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Re: Issue-89, proposal 3: Duplication of triples & inferencing

From: Henry Story <henry.story@bblfish.net>
Date: Fri, 13 Dec 2013 19:58:14 +0100
Cc: Linked Data Platform WG <public-ldp-wg@w3.org>, sysreq@w3.org
Message-Id: <2ED874F0-22E5-40D5-BDEC-F37872CD6802@bblfish.net>
To: Arnaud LeHors <lehors@us.ibm.com>

On 13 Dec 2013, at 17:41, Arnaud Le Hors <lehors@us.ibm.com> wrote:

> Thanks Roger for expressing yourself. 
> 
> I have to say that I'm surprised by Henry's take on this. First, the example being discussed isn't new at all. We've been talking about this from the very beginning. Again, it is very disruptive to start questioning these so late in the game.

Things have changed in the spec. We recently introduced the ldp:SimpleContainer, ldp:DirectContainer, and 
the ldp:IndirectContainer. The examples in the primer need to be adjusted for this new reality. That's all 
I am doing.

> Second, I don't think there is much future in arguing that other people's use cases aren't valid on the basis that their data isn't structured properly or any other reasons.

You misunderstand me. I am not arguing about the validity of the use case at all. 
In fact I showed that the same use case can be achieved with the newly 
voted ldp:SimpleContainer in a much more elegant fashion. 
Is this not what a Primer should do?

> People have different needs and the only way forward is to accept that and try to address them equally rather than disqualify them. 
> 
> For these reasons I don't see any value in entertaining such a discussion. 

Good so given that I was not trying to disqualify a use case, but show how one could use
the tools we have to improve the implementation of it, can we continue the discussion? 


Henry

> --
> Arnaud  Le Hors - Software Standards Architect - IBM Software Group
> 
> 
> 
> 
> From:        Roger Menday <roger.menday@uk.fujitsu.com> 
> To:        Henry Story <henry.story@bblfish.net>, 
> Cc:        Steve K Speicher <sspeiche@gmail.com>, Arnaud Le Hors/Cupertino/IBM@IBMUS, Linked Data Platform WG <public-ldp-wg@w3.org> 
> Date:        12/13/2013 07:59 AM 
> Subject:        Re: Issue-89, proposal 3: Duplication of triples & inferencing 
> 
> 
> 
> 
> Henry, 
> 
> Whilst the path between a product and a bug is probably something like:   
> 
>    product --hasbug--> bug 
> 
> ... you are saying: 
> 
>    product  --bugreportcollection-->  bugcollection  --ldpcontains-->  bug 
> 
> I have a number of problems with this. 
> For a start, this becomes more difficult to query. 
> 
> thanks, 
> Roger 
> 
> 
> 
> On 12 Dec 2013, at 22:28, Henry Story wrote: 
> 
> On 12 Dec 2013, at 21:26, Steve Speicher <sspeiche@gmail.com> wrote: 
> 
> Hi Henry,
> 
> Let me try to reiterate the use case we've discussed.
> 
> On Thu, Dec 12, 2013 at 2:01 PM, Henry Story <henry.story@bblfish.net> wrote:
> >
> >
> > On 12 Dec 2013, at 19:20, Arnaud Le Hors <lehors@us.ibm.com> wrote:
> >
> > > While true, it's been pointed out before, several times, that this would fall short of addressing the use case at hand: allowing one to define a container over existing data by leveraging a domain specific vocabulary.
> >
> > I am not sure I understand. The use case is I suppose that one should
> > be able to publish existing data using LDP. It can't be a requirement
> > to publish the data in an LDPC in particular.
> >
> > It seems obvious that one can publish any data in an LDPR ( that is not
> > an LDPC of course ). So the use case is satisfied anyway.
> >
> > Can anyone explain in particular why the data MUST be placed in an
> > LDPC?
> 
> Because that how my model structured being part of a container-like structure, prior to LDP spec, and I want to apply LDP to it.  I shouldn't need to setup a LDPC to the side of my model but apply to it.  Take example 6 from the primer[1], it is an example of this.   
> 
> Example 6 from the primer is very badly modelled. It is confusing the LDPContainer with a product. 
> Unless the product is the container itself, in which case it is a very odd container that has so many bugs. 
> (I would not use a container that has so many bugs). 
> 
> Presumably the  product should be something other than the container. It would then need 
> another LDPG that can describe that product, in order to make it easy for a client to edit 
> ( using PATCH ) without getting confused about relations that are managed by the container 
> - such as ldp:xyz, a.k.a. ldp:contains relations - and those that are relations about the product 
> ( such as its size, its date of creation, its owner, its price, etc, and that may be managed by human 
> managers ). 
> 
> So  we could have the following resources 
> 
> </app/product1>           <-   the document about the product 
> </app/product1#v1>     <-   the real product 
> </app/product1/bugs/> <-   the bugs about the product 
> 
> You don't even need anything more than a ldp:SimpleContainer as 
> I can show below: 
> 
> The product description can be found with the following 
> 
> [[ 
> GET /app/product1 
> 
> <#v1> a   
>     dc:title "Semantic Web For the Working Ontologist"; 
>     shop:price "38"^^currency:dollars; 
>     bt:bugReportCollection <bugs/> .     
> ]] 
> 
> The bugs collection linked from the product can also be found by following 
> your nose from above: 
> 
> [[ 
> GET /app/product1/bugs/ 
> 
> <../product1> bt:bugReportCollection <> . 
> <> a ldp:SimpleCollection; 
>      ldp:contains <bugReport1>, <bugReport2>, <bugReport3> . 
> ]] 
> 
> 
>  Looking at that  </app/product1/bugs/> collection one can find what product is the subject of the collection. 
>  POSTing to /app/product1/bugs creates new bug reports 
>  DELETEing a bug report is the understood way to remove it from the LDPC 
>  There is no duplication of triples here anywhere 
> 
> 
> Additional context is that there are a number of data sources that expose similar models (servers emitting Linked Data resources).  So basically it has membership predicate bt:hasBug, you can infer ldp:xyz from it.  Using the approach Henry outlined below it opposite what I need.  I already know the membership triples. 
> 
> If I map this to programming languages this seems like what you are saying is that a List or a Set is not enough 
> to represent a collection, that you need the relations in each list to be a different type of relation. 
> 
> But usually in programming languages one models such things by creating an object with an attribute to a collection 
> of things. Eg: 
> 
> { 
>   name: "Semantic Web For the Working Ontologist"; 
>   bugs: [ bug1, bug2, bug3 ]; 
> } 
> 
> where the collection [ bug1, bug2, bug3 ] here is a list, where the relation from one member of the list 
> to the next is always the same relation ( e.g.: rdf:first, rdf:next ). 
> 
> Here for some reason you seem to be requiring that each collection have a different 
> type of relation, but that the subject of the collection be an LDPC and the object be an LDPR. 
> There are so many other ways of modelling this that seem to be better, and that would 
> make the specification simpler, and the work of clients easier. 
> 
> 
> We've already cover this use case quite a bit.  I believe for DirectContainers, the ldp:xyz could be inferred for those clients that need it.  Instead of requiring that burden on all servers to explicitly produce these (c, ldp:xyz, mr) triples that are very simple for those clients that need it to produce it. 
> 
> I think I show above that you get what you want without the need for DirectContainers, without the need for duplicationg relations, 
> and without needing clients to do odd inferencing. 
> 
> 
> [1] - https://dvcs.w3.org/hg/ldpwg/raw-file/tip/ldp-primer/ldp-primer.html 
> 
> 
> 
> 
> - Steve Speicher 
> 
> >
> >
> > > It's this new relationship that should be inferred.
> > > --
> > > Arnaud  Le Hors - Software Standards Architect - IBM Software Group
> > >
> > >
> > > Henry Story <henry.story@bblfish.net> wrote on 12/12/2013 09:27:28 AM:
> > >
> > > > From: Henry Story <henry.story@bblfish.net>
> > > > To: Linked Data Platform WG <public-ldp-wg@w3.org>,
> > > > Date: 12/12/2013 09:31 AM
> > > > Subject: Issue-89, proposal 3: Duplication of triples & inferencing
> > > >
> > > > Part 3 of Issue-89 creates a relation ldp:propertiesOnlyResource
> > > > to allow an LDPC to point in its header to the "membership properties".
> > > > The reason for this is to avoid so called duplication of triples.
> > > >
> > > > The duplication of triples is an issue mostly for the
> > > > ldp:DirectContainer as is visible for a container such
> > > > as the following
> > > >
> > > > <> a ldp:DirectContainer;
> > > >         ldp:containerResource <>;
> > > >         ldp:containsRelation m:manages;
> > > >     ldp:xyz <doc1>, <doc2>, <doc3> ;
> > > >     m:manages <doc1>, <doc2>, <doc3> .
> > > >
> > > > ( I am using ldp:xyz for what alexander in ISSUE-89 calls
> > > >   ldp:contains. You can replace it without loss here and
> > > >   throughout this e-mail. )
> > > >
> > > > But according to the rule such as the one used in the Membership wiki [1]
> > > > it would be very easy to determine the "membership triples" using only
> > > > the ldp:xyz relations
> > > >
> > > > PREFIX ldp: <http://www.w3.org/ns/ldp#>
> > > >
> > > > CONSTRUCT { ?subject ?predicate ?object }
> > > > WHERE {
> > > >    ?ldpc a ldp:DirectContainer;
> > > >         ldp:containerResource ?subject;
> > > >         ldp:containsRelation ?predicate;
> > > >
> > > >    ?ldpc ldp:xyz ?document .
> > > >    BIND (?document AS ?object)                             # the
> > > > POSTed resource is the member
> > > >  } UNION {
> > > >    ?ldpc a ldp:DirectContainer;
> > > >         ldp:containerResource ?object;
> > > >         ldp:containedByRelation ?predicate.                   #
> > > > ldp:containedByRelation is used
> > > >
> > > >    ?ldpc ldp:xyz ?document .
> > > >    BIND (?document AS ?object)
> > > >  }
> > > > }
> > > >
> > > > In that case duplication is not a problem at all,
> > > > since a client could just infer the "membership triples"
> > > > from the ldp:xyz ones using that query.
> > > >
> > > > On the other hand if such a rule is not true, and cannot
> > > > be written out, then there is no duplication, since the
> > > > "membership triples" are in fact different triples, and
> > > > have no necessary relation to the ldp:xyz ones.
> > > >
> > > > But then this does give one a good reason for having them in a
> > > > different possibly server managed resource.
> > > >
> > > >
> > > >
> > > >
> > > > [1]in the Membership wiki "Determining the membership  triples to be
> > > > added when a new member
> > > > is created"  http://www.w3.org/2012/ldp/wiki/
> > > > Membership#Determining_the_membership_triples_to_be_added_when_a_new_member_is_created
> > > >
> > > >
> > > > Social Web Architect
> > > > http://bblfish.net/
> > > >
> > > >
> >
> > Social Web Architect
> > http://bblfish.net/
> >
> > 
> 
> Social Web Architect 
> http://bblfish.net/ 
> 
> 

Social Web Architect
http://bblfish.net/
Received on Friday, 13 December 2013 18:58:51 UTC

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