Implementors FAQ

This FAQ compilation is intended to clarify NGSI-LD specification by providing answers to common questions that implementors may have.

• Q: Could you give me some examples of NGSI-LD payloads?

  • R: See this test

• Q: What is a Property of a Property / Relationship?

• R: It is similar to NGSIv2 metadata. See https://github.com/Fiware/NGSI-LD_Tests/blob/master/contextProvision/create_entity_test.js#L132 'P1_P1' is a Property of 'P1'.

• Q: Property and Relationship can be arbitrarily nested?

• R: Yes, but only one or two levels could make sense in a real world scenario.

• Q: What is observedAt?

• R: It is the timestamp associated to a Property or Relationship. See https://github.com/Fiware/NGSI-LD_Tests/blob/master/contextProvision/create_entity_test.js#L88 . In NGSIv2 it was usually specified using the timestamp metadata member.

• Q: How geo-location is represented?

• R: See https://github.com/Fiware/NGSI-LD_Tests/blob/master/contextProvision/create_entity_with_ldcontext_test.js#L18 In essence a GeoProperty plus GeoJSON.

• Q: How DateTime is represented?

• R: See https://github.com/Fiware/NGSI-LD_Tests/blob/master/contextProvision/create_entity_with_ldcontext_test.js#L44

See also Supporting-DateTime

• Q: Is application/json supported as MIME type?

• R: Yes, indeed. However, the @context has to be externally provided, or no @context. In that case Entities will be under the Default @context. See https://github.com/Fiware/NGSI-LD_Tests/blob/master/contextProvision/create_entity_with_ldcontext_test.js#L18

• Q: What is the JSON-LD Link header?

• R:

• Q: Is the @context mandatory?

• R: For JSON-LD content, yes. (application/ld+json).

• Q: How terms are mapped to URIs?. Please explain the logic behind it.

• R:

• Q: What happens if an Entity Id is a URL?

• R: Nothing. Entity Ids have to be encoded.

• Q: Where I can find the default @context?

• R: https://fiware.github.io/NGSI-LD_Tests/ldContext/defaultContext.jsonld