Placement of @context in notification data

[Blobonat]

Hi,

I noticed a small deviation between Scorpio and Orion-LD with the placement of @context inside a notification with endpoint.accept: "application/ld+json": Orion-LD places the @context on the top level and Scorpio in data for each entity.

Orion-LD behavior:

{
  "id": "urn:ngsi-ld:Notification:7fe5040e-4865-11ed-95af-0242ac130006",
  "type": "Notification",
  "subscriptionId": "urn:ngsi-ld:Subscription:withAttributes",
  "@context": "https://fiware.github.io/data-models/full-context.jsonld",
  "notifiedAt": "2022-10-10T06:33:49.293Z",
  "data": [
    {
      "id": "urn:ngsi-ld:Vehicle:A500",
      "type": "Vehicle",
      "speed": {
        "type": "Property",
        "value": 80
      }
    }
  ]
}

Scorpio behavior:

{
  "id": "urn:ngsi-ld:Notification:7fe5040e-4865-11ed-95af-0242ac130006",
  "type": "Notification",
  "subscriptionId": "urn:ngsi-ld:Subscription:withAttributes",
  "notifiedAt": "2022-10-10T06:33:49.293Z",
  "data": [
    {
      "id": "urn:ngsi-ld:Vehicle:A500",
      "type": "Vehicle",
      "speed": {
        "type": "Property",
        "value": 80
      },
     "@context": "https://fiware.github.io/data-models/full-context.jsonld"
    }
  ]
}

I haven't found any requirement regarding the placement of the @context in the NGSI-LD API spec, but some FIWARE components such as Cosmos expect the format as used by Scorpio. Is there any way, e.g. the usage of a receiverInfo inside a subscription, to influence the format used by Orion-LD?

[kzangeli]

I guess we could put the @contexzt in either of the two positions (unless we add to the spec something we've been discussing in ETSI ISG CIM where the NGSI-LD API is defined - prohibiting the @context to be anywhere except the toplevel of a payload body).

In either case, if you receive a notification with 100 entities in the "data" array, and the @context is part of the items of that array, then you'd receive 100 copies of the exact same @context. That's an important waste of bandwidth and I'll talk to NEC about this. I'm confident they'll see my thinking and change Scorpio accordingly.

I'll post any news about this in this issue.

[kzangeli]

Just got the preliminary OK from NEC (owners of Scorpio) to do it "my way" - just preliminary for now. Well discuss this in ETSI ISG CIM and amend the API spec accordingly. A new release of the API spec is due just after Christmas, so it just might be part of that new version.

Once we have a definitive agreement, I'll post again (well, I'll try to remember!)