David R. Karger wrote:
> I agree about depth being a global variable. Thinking about the
> way recursions are usually done, I do think it may be important
> to have an explicit base case, ie a way to have a different lens
> (eg a labellens) take over if you reach maximum depth, rather
> than just silently "giving up" at that point and rendering nothing.
It isn't really a question of giving up. We just say "display down to 5
levels of foaf:knows values". When we reach a depth of 5, we just stop.
The last resource (at depth 5) still gets displayed, but its properties
aren't. This means that we use some kind of label lens for the last
level, but this is implicit (and we do not yet say anything about that
in the documentation; we should).
Are you proposing to add a new Fresnel property that would make it
possible to specify what lens to use to display max depth resources? I
guess we could do that, but I'd keep that for the extended vocab. It
should also be made clear that this last lens cannot use sublens calls.
> From fresnel-dev-return-157-karger=mit.edu_at_simile.mit.edu Mon Jul 11 11:19:06 2005
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> From: Ryan Lee <ryanlee_at_w3.org>
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> To: fresnel-dev_at_simile.mit.edu
> Subject: Re: Manual updated for core vocabulary
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>
> Emmanuel Pietriga wrote:
> > Emmanuel Pietriga wrote:
> >
> >> David R. Karger wrote:
> >>
> >>> What happens if various :sublenses invoke each other with different
> >>> :depth arguments? Is the semantics that depth is a global variable and
> >>> a sublens doesn't apply if the depth exceeds the depth specified for
> >>> that sublens? if so, is there any way to specify a "base case", eg
> >>> what is going to happen if the sublens cannot be invoked because of
> >>> the depth constraint?
> >>
> >>
> >>
> >> I have to think about that. Coming back to it later.
> >
> >
> > Depth should be a global variable. Otherwise we do not prevent infinite
> > recursion.
> >
> > Considering the following lens:
> >
> > :foafPersonDefaultLens rdf:type fresnel:Lens ;
> > fresnel:showProperties (
> > foaf:name
> > [ rdf:type fresnel:PropertyDetails ;
> > fresnel:property foaf:knows ;
> > fresnel:sublens :foafPersonDefaultLens;
> > fresnel:depth "5"^^xsd:nonNegativeInteger ]
> > )
> >
> >
> > the lens shows up to five levels of persons. When it arrives at the 6th
> > recursive call, it just does not show this property. Nothing else
> > happens. We might provide additional Fresnel terms in the extended lens
> > vocabulary to say that in this case the browser should show
> > links/buttons/whatever/... that make it possible to further explore this
> > branch.
> >
> > The same behaviour applies to recursive calls involving more than one
> > lens, knowing that the maximum depth is that declared by the topmost
> > sublens call in the recursion.
> >
> > Ryan, Chris, does this description sound right to you?
>
> Yes, I believe that's how I wrote my code. Although I did realize that
> sublenses with maximum depth less than the current depth+original max
> depth should be honored, so I'll add that in as well.
>
> --
> Ryan Lee ryanlee_at_w3.org
> W3C Research Engineer +1.617.253.5327
> http://simile.mit.edu/
--
Emmanuel Pietriga
INRIA Futurs - Projet In Situ tel : +33 1 69 15 34 66
Bat 490, Université Paris-Sud fax : +33 1 69 15 65 86
91405 ORSAY Cedex FRANCE http://www.lri.fr/~pietriga
Received on Tue Jul 12 2005 - 06:16:41 EDT