SCHEMA test_derived_attribute;

ENTITY point;
END_ENTITY;

ENTITY vector;
END_ENTITY;

ENTITY circle;
  centre : point;
  radius : REAL;
  axis : vector;
DERIVE
  area : REAL := PI*radius**2;
  perimeter : REAL := 2.0*PI*radius;

END_ENTITY;
END_SCHEMA;
