Re: Considerations on RDF presentation

From: Chris Bizer <>
Date: Sun, 20 Mar 2005 18:49:08 -0500

Hi Stefano,

interesting new ideas.

> I believe the biggest mistake we made was to consider the output of a
> lens an RDF model (a tree encoded in a graph with explicit names of
> relationships) instead of thinking of it as an XML model (a tree encoded
> in a tree-oriented structure with implicit nesting relationships). This
> creates unnecessary complexity to the 'style' part of fresnel and for no
> benefit.

You might be right about the mistake. I'm not sure yet.

We definitively don't want implizit relationsships because such a
transformation would be a information loss.

So basically we are talking about styling a tree like this:

       rdf:type foaf:Person
       foaf:name "Stefano"
       foaf:knows ex:ryan
                          rdf:type foaf:Person
                          foaf:name "Stefano"

Or a little bit more verbose if expressed in XML, on which we could use CSS

Questions questions coming to my mind with this approach are:

1. Is CSS alone expressive enought?
We are having this PropertyValueStyle vocabulary in Fresnel for saying that
values of foaf:depict should be retrieved and rendered as an image, video or
whatever. How could we express this with CSS?
Would we extend CSS?

2. Is the CSS selector language expressive enought?
Currently we can say stuff like "Display be labels of all properties in a
certain namespace bold" or "Draw a gray frame around all persons that are
older than 70 years". I guess it would be hard to express this in the CSS
selector language?

3. What about labels?
In order to have proper property labels we would have to mode the labeling
vocabulary from the styling to the selection part of fresnel, which feels
wrong: Labels are definitivly style.

Let me try to sketch an XML tree including property labels, in order to see
if we can style it with CSS.

<foaf:person uri=ex:stefano>
        <foaf:name fresnel:label="Name: ">Stefano</foaf:name>
        <foaf:homepage fresnel:label="Person's Homepage:
        <foaf:homepage fresnel:label="Person's Homepage:

and than have CSS styles like

foaf:person {border-top-style: solid }

OK. I guess this would work in general. But we are blurring the destinction
between styling and selection with custom labels like "Person's Homepage: ".
Might not matter.

Also the CSS selectors are getting tricky.

Can I say in CSS that the second "Person's Homepage:" shouldn't be
How do I get the comma between the two homepages and the dot at the end?

> But I do advocate that we should aim at a clearer separation between
> Fresnel and CSS, allowing lenses to be 'classified' and CSS selectors to
> work on those lenses, instead of using fresnel selectors for selection
> and embedding CSS instructions in the fresnel model directly as we do

I don't get what you mean with classified. Why can't we just use the names
given by the RDF schema as shown above and attach the CSS style to them?

It is an interesting think piece if we should go down the XML path or not.
Gives us an interesting topic for our meting tomorrow.


P.S. The first part of your mail is also great input for the paper about
fresnel ;-)
Received on Sun Mar 20 2005 - 23:47:48 EST

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