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## 5.5 NGSI-LD Value fragments

When updating or retrieving the value of an individual NGSI-LD Attribute, it is

necessary to have a means of describing the value to be updated. The value

_`null`_ or an NGSI-LD Null are prohibited within NGSI-LD Value fragments.

It is necessary to have a means of describing the value held within an

individual NGSI-LD Attribute. This is used when updating or retrieving the value

directly. In these cases, it shall be assumed that Entity ["id"]{.HTML-Code},

Entity ["type"]{.HTML-Code} and Attribute name can all be determined from the

operation signature.

A Value Fragment in the normalised format, shall at a minimum be a JSON Object

holding the mandatory elements of an Attribute as described in clause 5.3.2.2 -

["object"]{.HTML-Code}, ["languageMap"]{.HTML-Code}, ["vocab"]{.HTML-Code},

["valueList"]{.HTML-Code}, ["objectList"]{.HTML-Code} or ["json"]{.HTML-Code}.

Further members (such as ["datasetId"]{.HTML-Code}, ["observedAt"]{.HTML-Code})

where present, shall follow the data types described in clause

5.2.6.4.8. An optional ["@context"]{.HTML-Code} may also be present.

where present, shall follow the data types described in clause 5.2.6.4.8. An

optional ["@context"]{.HTML-Code} may also be present.

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according to the Normalized-to-Concise Compaction algorithm found in clause

5.3.2.2. However where present, the ["value"]{.HTML-Code} element shall not

undergo full compaction if the property value is a JSON primitive or GeoJSON

object, so that the ["value"]{.HTML-Code} element shall remain within the Fragment

object, so that the ["value"]{.HTML-Code} element shall remain within the

Fragment

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A Value Fragment in the simplified format, shall consist of a JSON Object

holding a representation of the Attribute value alone, and following the

compaction rules of the concise representation described above. An

["@context"]{.HTML-Code}, and in the Multi-attribute case ["datasetId"]{.HTML-Code}

may also be present.

["@context"]{.HTML-Code}, and in the Multi-attribute case

["datasetId"]{.HTML-Code} may also be present.

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When updating or retrieving the value of an individual NGSI-LD Attribute, it shall

be assumed that Entity [id"]{.HTML-Code}, Entity ["type"]{.HTML-Code} and Attribute

name can all be determined from the operation signature.

Where the binding explicitly defines a request or response to be **value only**,

the NGSI-LD Value Fragment shall be represented purely as a value (e.g. a JSON Primitive)

rather than as a JSON Object.

Where a binding explicitly defines a request or response to be **value only**,

the representation of an NGSI-LD Value Fragment changes, and shall be

represented purely as the Attribute value itself (e.g. directly as a JSON

Primitive, a JSON Object or JSON Array as necessary) rather than as a JSON

object holding a series of key-value pairs as described above.

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An _`@context`_ cannot be embedded within the NGSI-LD Value fragment when using

the **value only** representation, therefore in this case, whenever an

_`@context`_ is required, it shall be supplied through the use of a Link header

(see Clause+++clause-6+++6.2.4).

The value _`null`_ or any representation of NGSI-LD Null are prohibited within

NGSI-LD Value fragments.