Re: RSP Data Model

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 
> <mailto: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 
>>>> <mailto: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 
>>>>> <mailto: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 
>>>>> <mailto: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 <mailto: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 
>>>>>>> <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 
>>>>>>> seewww.hw.ac.uk/researchleaders 
>>>>>>> <http://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 
>>>>> <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 seewww.hw.ac.uk/researchleaders 
>>>>> <http://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.