternative collection are
>meant to be equivalent is some way yet different in some other,
>unspecified, way.  Thus you might imagine "Monday", "First workday",
>"Lundi" as the elements of an Alt but not "Monday" and "Tuesday".
>
>Is this interpretation of Alt correct?  Are there other ways to
>specify that the value of a property should be a single value from an
>enumerated set (preferably of strings)?

I tripped over a similar problem recently.  Your posting helped me clarify 
my thoughts.

I think that describing a union data type and listing several alternative 
representations of what is essentially the same value are two very 
different functions that have somehow been conflated with the idea of 
'alternative'.

I think your (latter) interpretation is the only reasonable interpretation 
of rdf:Alt.

I think your former idea needs to be treated as a *schema* issue rather 
than a *representation* issue.  And I think that 'rdf:Alt' is not part of 
the solution.

I suspect that as and when the XML schema data type work is folded into 
RDF, that will provide a way to do what you want.  Per 
http://www.w3.org/DesignIssues/Evolution.html, I think we're operating at a 
level that still depends upon some degree of "Schema option 2".

#g

------------
Graham Klyne
(GK@ACM.ORG)