[Fiware-ngsi] Association in NGSI

[fano.ramparany at orange.com]

Hi Tobias and all,

I understand your point for the list example. Well IMHO, specifying individual ContextRegistration for each association avoid ambiguity and misinterpretation, compared to doing a collective ContextRegistration using lists :). But as far as this is documented in the user manual, this is OK.

Best regards,

Fano

De : Tobias Jacobs [mailto:Tobias.Jacobs at neclab.eu]
Envoyé : jeudi 7 mars 2013 12:05
À : RAMPARANY Fano OLNC/OLPS; Fermín Galán Márquez; fiware-ngsi at lists.fi-ware.eu
Objet : RE: [Fiware-ngsi] Association in NGSI

Hi Fano,

I think what the description clearly is missing are more examples. I still would like additionally to keep the formal definitions, as they are, well, formal :).

To explain the second point, let me make an example where I use strongly simplified NGSI terminology.
Assume the following ContextRegistration:

EntityIdList: Sensor1, Sensor2
AttributeList:
          Temperature1
                    Metadata AttributeAssociation: Room1.temperature
          Temperature2
                    Metadata AttributeAssociation: Room2.temperature

This ContextRegistration expresses all attributeAssociations withone combining an Entity from the EntityId, an Attribute from the AttributeList and some piece of metadata inside the Attribute. So in this case, the following associations are expressed

Sensor1.Temperature1 --> Room1.temperature
Sensor1.Temperature2 --> Room2.temperature
Sensor2.Temperature1 --> Room1.temperature
Sensor2.Temperature2 --> Room2.temperature

Now how can we express only the 1st and the 3rd of these associations, avoiding the unintended other two associations? By using two individual ContextRegistrations:

EntityIdList: Sensor1
AttributeList:
          Temperature1
                    Metadata AttributeAssociation: Room1.temperature

EntityIdList: Sensor2
AttributeList:
          Temperature2
                    Metadata AttributeAssociation: Room2.temperature

Best
Tobias


From: fano.ramparany at orange.com [mailto:fano.ramparany at orange.com]
Sent: Donnerstag, 7. März 2013 11:46
To: Tobias Jacobs; Fermín Galán Márquez; fiware-ngsi at lists.fi-ware.eu
Subject: RE: [Fiware-ngsi] Association in NGSI

Hi Tobias and all,

Thank you for your feedback. Mine inline tagged [Fano(new):].

De : fiware-ngsi-bounces at lists.fi-ware.eu<mailto:fiware-ngsi-bounces at lists.fi-ware.eu> [mailto:fiware-ngsi-bounces at lists.fi-ware.eu] De la part de Tobias Jacobs
Envoyé : jeudi 7 mars 2013 10:43
À : Fermín Galán Márquez; fiware-ngsi at lists.fi-ware.eu<mailto:fiware-ngsi at lists.fi-ware.eu>
Objet : Re: [Fiware-ngsi] Association in NGSI

 ...
[Tobias:] If entity1, entity2, entity3 appear as metadata of type EntityAssociation and entityA appears in the EntityIdList of the ContextRegistration, then this expresses the associations entityA --> entity1, entityA --> entity2, entityA --> entity3. But it does not express any association like e.g. entity1 --> entity2.

This is expressed by the sentence
"Let in a ContextRegistration structure M be the set of EntityIDs appearing in such a type of metadata, and let E be the set of EntityIDs appearing in the EntityIdList. Then this ContextRegistration represents all associations of the form <entityId_1> --> <entityId_2>, where <entityId_1> is contained by E and <entityId_2> is an element of M."
But maybe the language is too mathematical to be understandable? Would you express it differently?

[Fano(new):] I admit that I understand better your first formulation above than your second one.
...


-          [Fano:]  A list of attribute associations is easier to understand though, if it is a way to express in one registration several independent attribute associations (one for each element of the list). Is there something else to understand about a list of attribute associations?
[Tobias:] Not sure if I understand your question right.
You can register more than one association in the same contextRegistration structure. but you the sets of associations cannot be chosen arbitrarily. This is because e.g. expressing
sensor1.measurement1 --> room1.temperature and
sensor2.measurement2 --> room2.temperature
in the same contextRegistration structure is not possible without at the same time expressing the associations
sensor2.measurement1 --> room1.temperature and
sensor1.measurement2 --> room2.temperature.
Of course it is still possible to register exactly the first two associations, but two different contextRegistration structures are needed for this.

[Fano(new):] Obviously I missed important points in my understanding. Could you please explain why the two first attribute associations requires the two following ones to be registered? Suppose that sensor1 is a simple thermometer located in room1 and sensor2 is another thermometer located in room2. Then these thermometer sensors produce a single measurement (measurement1 and measurement2 are the same "namewise"). We then have:
Thermometer1.measurement -> room1.temperature and
Thermometer2.measurement -> room2.temparature
In this case we don't have:
Thermometer2.measurement -> room1.temperature and
Thermometer1.measurement -> room2.temperature
Unless room1 and room2 are the same room with different names.

Best regards,

Fano







From: fiware-ngsi-bounces at lists.fi-ware.eu<mailto:fiware-ngsi-bounces at lists.fi-ware.eu> [mailto:fiware-ngsi-bounces at lists.fi-ware.eu] On Behalf Of Fermín Galán Márquez
Sent: Dienstag, 5. März 2013 20:23
To: fiware-ngsi at lists.fi-ware.eu<mailto:fiware-ngsi at lists.fi-ware.eu>
Subject: Re: [Fiware-ngsi] Association in NGSI

Dear Tobias, all,

Sorry for the delay sending the answer. It has take some time to read in deep your proposal and having a look to the discussion that followed it in the list (unfortunately, I haven't follow in deep so far the discussion by email, in the hope any relevant conclusion will be re-injected to the wiki page at the end).

We will need to discuss internally in TID the implications of this proposal (mainly in the implication side). However, in the meanwhile, let me ask some questions to clarify some points:

  *   Do the entities/attributes referred by the association registerContext (at both ends of the association) need to have been registered before? I mean, in your example, the Sensor_123-temperature, RoomB-temperature and RoomA elements need to have been previously registered? Otherwise, you will create an association between elements that does't "exists" in the database managed by the NGSI9 server...
  *   You describe basically association creation and query, but what about association modifications and deletion? Are these cases considered in the scope of your proposal?
  *   Could you detail the example of discoverContextAvailability introduced in the "Usage in NGSI9 operations" section in the wiki? I mean, what should be sent as discoverContextAvailabilityResponse in the following cases:

     *   discoverContextAvailability on <entityId_1>.<attributeName_1>
     *   discoverContextAvailability on <entityId_2>.<attributeName_2>

  *   Is NGSI10 out of the scope of your proposal?

Thanks!
Best regards,

------
Fermín

El 01/03/2013 12:09, Tobias Jacobs escribió:
Dear all,

As promised, we have worked out a concept to represent associations between context entities in NGSI.

This is an important feature of the IoT Backend, and in particular relevant for the interaction between Configuration Management and IoT Broker.

If you are interested in this topic, please read our draft at
https://forge.fi-ware.eu/plugins/mediawiki/wiki/fi-ware-private/index.php/OMA_NGSI_Association_concept.
It is a rather short document.

I am looking forward to the discussion about this topic :)

Best regards
Tobias


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