Re: RSP Data Model

Hi Tara,
it seems I misunderstood the meaning of g, i thought it was an identifier
of the graph (a URI, or a bnode, as you pointed out). Now I better
understand your previous mail. Thanks for the clarification.

Daniele

Il giorno mer 17 giu 2015 alle ore 14:10 Tara Athan <taraathan@gmail.com>
ha scritto:

> On 6/15/15 10:28 AM, Daniele Dell'Aglio wrote:
>
> Hi Tara,
>
> Regarding this:
> > Elsewhere in the document, "triple" appears to be used as meaning "RDF
> triple". But in this case "triple" must mean
> > simply a tuple of size three, because RDF does not allow a graph to be
> the subject of an RDF triple.
>
>  Given that a graph is identified with a URI, it is possible to predicate
> on it, as in [1], example 10 (lines 27--29). It follows that (g, p, t) can
> be a RDF statement... do you see any problem with that?
>
>  Daniele
>
> [1] http://www.w3.org/TR/rdf11-primer/#section-trig
>
> Hi Daniele
>
> First, I question this assumption: "Given that a graph is identified with
> a URI". I don't think every time-stamped graph should be required to have
> the graph identified with an IRI, as in some cases, a blank node is
> sufficient. Requiring an additional IRI when it is not necessary puts a
> burden on fast transmission.
>
> Second, you are using 'g' as if it is an IRI but the semantics document
> says that 'g' *is* a graph. Let's be precise. To make an RDF triple, the
> subject must be an IRI or a blank node. It is possible to construct a
> triple (n, p, t) where "n" is an IRI or blank node that is the name of a
> named RDF graph pair (n, g). Such an RDF triple is not by itself an RDF
> Dataset, because it is also required to associate the name with the graph.
> However, this RDF triple could be the complete contents of the default
> graph of an RDF Dataset d, where d also contains one named graph (n, g).
>
> It is mathematically sound to talk about a tuple (g, p, t) where g is
> actually a graph, rather than the name of a graph. This structure can be in
> correspondence to an RDF Dataset, as above. But this tuple cannot itself be
> called an RDF Triple.
>
> Now if the intention is really that (g, p, t) is to be an RDF Triple, then
> g *denotes* a graph, rather than *being* a graph -- or it could denote a
> name-graph pair, depending on which variant of the semantics
> http://www.w3.org/TR/rdf11-datasets/#each-named-graph-defines-its-own-context
> is adopted. It is conventional to use "n" as the variable in that case
> rather than "g". Then the question arises: is a time-stamped graph really
> just this triple? Or is it an RDF Dataset where this triple is in the
> default graph? In the former case, then the IRI must be dereferenced or
> otherwise resolved to obtain the graph for querying. In the latter case,
> the named graph must be included in the stream in order to fully define the
> RDF Dataset.
>
> Finally, the RDF Primer is not intended to ever be normative. As such, it
> can contain statements that are not entirely precise, because it is about
> introducing newcomers to the ideas, not defining them. The TRIG
> specification (http://www.w3.org/TR/2014/REC-trig-20140225/) is a
> normative specification that defines a concrete syntax for RDF Datasets,
> and (rightly) says nothing about the semantics of RDF Datasets. But when we
> are defining the abstract model for a time-stamped graph, we should not be
> referring to any particular concrete syntax.  The RDF Dataset semantics is
> not yet an accepted recommendation, but it is the document most likely to
> progress to a recommendation, and I think it is the best choice for the
> foundation of time-stamped graph semantics.
>
> This whole discussion is relevant to the issue
> https://github.com/streamreasoning/RSP-QL/issues/10, but perhaps
> qualifies for an issue of its own.
>
>
> Tara
>
>
>
>
>  Il giorno lun 15 giu 2015 alle ore 15:16 Tara Athan <taraathan@gmail.com>
> ha scritto:
>
>>  On 6/15/15 5:30 AM, Gray, Alasdair J G wrote:
>>
>>  Hi Tara,
>>
>> On 14 June 2015 at 12:00:09, Tara Athan (taraathan@gmail.com) wrote:
>>
>>   Dear Abraham, and all -
>> Please excuse me if this point has already been discussed in the group,
>> as I am late joining the discussion.
>>
>>  Welcome to the discussion, the more the merrier.
>>
>>
>> It seems to me that there is an existing basis on which to build such a
>> data model - the RDF 1.1 dataset. The semantics for a set of time-stamped
>> graphs (g_i, p_i, t_i) that seems most appropriate to me is the one defined
>> here:
>>
>> http://www.w3.org/TR/rdf11-datasets/#each-named-graph-defines-its-own-context
>> and the name of each graph would be an implicit blank node that is also
>> the subject of a triple in the default graph. This triple has predicate p_i
>> and object t_i .
>>
>>  The discussion of the streaming graph data model came up at our recent
>> face-to-face meeting which is where we came up with the current data model
>> described in
>>
>> https://github.com/streamreasoning/RSP-QL/blob/master/Semantics.md
>>
>> As you will see in that document, we have exactly the semantics you are
>> suggesting.
>>
>>  I see this now - in the section "Timestamped Graph" - it is somewhat
>> hidden as RDF Datasets are not explicitly mentioned here. There is one
>> point especially about this definition that I find confusing:  '(g, p, t)'
>> is called a triple.
>>
>> Elsewhere in the document, "triple" appears to be used as meaning "RDF
>> triple". But in this case "triple" must mean simply a tuple of size three,
>> because RDF does not allow a graph to be the subject of an RDF triple.
>>
>> I have put this as well as a few other clarifications into a pull request
>> (https://github.com/streamreasoning/RSP-QL/pull/12) for purpose of
>> discussion.  I noticed that the pull request is already merged - I probably
>> should have made clear in my pull request comment that this was requested
>> for discussion, rather than immediate merge.
>>
>> Best regards, Tara
>>
>>  Alasdair
>>
>>
>>
>> Tara
>>
>> On 6/14/15 3:59 AM, Abraham Bernstein wrote:
>>
>> Dear Emanuele, dear all
>>
>>  I wonder whether we are mixing two issues here. One is the data model
>> of time-annotated graphs. The other is a system model that, as you
>> indicate, is much easier to deine if you can make some assumptions about
>> how the triples (or graph fragments) arrive (in order, monotonically
>> increasing, etc.).
>>
>>  I would propose to disentangle the two. In other words, I would propose
>> a well-founded time-based data model combined with a set of assertions that
>> we expect to hold on streams.
>>
>>  Best
>>
>>  Avi
>>
>>
>>
>>  On 12.06.2015, at 18:16, Emanuele Della Valle <
>> emanuele.dellavalle@polimi.it> wrote:
>>
>>  Dear Alasdair,
>>
>>  a problem I run into went I implemented the timestamped model in real
>> use cases is that you need to wait for all contemporaneous triples with the
>> same timestamp, before processing them. They arrive to the RSP engine one
>> after each other, so the arrival time is always increasing, but they all
>> carry the some timestamp. If you assume that timestamp are not decreasing,
>> an RSP engine knows it can start the processing as soon as a triple with a
>> larger timestamp arrives, but what if the stream stay silent? How does the
>> RSP engine distinguish the case of a delayed triple (still contemporaneous
>> to those it has already got) from the case it is waiting because nothing is
>> transmitted on the stream? In the C-SPARQL engine we decided to give up
>> with the possibility to treat the application time and we only relay on the
>> receiving time. This is also what STREAM does. It is know as the best
>> effort approach. Esper can work in best effort mode, but you can also send
>> an event to say the time is past. This is call external time control. This
>> time keeping event is a form of punctuation. It means, I told you all I
>> have to say at this point in time.
>>
>>  If graphs are timestamped with a strictly increasing timestamp, then as
>> soon as the RSP engine gets the entire graph, it can process it. In other
>> words, the boundary of the graph is a form of punctuation. If another graph
>> with the same timestamp can follow, than you’re back into the problem you
>> cannot distinguish if you are waiting for a delayed graph with the same
>> timestamp from the case the stream is silent.
>>
>>  I hope I expressed myself in a clearer way this time.
>>
>>  Best Regards,
>>
>>  Emanuele
>>
>>  PS I’m in favour of multiple time annotations and I agree that
>> interval-based semantics matters.
>>
>>
>>
>>
>>  On 12 Jun 2015, at 18:31, Gray, Alasdair J G <A.J.G.Gray@hw.ac.uk>
>> wrote:
>>
>>  Dear Emanuele,
>>
>>  I don’t quite follow the punctuation argument meaning that we can only
>> have one graph at any given time point.
>>  (Unfortunately I’m on the train home and cannot access the article that
>> you linked.)
>>
>>  We still have the gain over the traditional streaming RDF model in that
>> all triples conforming to a given observation will be contained in the
>> graph. So why does having more than one graph at a given time point cause a
>> problem?
>>  (Sorry if I am missing something obvious)
>>
>>  Best regards,
>>
>>  Alasdair
>>
>>  On 12 June 2015 at 08:49:40, Emanuele Della Valle (
>> emanuele.dellavalle@polimi.it) wrote:
>>
>>  Dear Alasdair, and all
>>
>>  thanks for the report. I would like to point out that the sentence
>> “There can be multiple graphs with the same timestamp” is, in my opinion, a
>> bad choice. It will prevent graphs to be interpreted as a form of
>> punctuation [1] and this was one of the most important gain of the version
>> of RSP Data Model discussed in Berlin (i.e., graphs with strictly
>> increasing timestamps). The lack of punctuation is a problem of the
>> “traditional" timestamped triples data model where contemporary triples
>> must be admitted.
>>
>>  Best regards,
>>
>>  Emanuele
>>
>>  [1]
>> http://link.springer.com/referenceworkentry/10.1007%2F978-0-387-39940-9_285
>>
>>
>>   On 11 Jun 2015, at 18:37, Gray, Alasdair J G <A.J.G.Gray@hw.ac.uk>
>> wrote:
>>
>>   Hi All,
>>
>>  During the ESWC RSP Workshop we had a breakout group focus on defining
>> the RSP data model. I was charged with the action of updating the semantics
>> document with the agreed model.
>>
>>  You can find the updated data model at
>>  https://github.com/streamreasoning/RSP-QL/blob/master/Semantics.md
>>
>>  Best regards,
>>
>>  Alasdair
>>
>>  --
>> Alasdair J G Gray
>> Lecturer, Heriot-Watt University
>> Web: http://www.alasdairjggray.co.uk
>> ORCID: http://orcid.org/0000-0002-5711-4872
>> Twitter: @gray_alasdair
>> Telephone: +44 131 451 3429
>> Office: EM 1.39
>>
>>
>>
>> We invite research leaders and ambitious early career researchers to join
>> us in leading and driving research in key inter-disciplinary themes. Please
>> see www.hw.ac.uk/researchleaders for further information and how to
>> apply.
>>
>> Heriot-Watt University is a Scottish charity registered under charity
>> number SC000278.
>>
>>
>>    --
>> Alasdair J G Gray
>> Lecturer, Heriot-Watt University
>> Web: http://www.alasdairjggray.co.uk
>> ORCID: http://orcid.org/0000-0002-5711-4872
>> Twitter: @gray_alasdair
>> Telephone: +44 131 451 3429
>> Office: EM 1.39
>>
>>
>>
>> We invite research leaders and ambitious early career researchers to join
>> us in leading and driving research in key inter-disciplinary themes. Please
>> see www.hw.ac.uk/researchleaders for further information and how to
>> apply.
>>
>> Heriot-Watt University is a Scottish charity registered under charity
>> number SC000278.
>>
>>
>>
>> -----------------------------------------------------------------
>> |  Professor Abraham Bernstein, PhD
>> |  University of Zürich, Department of Informatics
>> |  web: http://www.ifi.uzh.ch/ddis/bernstein.html
>>
>>
>>
>>
>>  --
>> Alasdair J G Gray
>> Lecturer, Heriot-Watt University
>> Web: http://www.alasdairjggray.co.uk
>> ORCID: http://orcid.org/0000-0002-5711-4872
>> Twitter: @gray_alasdair
>> Telephone: +44 131 451 3429
>> Office: EM 1.39
>>
>>
>>
>>  We invite research leaders and ambitious early career researchers to
>> join us in leading and driving research in key inter-disciplinary themes.
>> Please see www.hw.ac.uk/researchleaders for further information and how
>> to apply.
>>
>>  Heriot-Watt University is a Scottish charity registered under charity
>> number SC000278.
>>
>>
>>
>