public String getServiceArnNamespace(ToShapeId serviceId) {
        return arnServices.containsKey(serviceId.toShapeId())
                ? arnServices.get(serviceId.toShapeId())
                : serviceId.toShapeId().getName().toLowerCase(Locale.US);
    }
Gets the ARN service namespace of a service shape.

@param serviceId Service shape to get ARN namespace of.
@return Returns the resolved ARN service namespace, defaulting to the
  lowercase shape name if not known.
smithy-aws-traits/src/main/java/software/amazon/smithy/aws/traits/ArnIndex.java