Added in error

#### 10.2.6.1 Description

This operation allows the modification of the value of an **already existing**

Attribute of an **existing** NGSI-LD Entity.

#### 10.2.6.2 Use case diagram

A [Context Producer]{.HTML-Keyboard} can set the value of an existing Attribute

within an NGSI-LD system as shown in Figure+++below.

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<img src="media/set-attribute-value-use-case.svg"/>

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::: TF

Figure: Set Attribute Value use case

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#### 10.2.6.3 Input data

- Entity ID (URI) of the concerned Entity, the target Entity.

- A selector of Entity types as specified by clause 7.2.2 (optional).

- Target Attribute to be modified, identified by a name.

- A JSON or JSON-LD document representing an NGSI-LD Attribute Fragment (see

  clause 5.4.2)

- An optional parameter indicating an _`observedAt`_ timestamp to use when

  setting the Attribute value.

- An optional parameter indicating a _`datasetId`_ to use when setting the

  Attribute value.

#### 10.2.6.4 Behaviour

- If the target Entity ID is not a valid URI or it is not present, then an error

  of type [BadRequestData]{.HTML-Error} shall be raised.

- If the target Attribute name is not valid or it is not present, then an error

  of type [BadRequestData]{.HTML-Error} shall be raised.

- If the target Attribute is _`scope`_, then an error of type

  [BadRequestData]{.HTML-Error} shall be raised.

- If the request payload body is not a valid JSON document or the payload body

  contains [null]{.HTML-Code} or ["urn:ngsi-ld:null"]{.HTML-Code}, then an error

  of type [InvalidRequest]{.HTML-Error} shall be raised.

- If the NGSI-LD endpoint does not know about the target Entity, because there

  is no existing Entity whose id (URI), and where specified type, is equivalent

  held locally, and no matching registrations apply (see clause 9.4), then an

  error of type [ResourceNotFound ]{.HTML-Error} shall be raised.

- If an **exclusive** or **redirect** [Context Source

  Registration]{.HTML-Keyboard} matches against the input data, the payload body

  is forwarded for remote processing. For each matching registration:

  - If the Set Attribute Value operation is supported by the registration (see

    clause 9), matching input data is forwarded to the Registration endpoint.

  - If the Aet Attribute Value operation is not supported by the registration,

    this shall result in an error of type [Conflict]{.HTML-Error} in case the

    complete set Attribute value failed, or in a partial success if some parts

    of the set Attribute value succeeded.

    No further processing is required.

- For any **inclusive** [Context Source Registrations]{.HTML-Keyboard} that

  match against the input data, that input data is also forwarded for remote

  processing to matching endpoints in case the set Attribute value operation is

  supported.

- Apply term expansion as mandated by clause 8.2.4, so that the fully qualified

  name (URI) associated to the target Attribute is properly obtained.

- If the target Entity does not contain the target Attribute:

  - as a default instance in case no _`datasetId`_ is present;

  - as an instance with the specified _`datasetId`_ if present;

  then an error of type [ResourceNotFound]{.HTML-Error}

- Replace the existing Attribute value instance with the value from the

  Attribute Fragment provided.

  - If the Attribute value to be replaced is represented in the **value only**

    representation, the _`type`_ of any pre-existing Attribute in the target

    entity shall be preserved.

  - If a user _`@context`_ has been supplied, the Attribute Fragment shall

    undergo expansion prior to replacement (see clause 8.2.4)

  - If the Attribute whose value is to be set previously contained an

    _`observedAt`_ sub-Attribute and the value to be replaced is represented in

    the **value only** representation:

    - if an _`observedAt`_ timestamp is defined, then the _`observedAt`_

      sub-Attribute is updated using the timestamp supplied.

    - if no _`observedAt`_ timestamp is defined, then the _`observedAt`_

      sub-Attribute is updated using the timestamp of the [Context

      Broker]{.HTML-Keyboard}

#### 10.2.6.5 Output data

None.

### 10.2.7 Delete Attribute

#### 10.2.7.1 Description