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Creating the attributes and values

Then let us create the attributes and values needed. We need something to call the attribute which describes whether a vehicle runs on rail or road. It is often not easy to come up with a name. We shall use travelsOn for the attribute and TravelMediumType for the rail, road etc. (We might extend this to air at the same time with little effort.)

Add to the file immediately after the asserted hierarchy a new attribute definition, a new value type, and the appropriate sanctions:

DomainAttribute newAttribute travelsOn isTraveledOnBy allAll manyOne.
SymbolicValueType newSub TravelMediumType
  TravelMediumType newSub air.
  TravelMediumType newSub rail.
  TravelMediumType newSub road.
Vehicle grammaticallyAndSensibly travelsOn TravelMediumType.

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