Re: How to avoid that collections "break" relationships (ISSUE-41) (was: hydra:Link)

On Mar 24, 2014, at 8:14 AM, "Markus Lanthaler" <markus.lanthaler@gmx.net> wrote:
> 
> Changing the subject line
> 
>> On Friday, March 21, 2014 5:45 PM, Gregg Kellogg wrote:
>>> On Mar 21, 2014, at 7:52 AM, Markus Lanthaler wrote:
>>>> On Wednesday, March 19, 2014 10:44 PM, Gregg Kellogg wrote:
>>>> </GreggKellogg> a foaf:Person;
>>>> foaf:knows
>>>>   [a foaf:Person; is hydra:member of </GreggKellogg/colleagues>],
>>>>   </MarkusLanthaler> .
>>>> 
>>>> <MarkusLanthaler> a foaf:Person .
>>> 
>>> Hmm... I think this is a bit too clever and still creates a triple
>>> that you don't want.
>> 
>> The notation is clever, just because Turtle doesn't allow me to express
>> this. The notation in JSON-LD is straightforward IMO.
> 
> I think I disagree. You point to a blank node which is only there to be
> referenced by the collection (in contrast to point to the collection) that
> you are actually looking for. That's a bit too much magic IMHO.
> 
> 
>> The concept of indirecting through another resource is basically a
>> property path; it may be sophisticated, but it avoids asserting
>> unnecessary triples (at least with IRI subjects). It does create
>> additional BNode-subject triples, but in the context of Linked Data,
>> these can be seen as necessary "semantic glue", and are easily
>> filtered.
> 
> Well, everything is "easily filtered".. it doesn't really matter whether
> it's a blank node or not I'd say.

> [...]
> 
>>> While I don't really like the specific blank node solution you are
>>> proposing, I find the principle quite interesting. We could avoid the
>>> blank node, and thus a triple we don't want, entirely but just
>>> including a member of collection directly:
>>> 
>>>   {
>>>     "@context": {
>>>       "foaf": "http://xmlns.com/foaf/0.1/",
>>>       "hydra": "http://www.w3.org/ns/hydra/core",
>>>       "memberOf": { "@reverse": "hydra:member" }
>>>     },
>>>     "@id" "GreggKellogg",
>>>     "foaf:knows": {
>>>       "@id": "MarkusLanthaler,
>>>       "memberOf": "GreggKellogg/colleagues"
>>>     }
>>>   }
>>> 
>>> WDYT?
>> 
>> This would work fine, except for empty collections.
> 
> Good point!
> 
> 
>> I would settle on
>> this as a compromise if the BNode-based relationship I suggested is not
>> palatable. Personally, I think the use of a BNode is a better call to
>> dereference the memberOf relation to get values, whereas filling in on
>> value might not make it clear that it is just a single representative
>> member of such a collection.
> 
> I don't have a problem with the blank node per se but find the use of a
> reverse property quite confusing in this instance. Maybe we should consider
> creating a more explicit description of the collection instead. Something
> along the lines of
> 
>    "@id" "/GreggKellogg/colleagues",
>    "managing": {
>      "subject": "/GreggKellogg/",
>      "property": "foaf:knows"
>    },
>    "member": [
>      { "@id": "/MarkusLanthaler" }
>    ]
> 
> We could then even define a simple inference rule such as ?member =>
> ?subject ?property ?member

That works for describing the collection itself, but not the reference to the collection. What did you have in mind here? Perhaps an operation?

>> Considered as a SPARQL query, the use of a BNode indirection is
>> something like the following:
>> 
>> SELECT ?member ?p ?o
>> WHERE {
>>  </GreggKellogg> a foaf:Person .
>>  ?container hydra:member ?member .
>>  ?member ?p ?o .
>> }
>> 
>> Which has a certain appeal to me.
> 
> I'm not sure what you want to illustrate with this SPARQL query.. copy and
> paste error?

It's missing </GreggKellogg> foaf:knows ?member .

What it's attempting to illustrate is I can get all the triples that where the subject has a foaf:knows relationship with the person. It also gets the collection which references them, although I didn't use it in the query results. The point is using variables here, which we can't do in turtle, so bnodes are the closest approximation. But, if I'm a lone voice in the wilderness, let's just move on.

Gregg

>> I'd like to hear other people's thoughts on the merits of a direct
>> collection relationship vs. an indirect relationship, and the problem
>> that asserting a Collection as the value of a property who's range is
>> something else presents.
> 
> Me too. I'll send a separate mail to public-lod and public-vocabs (of course
> cc'ing this group) to get more opinions.
> 
> 
> 
> --
> Markus Lanthaler
> @markuslanthaler
>

Received on Monday, 24 March 2014 17:41:17 UTC