11. Context Hosting

NGSI-LD Brokers optionally offer the capability to store and serve @contexts to clients. The stored @contexts may be managed by clients directly, via the APIs specified. Clients can store custom user @contexts at the Broker, effectively using the Broker as a @context server. Moreover, in order to optimize performance, NGSI-LD Brokers may automatically store and use the stored copies of common @contexts as a local cache, downloading them just once, thus avoiding fetching them over and over again at each NGSI-LD request. In order for the Broker to understand if a needed @context is already in the local storage or not, the Broker uses the URL, where the @context is originally hosted, as an identifier for it in the local storage.

There are following cases handles to manage @context server:

  • Cached : To be auto cached when broker request from external url, cached context will not be served by the broker on demand, and cached context should be invalidate after a fixed time.

  • Hosted : When user post @context, it need to be stored in database with a unique id.

  • ImplicitlyCreated : When a subscription body contains an array of contexts and notification is to be given in the form of application/json then these context should be hosted in broker and marked as implicitly created.

We can store @context to database and also download from other resource and store in the in-memory like cache memory.

11.1. Context Hosting Example

11.1.1. 1. Create Operation

In order to create an context, we can hit the endpoint POST http://<IP Address>:<port>/ngsi-ld/v1/jsonldcontext with the given payload.

Payload:

{
    "@context": {
        "stringproperty": "http://testdom.com/stringproperty",
        "intproperty": "http://testdom.com/intproperty",
        "floatproperty": "http://testdom.com/floatproperty",
        "complexproperty": "http://testdom.com/complexproperty",
        "testrelationship": "http://testdom.com/testrelationship",
        "TestType": "http://testdom.com/TestType"
    }
}

11.1.2. 2. Query Operation

  • Show the list of @contexts

To show the list of @contexts, you can send an HTTP GET request to - http://<IP Address>:<port>/ngsi-ld/v1/jsonldcontexts and we will get the list of contexts.

GET - http://localhost:9090/ngsi-ld/v1/jsonldcontexts

Response:

[
       "http://localhost:9090/ngsi-ld/v1/jsonldContexts/urn:9155d599-0db4-4fb0-91ba-4f478090b0fc"
]

  • Show the list of @contexts with context details

To show the list of @contexts with context details, you can send an HTTP GET request to - http://<IP Address>:<port>/ngsi-ld/v1/jsonldcontexts?details=true and we will get the list of contexts with context details.

GET - http://localhost:9090/ngsi-ld/v1/jsonldcontexts?details=true

Response:

[
    {
        "id": "urn:9155d599-0db4-4fb0-91ba-4f478090b0fc",
        "body": {
            "@context": {
                "TestType": "http://testdom.com/TestType",
                "intproperty": "http://testdom.com/intproperty",
                "floatproperty": "http://testdom.com/floatproperty",
                "stringproperty": "http://testdom.com/stringproperty",
                "complexproperty": "http://testdom.com/complexproperty",
                "testrelationship": "http://testdom.com/testrelationship"
            }
        },
        "kind": "hosted",
        "timestmp": "2023-02-09T11:10:07.707324",
        "url": "http://localhost:9090/ngsi-ld/v1/jsonldContexts/urn:9155d599-0db4-4fb0-91ba-4f478090b0fc"
    }
]

  • Show the list of @contexts with kind

To show the list of @contexts with kind either it can be Cached, Hosted or ImplicitlyCreated, you can send an HTTP GET request to - http://<IP Address>:<port>/ngsi-ld/v1/jsonldcontexts?kind=(kind} here we are getting contexts with kind=hosted, so we will get the list of contexts whose kind is equals to hosted.

GET - http://localhost:9090/ngsi-ld/v1/jsonldcontexts?kind=hosted

Response:

[
        "http://localhost:9090/ngsi-ld/v1/jsonldContexts/urn:9155d599-0db4-4fb0-91ba-4f478090b0fc"
]

  • Show the @context with particular URI

To show the @context with a particular URI, you can send an HTTP GET request to - http://<IP Address>:<port>/ngsi-ld/v1/jsonldcontexts/{id} and we will get the @context with particular URI.

GET - http://localhost:9090/ngsi-ld/v1/jsonldcontexts/urn:9155d599-0db4-4fb0-91ba-4f478090b0fc

Response:

{
        "@context": {
                "TestType": "http://testdom.com/TestType",
                "intproperty": "http://testdom.com/intproperty",
                "floatproperty": "http://testdom.com/floatproperty",
                "stringproperty": "http://testdom.com/stringproperty",
                "complexproperty": "http://testdom.com/complexproperty",
                "testrelationship": "http://testdom.com/testrelationship"
        }
}

  • Show the @context with particular URI and context details

To show the @context with a particular URI and context details, you can send an HTTP GET request to - http://<IP Address>:<port>/ngsi-ld/v1/jsonldcontexts/{id}?details=true and we will get the @context with particular URI and context details.

GET - http://localhost:9090/ngsi-ld/v1/jsonldcontexts/urn:9155d599-0db4-4fb0-91ba-4f478090b0fc?details=true

Response:

{
    "id": "urn:9155d599-0db4-4fb0-91ba-4f478090b0fc",
    "body": {
        "@context": {
            "TestType": "http://testdom.com/TestType",
            "intproperty": "http://testdom.com/intproperty",
            "floatproperty": "http://testdom.com/floatproperty",
            "stringproperty": "http://testdom.com/stringproperty",
            "complexproperty": "http://testdom.com/complexproperty",
            "testrelationship": "http://testdom.com/testrelationship"
        }
    },
    "kind": "hosted",
    "timestmp": "2023-02-09T11:10:07.707324",
    "url": "http://localhost:9090/ngsi-ld/v1/jsonldContexts/urn:9155d599-0db4-4fb0-91ba-4f478090b0fc"
}

11.1.3. 3. DELETE Operation

If we want to delete the @context, then we need to make DELETE request with the URL http://<IP Address>:<port>/ngsi-ld/v1/jsonldcontexts/{id}.

DELETE - http://localhost:9090/ngsi-ld/v1/jsonldcontexts/urn:9155d599-0db4-4fb0-91ba-4f478090b0fc