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Re: Inverse properties in Turtle

From: Gregg Kellogg <gregg@greggkellogg.net>
Date: Sat, 11 Aug 2012 23:30:57 -0400
To: Andy Seaborne <andy.seaborne@epimorphics.com>
CC: Pat Hayes <phayes@ihmc.us>, "public-rdf-comments@w3.org" <public-rdf-comments@w3.org>
Message-ID: <AF51513B-C757-4C4D-9627-F1A33CE53599@greggkellogg.net>
(retry, without typos!)

On Aug 11, 2012, at 1:11 PM, Andy Seaborne <andy.seaborne@epimorphics.com> wrote:

> On 11/08/12 19:40, Steve Harris wrote:
>> On 11 Aug 2012, at 18:02, Pat Hayes wrote:
>>> On Aug 11, 2012, at 5:22 AM, Andy Seaborne wrote:
>>>> Hi Dan,
>>>> On 11/08/12 07:46, Dan Brickley wrote:
>>>>> Hi Dave,
>>>>> On 10 August 2012 19:25, Dave Beckett <dave@dajobe.org> wrote:
>>>>>> Dear RDF Working Group
>>>>> (Just a personal response here)
>>>> Ditto.
>>>>> Agreed. This is a niche topic, but I still now thing it is of
>>>>> occasional use.
>>>>> In particular, as a maintainer/editor/contributor for popular
>>>>> RDF vocabularies (FOAF, schema.org and others) I believe there
>>>>> is implicit demand for this which is often expressed instead in
>>>>> terms of requests for new inversely named properties. Whenever
>>>>> someone asks a vocabulary maintainer to add 'isDirectorOf'
>>>>> alongside 'director', or asks what the inverse of 'actor', or
>>>>> 'associatedAnatomy' or 'depicts' is, they are talking about
>>>>> just this issue.
>>>> For those people, do you think "^" will read acceptable to those
>>>> people?  (Your point about "isXof" not always being the best
>>>> choice of name is also interesting.)
>>>>>> 3. It is not in SPARQL's data syntax. 4. There is a high bar
>>>>>> to add a new feature to an existing, well understood and
>>>>>> implemented language like Turtle.  This feature does not fit
>>>>>> that in my judgement.
>>>>> Taking those two together, ...
>>>>> I only support adding such a construct if it has a comparable
>>>>> notation in SPARQL. They might not be 100% identical, but the
>>>>> basic concept ought to either be in both, or in neither. Turtle
>>>>> and SPARQL share a common heritage in N3; if we can make
>>>>> teaching them (Turtle and SPARQL; I consider N3 something like
>>>>> a "Labs project") easier by sharing structure and ideas, we
>>>>> ought to.
>>>> A difference between "^:directory" (or the "is...of" syntax) and
>>>> a property :isDirectorOf is that the "^" solution immediately
>>>> does the reversing of the written subject and written object.
>>>> :Ridley_Scott ^:director :Blade_Runner
>>>> leading to a possible unexpected situation later:
>>> POSSIBLY unexpected. If someone were under the illusion that the
>>> caret syntax created a new property, they would be surprised or
>>> disappointed at this point. The answer, surely, is to take pains,
>>> in writing the documentatio, to explain carefully that it does not
>>> do this. Your example would be a good one to use is such a
>>> tutorial, for example. But the fact that a feature MIGHT be
>>> surprising to someone who DIDNT read the tutiorials and does not
>>> understand it, it surely not a good argument for not including it.
> I'm undecided about this feature; I haven't seen a complete proposal 
> yet.  There is not absolute argument one way or the other that I've seen 
> and it seems to come down to a value judgement.
> What does not work for me in this case is the argument like
>  Use Case -> feature solves Use Case -> include feature.

Case #1

For one thing, it would mean that a Turtle serialization of a SPARQL DESCRIBE (at least one using a Concise Bounded Description) could be generated with a single "subject". For a describe of :gregg in the graph

:gregg foaf:knows :andy .
:andy foaf:knows :gregg .

could be serialized as

:gregg foaf:knows : andy; ^foaf:knows :andy .

Case #2

The second scenario I've seen is where several resources need to be declared as having the same type.

foaf:Person ^a :gregg, : andy .

Personally, I prefer is..of, and suggest that we include that as syntactic suggar:

foaf:Person is rdf:type of :gregg, :andy

Reads much better. (Not so much in the first use case).


> I agree the use case is real and the feature addresses the use case but 
> it isn't a feature someone can simply ignore if they don't like or don't 
> understand it because this is the web so it can appear in data from 
> elsewhere.
> Syntax matters to some people, maybe not you, maybe not me. I think that 
> includes people who will be using this technology and a whole host of 
> other technologies. Web developers. They can not be expected to have a 
> complete recall of every feature.
> It does give object-like effects (design depending) to the actual 
> subjects because of syntax:
> :Ridley_Scott ^:director :Blade_Runner , :A_Good_Year ;
>              rdfs:seeAlso <http://www.imdb.com/name/nm0000631/> .
> "Ridley Scott" ^foaf:name <http://www.imdb.com/name/nm0000631/> .
> the latter does rather hint at literals-as-subjects.
> 	Andy
>> If someone were of that illusion, or if they simply missed it
>> lexically, or didn't know what it means.
>> Regardless, this will make Turtle harder to teach. I don't have a
>> feeling for how much harder.
>> - Steve
Received on Sunday, 12 August 2012 03:31:37 UTC

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