Value Restrictions

Specifying allowed values

Optionally it is possible to define an array of allowed values, which will restrict the usage of the data entry in the implementation of the specification. It is expected, that any value not mentioned in the array is considered an error and the implementation of the specification shall react accordingly. The datatype of the array elements is the datatype defined for the data entry itself. For attributes it is possible to optionally set a default value.

  datatype: string
  type: attribute
  default: 'FRONT_LEFT'
  allowed: ['FRONT_LEFT', 'FRONT_RIGHT']
  description: Position of the steering wheel on the left or right side of the vehicle.

If allowed is set, min or max cannot be defined.

The allowed element is an array of values, all of which must be specified in a list. Only values can be assigned to the data entry, which are specified in this list.

The datatype specifier gives the datatype of the individual elements of the allowed list. In general allowed: is valid for all datatypes, including integer- and float-based datatypes, unless otherwise specified.

Recommendation on String values

String values used for default and allowed statements may contain characters from the printable subset of the Unicode character set. If using COVESA VSS-tools it is recommended to use single quotes (') around values as tooling otherwise might handle literals like OFF as boolean values with unexpected result. It is recommended not to specify a dedicated value corresponding to “unknown” or “undefined” unless there is a relevant use-case for that particular signal. The background is that a signal with an array of allowed values shall be handled just as any other signal. If e.g. the value of current speed or vehicle weight is unknown, then the vehicle shall not publish the corresponding signal. Similarly, for the example above, if the steering wheel position is unknown then SteeringWheel.Position shall not be published.

Allowed values for array datatypes

The allowed keyword can also be used for signals of array datatype. In that case, allowed specifies the only valid values for array elements. The actual value of the signal is expected to contain a subset of the values specified in allowed.


  datatype: string[]
  type: attribute
  description: Brief list of dog breeds.

Examples of valid arrays:

  [] # Empty array
  ['PUG', 'PUG'] # duplication is allowed

Example of an invalid array:

  ['PAPILLON', 'VIZSLA', 'LOBSTER'] # LOBSTER is not in the allowed value list

Allowed for struct datatypes

Please see struct documentation.