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Re: "layers" (was Re: the term "named graphs")

From: Dan Brickley <danbri@danbri.org>
Date: Sat, 28 Apr 2012 17:41:58 +0200
Message-ID: <CAFfrAFpxY-7SdPJpEHyS2rXtTz09xcFUaRdo2a3uFEeNCOyxQg@mail.gmail.com>
To: Sandro Hawke <sandro@w3.org>
Cc: RDF-WG Group <public-rdf-wg@w3.org>
[...]

Glad 'layer' appeals to you. I think I picked it up from the mcf spec
originally, http://www.guha.com/mcf/wp.html where it has some more
specific meaning (layers are ordered, and triples are true-or-false
w.r.t. a layer). Or the old Mozilla APIs which also had this. But
Pat's talk of 'surfaces' a few while back was in a similar direction;
triples/claims are written on a surface. Not sure how far we can push
this but the metaphor seems potentially quite developer friendly...

I tried drawing this a few ways, e.g.
http://www.flickr.com/photos/danbri/3472944745/ where each layer there
has a hint as to provenance. Or felt-tip-pen-version,
http://farm4.static.flickr.com/3613/3384528143_8304792836_b.jpg ...

And yes, you're right that it's perhaps a bit weird that URIs are 'on'
multiple layers. Maybe we say (per Pat below) they're "written" on
multiple layers?

files are here,
http://svn.foaf-project.org/foaftown/2009/layers/visuals/layercake2.jpg
with triples and sparql examples nearby,
http://svn.foaf-project.org/foaftown/2009/layers/notes.txt
http://svn.foaf-project.org/foaftown/2009/layers/

e.g. (some goofy uris),

"#According to the layerlist, who made the pages that tell us a
schoolHomepage for Alice?
PREFIX : <http://xmlns.com/foaf/0.1/>
SELECT ?g ?who WHERE {
  GRAPH  <http://localhost/notube/layerlist.rdf> {  ?who :made ?g . }
  GRAPH  ?g {    <http://localhost/notube/layer1.rdf#alice>
:schoolHomepage  <http://lookingglass.example.org/> .  }
}"

For surfaces, see http://www.slideshare.net/PatHayes/rdf-redux ... transcribing:

"""RDF graphs are drawn on surfaces. Blank nodes are marks on the
surface. intuitively, think of a surface as a piece of paper, or a
screen, or a document. .... Surfaces provide the missing type/token
distinction. Putting the same graph onto a new surface is like making
a copy. But copying a graph onto a new surface always gets you new
blank nodes, because a mark can only be on one surface""".

This might be out of date w.r.t. Pat's current thinking but I think
the metaphors are heading in very similar directions.

To pick on the bnode issue, we could imagine operations like copying
from one layer/surface to another, which merits a new bnode. Or maybe
also stitching two layers/surfaces together in a way that preserved
bnodes. (Does modern sparql allow the 'same' bnode in two named
graphs? sorry I forget!)

The only terminology clash I see is with 'layer' from 'layercake'; but
that diagram is fairly internal to the semweb community, and we're
needing terminology that 100s of 1000s of web developers can embrace.

> One cool thing is how much it raises the question, "layer in what?"

Yes, I like that. Not sure how precise we can be; do we consider Web
pages layers, or just somehow things that can be intimately related to
layers?

Dan
Received on Saturday, 28 April 2012 15:42:49 GMT

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