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Re: Why do we name nodes and not edges?

From: Hugh Glaser <hg@ecs.soton.ac.uk>
Date: Sun, 29 Jul 2012 12:17:29 +0000
To: Natasa Bulatovic <bulatovic@MPDL.MPG.DE>
CC: "semantic-web@w3.org" <semantic-web@w3.org>, Steve Harris <steve.harris@garlik.com>
Message-ID: <064B2244-D783-4F0E-B850-DA05D0C1E504@soton.ac.uk>
I don't think that Steve was suggesting it might ever be useful or recommended - just possible. :-)

Let's see.

The simplest thing I can come up with (thanks Mike Uschold) is:
id:john id:john_married_jane id:jane .
id:john_married_jane id:in_place id:london .
and you could then do:
SELECT ?where WHERE { ?s id:john_married_jane ?w . id:john_married_jane id:in_place ?where }
you would probably benefit from
id:john_married_jane rdfs:subPropertyOf id:married .

I dumped some stuff in a store, if you want to try:
http://test.rkbexplorer.com/sparql/
And of course as Linked Data: http://test.rkbexplorer.com/id/john_married_jane
RDF is here: http://test.rkbexplorer.com/models/me.ttl
The above query is
(http://test.rkbexplorer.com/sparql/?format=browse&query=PREFIX+id%3A+++%3Chttp%3A%2F%2Ftest.rkbexplorer.com%2Fid%2F%3E%0D%0ASELECT+%3Fwhere+WHERE+%7B+%3Fs+id%3Ajohn_married_jane+%3Fw+.+id%3Ajohn_married_jane+id%3Ain_place+%3Fwhere+%7D%0D%0A)

I also have some labels (everything should always have labels, even/especially properties), so you can do:
SELECT ?event_label ?where_label WHERE
{ ?s id:john_married_jane ?w . id:john_married_jane id:in_place ?where . id:john_married_jane rdfs:label ?event_label . ?where rdfs:label ?where_label .}

As I say, I am not sure how useful it is.
In fact for this sort of thing I prefer to move to a proper event-based model, as CIDOC/CRM does.
But it is all perfectly valid, and looking back at it, it seems a perfectly sensible way of doing it.
So it must be one of the patterns that modelling people recommend? ;-)
I could have complicated it with bnodes or classes, but I think this makes it quite readable.
A little amusement on a sunny Sunday afternoon - better than having to do the gardening.
Back to the Olympics and the GrandPrix - life is so tiring.

Cheers
On 25 Jul 2012, at 17:11, Natasa Bulatovic <bulatovic@MPDL.MPG.DE> wrote:

> Could you point to some examples where this scenario would be useful or recommended?
> 
> Cheers,
> Natasa
> 
> Am 25.07.2012 18:04, schrieb Dave Reynolds:
>> If I understand Steve's point he was meaning that you can mint a new unique edge:xxxxxx identifier for each edge.
>> 
>> [Presumably you could make that a subPropertyOf the actual property you wanted to assert.]
>> 
>> Cheers,
>> Dave
>> 
>> On 25/07/12 16:47, Aidan Hogan wrote:
>>> Steve,
>>> 
>>> If I understand Melvin's point, in RDF, edge:123456 is the URI of a
>>> property used to label the edge, not the edge itself.
>>> 
>>> Analogously, you don't identify a class-instance by it's class URI.
>>> 
>>> An edge is between two things. It might be directed and it might be
>>> labelled. In RDF it's both.
>>> 
>>> Hence, the edge would encapsulate the full triple, including source
>>> (subject) and target (object) nodes, as well as the label (predicate).
>>> 
>>> Cheers,
>>> Aidan
>>> 
>>> On 25/07/2012 16:18, Steve Harris wrote:
>>>> Nothing stops you from giving edges a unique URI, infact I think I've
>>>> worked on systems that did that.
>>>> 
>>>> e.g.
>>>> 
>>>> <foo> <http://example.com/edge/123456> 1 .
>>>> <http://example.com/edge/123456> a rdf:Property .
>>>> ...
>>>> 
>>>> - Steve
>>>> 
>>>> On 2012-07-25, at 16:07, Melvin Carvalho wrote:
>>>> 
>>>>> Sorry if this topic has been covered before, but I have a question
>>>>> based on the axioms of the web, in particular:
>>>>> 
>>>>> *Axiom 0a: Universality 2    Any resource of significance should be
>>>>> given a URI.
>>>>> *
>>>>> In this case we consider the web to be a directed graph (of nodes and
>>>>> edges), where a *node* corresponds to a *resource* but edge does not.
>>>>> 
>>>>> We are encouraged to make nodes universal by giving them a URI.
>>>>> 
>>>>> Why dont edges get the same treatment, ie encouragment to give it a
>>>>> (universal) name.  Is it even practical?
>>>>> 
>>>>> I know there's such thing as reification but that seems to be
>>>>> unpopular (maybe before my time).
>>>>> 
>>>>> I'm just curious as to whether this seems asymmetrical, that nodes are
>>>>> seemigly treated in one way, and edges in another?
>>>> 
>>>> -- 
>>>> Steve Harris, CTO
>>>> Garlik, a part of Experian
>>>> +44 7854 417 874 http://www.garlik.com/
>>>> Registered in England and Wales 653331 VAT # 887 1335 93
>>>> Registered office: Landmark House, Experian Way, Nottingham, Notts,
>>>> NG80 1ZZ
>>>> 
>>> 
>>> 
>> 
>> 
> 
> -- 
> --
> Natasa Bulatovic
> Max Planck Digital Library (MPDL)
> Amalienstrasse 33
> 80799 Munich, Germany
> http://www.mpdl.mpg.de
> 
> e-Mail: bulatovic@mpdl.mpg.de
> phone: +49-89-38602-223
> fax: +49-89-38602-280
> 
> 
> 
Received on Sunday, 29 July 2012 12:18:07 UTC

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