Limit the number of characters with string datatype

[jdacoello]

Discussed in https://github.com/COVESA/vehicle_signal_specification/discussions/533

^{Originally posted by jdacoello February 10, 2023} Is it possible to define the number of valid characters when using string datatype? One example would be to set light colours using hexadecimal color code, where 7 characters are expected.

• #ABCDEF

If not, I can create an issue to work on that.

Another example where this function can help is the VIN number:

VehicleIdentification.VIN:
  datatype: string
  type: attribute
  description: 17-character Vehicle Identification Number (VIN) as defined by ISO 3779.

In practice, how do you enforce the use of 17 characters? If this characteristic is only mentioned in the description, one must have a custom function that does the job. In contrast, if a field in VSS explains the constraints, the user can refer to the described constraints.

[erikbosch]

There is no mechanism for that today. We have a similar topic for strings where the description says it shall be time formatted according to ISO 8601. One thought I had at a time was to "invent" special units, like unit: VIN , unit: color and describe the expected formatting as a comment in the unit file. Then one could even possibly add a regexp to the unit definition file which tooling/servers/client possibly could use for validation.

[jdacoello]

There is no mechanism for that today. We have a similar topic for strings where the description says it shall be time formatted according to ISO 8601. One thought I had at a time was to "invent" special units, like unit: VIN , unit: color and describe the expected formatting as a comment in the unit file. Then one could even possibly add a regexp to the unit definition file which tooling/servers/client possibly could use for validation.

I would not use the unit for something that is not a unit. However, the approach taken for handling units could be reused with a new field. So, instead of defining that as a unit, we can do it as format (or some similar keyword).

[erikbosch]

I came up with a possible but maybe somewhat ugly idea for the string datatype. We have already min and max attributes, we typically use them today just for int/float values. We could possibly give them a different semantic meaning for signals of type string and string[] and let them indicate min/max length for the string (excluding trailing null).