[Mulgara-dev] Exception for missing graphs in mulgara.

[Amit Kapoor]

Hi Paul,

On Thu, Jan 08, 2009 at 01:56:55PM +1100, Paul Gearon wrote:
[snip]
> I don't think it's appropriate to only say that the graph doesn't
> exist, since there are cases when the appropriate error would be to
> say that the protocol is unknown.  (e.g. You forgot to load the http
> resolver and asked for a graph from http). I think it's more correct
> (though maybe less user-friendly) to say something like:
>   "Graph <local://mydata> not found locally, and protocol "local" not supported"
> Supported protocols would then have a different error:
>   "Graph <http://somehost/mydata.rdf> not found."
> This would indicate that the URI was not stored locally, and the
> registered protocol handler couldn't get it either. That would need a
> bit of interaction with the protocol-registered resolvers, but I think
> the extra work there is important.
> 
> Would that be suitable?

    So the basic lookup that is failing is the resolver for the graph URI? And
    that is done either via the complete URI or just the scheme in the URI...

    Does it really matter in that case whether the lookup is failing because of
    it being un-registered in system graph or un-registered scheme from an
    end-user perspective? Wouldn't they be able to figure out what the
    registration scheme they want if they are notified that the 'Could not
    locate resolver for graph <uri>. Missing in both system graph and/or scheme
    map.' or something like that?

    regards