Re: AW: FSL and subclass/subproperty relationships

From: Emmanuel Pietriga <>
Date: Wed, 02 Nov 2005 08:39:53 +0100

David Karger wrote:
> "Exposing" subtyping to the user to decide whether to use it or not
> seems strange to me. Also good source of bugs when people try to use
> other lenses recursively.

It all depends who you call a "user". I was not intending to expose
"end-users" to subtyping relationships (by end-user I mean here people
who do not necessarily have knowledge about SemWeb or any
programming-related skills). Only people who write Fresnel code should
see FSL expressions (as only XSLT programmers see XPath expressions, not
"end-users" who browse XSLT-generated HTML pages).

> How about we instead maintain the standard
> semantic web perspective that inference is desirable but never
> guaranteed---namely, when someone writes into fresnel that the lens
> applies to a type, the proper inference is that it also applies to
> subtypes, but since inference is never guaranteed to work, there may be
> some implementations that will fail to "notice" that a given subtype
> relationship applies.

I am not sure I understand your position. Are you questioning the whole
idea of allowing Fresnel programmers to explicitly say whether a type
test matches subclasses/subproperties or not? Or are you just
questioning which behavior should be the default?

> Emmanuel Pietriga wrote:
>> Emmanuel Pietriga wrote:
>>> Ryan Lee wrote:
>>> > Chris Bizer wrote:
>>> >
>>> >> Hi Emmanuel,
>>> >>
>>> >> I think this is definitively useful behaviour. The question which is
>>> >> coming
>>> >> to my mind is, what should be the default behaviour?
>>> >>
>>> >> Should the query engine by default use subproperty and subclass
>>> >> relationships, which I guess will slow it significantly down?
>>> It will slow it down, but I'm not sure to what extent (this will
>>> partially depend on the complexity of class and property hierarchies).
>>> But I would say that the language's expressive power and ease of use is
>>> more important than implementation/performance issues (though these of
>>> course have to be taken into account).
>>> >> My understanding is that Fresnel is about visualizing
>>> materialized RDF
>>> >> graphs and inferencing (if needed) is done on a lower layer before
>>> >> Fresnel
>>> >> gets involved.
>>> Yes indeed. But if you think about the Fresnel presentation designer, it
>>> can be very convenient to write a single lens that will apply to a class
>>> and all its subclasses. If you don't have subclass/subproperty
>>> inferencing at the FSL level, you have to define as many lens domains as
>>> there are subclasses. And the lens won't apply to subclasses that the
>>> stylesheet designer did not know of (or forgot).
>>> > This is the same approach SPARQL is also taking.
>>> >>
>>> >> Thus I think (if at all) you should tell the engine explicitly to do
>>> >> inferencing using '!' and the none-inferencing case should be the
>>> >> default.
>>> >
>>> >
>>> > Agreed.
>>> Ok, so we all seem to agree that this is a useful feature. We only
>>> disagree on whether this should be the default behaviour and on the
>>> syntax.
>>> I'm okay witht the idea of having the subclass/subproperty-unaware
>>> version the default, but then I'm not sure I like "!" as the notation
>>> for the subclass/subproperty-aware version. I can live with it, that's
>>> mostly a question of personal taste, but if anybody has another idea for
>>> how to convey this, please submit it. Unless everybody's happy with the
>>> ! notation, in which case we'll leave it as such.
>> Coming back to this issue after a while, here's what I am about to do:
>> - default type tests will be subclass/subproperty-unaware
>> - symbol ^ will be used as a type test prefix to denote a
>> subclass/subproperty-aware type test.
>> So:
>> */ex:prop1/*
>> would only select paths that go through ex:prop1 properties, but not
>> subproperties of ex:prop1,
>> while:
>> */^ex:prop1/*
>> would select paths that go through ex:prop1 properties or
>> subproperties of it.

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
Received on Wed Nov 02 2005 - 07:34:43 EST

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