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Re: (proposal) was Re: defn of Named Graph

From: Sandro Hawke <sandro@w3.org>
Date: Thu, 26 Sep 2013 13:32:28 -0400
Message-ID: <52446FAC.2020907@w3.org>
To: Peter Patel-Schneider <pfpschneider@gmail.com>
CC: Guus Schreiber <guus.schreiber@vu.nl>, Dan Brickley <danbri@danbri.org>, Pat Hayes <phayes@ihmc.us>, Jeremy J Carroll <jjc@syapse.com>, RDF WG <public-rdf-wg@w3.org>
On 09/26/2013 12:00 PM, Peter Patel-Schneider wrote:
> Umm,  doesn't a lot of this have normative consequences? If not, then 
> is there any reason to have it?  If so, then both Concepts and 
> Semantics will have to have changes to support it, and there has to be 
> a design that the WG can vote on before proceeding.

There's a conceptual part (that doesn't affect running code) and an 
optional part that would just be in a WG Note.

The conceptual part is (1) telling people what a "Named Graph" is, and 
maybe (2) shifting the terminology around "RDF Graph".    My sense is 
this would clear up a lot of confusion, but perhaps I'm just arguing 
about angels on the head of a pin and this would cause more confusion.  
I have no interest in pushing this if people are okay with the status 
quo.   We claim RDF Graphs are mathematical sets, but that doesn't seem 
to be how the real world works with them.   Does that matter?    *shrug*

The optional part is one RDF class, with a standard name (eg 
rdf:NGDataset), which would allow people to indicate in a dataset that 
it has certain semantics (that seem obvious to me, and I think most 
people use without it being formally specified).   I also have no 
interest in pushing this, if no one needs that kind of interoperability.

If the WG passes on both of these, they can be handled later, except 
that it'll be harder to shift the terminology.

        -- Sandro

> peter
> On Thu, Sep 26, 2013 at 5:11 AM, Sandro Hawke <sandro@w3.org 
> <mailto:sandro@w3.org>> wrote:
>     On 09/25/2013 12:11 PM, Guus Schreiber wrote:
>         Sandro, Jeremy, Pat, Dan, Gregg, (cc: RDF WG)
>         Thanks for having this constructive discussion.  Given the
>         timeline of the RDF WG we really need to formulate a WG
>         response to the issue [1] raised by Jeremy *by 2 October*.  It
>         would be great if we can do this in the custom consensual way.
>         Any chance we can achieve this over the next 7 days?
>         Thanks in advance!
>     I'm replying to the WG now, because thinking about this some more,
>     I'm still very happy with the proposal quoted below, and I'd like
>     the WG to support it.
>     To summarize and clarify, I propose:
>     1.  We define the term "Named Graph" informally to be like an "RDF
>     Graph" but with its own identity, distinct from the triples it
>     happens to contain.
>     2. We briefly apologize for the confusing names -- a Named Graph
>     is not actually an RDF Graph that happens to have been given a
>     name -- it's a fundamentally different thing that *can* be given a
>     name. (It's what Pat likes to call a surface and I like to call a
>     g-box.)   When people say "graph" in the RDF world, they are often
>     talking about Named Graphs, not RDF Graphs, as evidenced by them
>     talking about "putting things into the graph", or otherwise
>     changing them.  Such concepts are nonsensical with RDF Graphs.
>      (If we had more time, I'd suggest we renamed "RDF Graph" to
>     "Abstract Graph", but I suppose it's too late for that.  Maybe we
>     can use the word "abstract" editorially a few places....)
>     3. We note that RDF Datasets can be used to state which triples
>     are in certain Named Graphs.
>     4. We define a class (eg rdf:BasicDataset) of the Datasets which
>     have those semantics.
>     Strawpoll: If I wrote this up for a WG note, in a style you liked,
>     would you support the WG publishing it?
>     Do you think we can also put (1) into RDF Concepts?   It has no
>     normative consequences, so it's plausible to do it after Last
>     Call, although we shouldn't do it if the community is going to
>     hate it.
>           -- Sandro
>         Best,
>         Guus
>         [1] http://www.w3.org/2011/rdf-wg/track/issues/142
>         For RDF WG members: see thread starting with:
>         http://lists.w3.org/Archives/Public/www-archive/2013Sep/0025.html:
>         Following that epiphany I had at the end of my last email,
>         here's what
>         I'd love to see everyone agree on, more or less:
>         == Named Graphs
>         An "RDF Named Graph" is similar to an "RDF Graph", but
>         different in one
>         important way.    Because RDF Graphs are defined as being
>         mathematical
>         sets of RDF Triples, any two RDF Graphs which happen to
>         contain the same
>         RDF Triples are, by definition, the same thing. This means that
>         statements made about any RDF Graph, such as metadata about
>         provenance
>         and licenses, necessarily apply wherever the same set of RDF
>         Triples
>         occurs.   This is not always the desired intent, and Named Graphs
>         provide an alternative.
>         Like an RDF Graph, an RDF Named Graph contains zero or more RDF
>         Triples.  Unlike an RDF Graph, an RDF Named Graph has an identity
>         distinct from those triples.  That is, two Named Graphs remain
>         distinct
>         and distinguishable entities even if they happen to contain
>         exactly the
>         same RDF Triples.
>         The term "Named Graph" has historically caused some confusion,
>         as some
>         people have read the phrase to mean "an RDF Graph which
>         happens to have
>         a name".   This reading is not correct, since RDF Named Graphs
>         are not
>         RDF Graphs at all.   They might reasonably have been called
>         "Identifiable Graphs", which contrasts them to "RDF Graphs" in
>         the same
>         way that a counterfeit dollar bill is not technically a dollar
>         bill.
>         As in the dollar bill analogy, RDF Named Graphs and RDF Graphs
>         have a
>         lot in common, but in some circumstances it is critical to
>         distinguish
>         between them.    Other names that have been suggested for
>         Named Graphs
>         include "surfaces" and "g-boxes", but "named graph" has been
>         cemented by
>         its use in the SPARQL syntax.
>         Names Graphs also provide a useful semantics for RDF Datasets.
>         Some RDF
>         Datasets, hereafter NG Datasets, have this intended meaning: each
>         (_name_, _graph_) pair is a statement that _name_ is a Named
>         Graph which
>         contains exactly the triples in _graph_.    The class
>         rdf:NGDataset is
>         defined for signalling these are the intended Dataset semantics.
>         The class rdf:NamedGraph is defined for use in declaring the
>         domain and
>         range of predicates which relate Named Graphs.   For example:
>            <> a rdf:NGDataset
>            GRAPH :g1 { :MtEverest :heightFeet 29002 }
>            GRAPH :g2 { :MtEverest :heightFeet 29029 }
>            :g1 :claimedBy :BritishIndiaSurveyOffice.
>            :g2 :claimedBy :IndiaSurveyOffice.
>         Here, the domain of :claimedBy is rdf:NamedGraph, and it might be
>         defined in English as "x :claimedBy y means that all the
>         triples in the
>         Named Graph x are claimed to be true by the social entity y."
>         The greatest differences between RDF Graphs and RDF Named
>         Graphs appear
>         when one considers the possibility of them changing over time.
>         It is
>         nonsensical to consider an RDF Graph changing over time, just
>         like it
>         makes no sense to talk about the value of some integer, say seven,
>         changing over time.   In contrast, it makes perfect sense to
>         consider
>         Named Graphs changing: at one point in time the identifiable
>         thing that
>         is a certain Named Graph contains some triples and at another
>         point in
>         time it might contain different triples.  As of RDF 1.1,
>         however, the
>         formal specifications for RDF do not provide any specific
>         support for
>         handling changing data.
>         ==
>         That's simple and clear enough, isn't it?     ( ... he says,
>         clinging to
>         perhaps his last shred of hope. )
>                 -- Sandro
Received on Thursday, 26 September 2013 17:32:40 UTC

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