Re: Manual updated for core vocabulary

From: David R. Karger <>
Date: Mon, 11 Jul 2005 11:22:34 -0400

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.
        From Mon Jul 11 11:19:06 2005
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        Date: Mon, 11 Jul 2005 11:18:33 -0400
        From: Ryan Lee <>
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        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
        W3C Research Engineer +1.617.253.5327
Received on Mon Jul 11 2005 - 15:19:47 EDT

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