Abstract base class for a coordinate reference system

abstract class CoordinateReferenceSystem {
 /**
  * The standardized identifier for this reference system.
  *
  * A coordinate references system can be assigned more than
  * one idetifier, see also [aliases]
  */
 String get code;

 /**
  * A list of code aliases for this reference system.
  *
  * The empty list, if no alternative codes are known for this
  * coordinate reference system.
  */
 List<String> get aliases;
}