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Implementors FAQ
This FAQ compilation is intended to clarify NGSI-LD specification by providing answers to common questions that implementors may have.
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Q: Could you give me some examples of NGSI-LD payloads?
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Q: What is a Property of a Property / Relationship?
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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'.
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Q: Property and Relationship can be arbitrarily nested?
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R: Yes, but only one or two levels could make sense in a real world scenario.
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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
timestampmetadata member. -
Q: How geo-location is represented?
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Q: How DateTime is represented?
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R: See https://github.com/Fiware/NGSI-LD_Tests/blob/master/contextProvision/create_entity_with_ldcontext_test.js#L44 In essence a
GeoPropertyplus GeoJSON. -
Q: Is
application/jsonsupported as MIME type? -
R: Yes, indeed. However, the
@contexthas 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?
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R:
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Q: Is the @context mandatory?
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R: For JSON-LD content, yes. (
application/ld+json). -
Q: How terms are mapped to URIs?. Please explain the logic behind it.
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R:
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Q: What happens if an Entity Id is a URL?
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R: Nothing. Entity Ids have to be encoded.
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Q: Where I can find the default @context?
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R: https://fiware.github.io/NGSI-LD_Tests/ldContext/defaultContext.jsonld