Variant – OPC Unified Architecture

H.8 Variant

For the ReversibleEncoding, Variant values shall be encoded as a JSON object with the fields shown in Table H.7.

Table H.7 – JSON Object Definition for a Variant

Name	Description
Type	The built-in type for the value contained in the Body (see Table 1) encoded as JSON number. If type is 0 (NULL) the Variant contains a NULL value and the containing JSON object shall be omitted or replaced by the JSON literal ‘null’ (when an element of a JSON array).
Body	If the value is a scalar, it is encoded using the rules for type specified for the Type. If the value is a one-dimensional array it is encoded as JSON array (see H.9). Multi-dimensional arrays are encoded as a one-dimensional JSON array which is reconstructed using the value of the Dimensions field (see 5.2.2.16).
Dimensions	The dimensions of the array encoded as a JSON array of JSON numbers. The Dimensions are omitted for scalar and one-dimensional array values.

Name

Description

Type

The built-in type for the value contained in the Body (see Table 1) encoded as JSON number.

If type is 0 (NULL) the Variant contains a NULL value and the containing JSON object shall be omitted or replaced by the JSON literal ‘null’ (when an element of a JSON array).

Body

If the value is a scalar, it is encoded using the rules for type specified for the Type.

If the value is a one-dimensional array it is encoded as JSON array (see H.9).

Multi-dimensional arrays are encoded as a one-dimensional JSON array which is reconstructed using the value of the Dimensions field (see 5.2.2.16).

Dimensions

The dimensions of the array encoded as a JSON array of JSON numbers.

The Dimensions are omitted for scalar and one-dimensional array values.

For the NonReversibleEncoding, Variant values shall be encoded as a JSON value containing only the value of the Body field. The Type and Dimensions fields are dropped. Multi-dimensional arrays are encoded as a multi-dimensional JSON array as described in H.9.

Decoders that support the NonReversibleEncoding need to have out of band knowledge of value encoded in the Variant or treat the value as a generic JSON object.