Wrong value only submodel-element serialization

[sirchnik]

Description

While comparing with Eclipse Basyx, I noticed that value only serialization deviates from spec in Faaast-service. As '/submodel/submodel-elements/{idShortPath}/$value' should return SubmodelElementValue which defines PropertyValue-serialization as JSON primitives.

Reproduction

Faaast-service: v1.2.0 MongoDB
Basyx 2.0 Milestone 4

submodel creation

```bash curl -X POST \ -H "Content-Type: application/json" \ -d '{ "idShort": "a", "id": "https://admin-hell.io/a", "kind": "Instance", "submodelElements": [ { "idShort": "b", "value": [ { "idShort": "c", "valueType": "xs:long", "value": 0, "modelType": "Property" } ], "modelType": "SubmodelElementCollection" } ], "modelType": "Submodel" }' \ http://localhost:8080/api/v3.0/submodels ```

curl 'http://localhost:8080/api/v3.0/submodels/aHR0cHM6Ly9hZG1pbi1oZWxsLmlvL2E/submodel-elements/b.c/$value?level=core'

Expected

0

Basyx returns "0" as a string which has already reported in their repo.

Output

{
  "c" : 0
}

Additional Context

• I am reporting this issue solely for testing purposes, as I am currently verifying which AAS implementations are functioning. Therefore, I don't need a fix at this time.
• I am also no expert I just wanted to provide feedback.

[mjacoby]

Your observations are correct. However, to be precise, this is not considered a bug since v3.0.x of the specification is underdefined regarding valueOnly serialization stating only the following about valueOnly serialization of properties

But this is only valid for serialization of properties within a submodel. For serialization of properties that are not part of a submodel (as in your example) no definition is given.

This is fixed in the upcoming v3.1 version of the AAS specification (https://admin-shell-io.github.io/aas-specs-antora/IDTA-01001/v3.1/mappings/mappings.html#value-only-serialization-in-json)

The following rules shall be adhered to when serializing a single submodel element with the format "Value":
   Property is serialized as ${Property/value} where ${Property/value} is serialized as described above.

This will be updated in future releases of FA³ST, i.e., FA³ST will also return 0 instead of { "c": 0 } in the future.

[sirchnik]

Okay thanks for the info.
I think this issue can be closed with this.