[sc34wg3] TM Data Model issue: assoc-role-player-type

[Geir Ove Grønmo]

Another issue: I see that the properties [type] and [role playing
topic] have now been made optional on the association role item. 

I have a suspicion that the rationale for this decision is that one
should be able to represent non-complete data. Unfortunately this
decision has some rather nasty side effects. Two words: duplicate
suppression. 

The current equality rules consider properties with the value null to
be identical. This means that any association role items that have a
null value in their [type] or [role playing topic] properties may get
suppressed because some other item also has the null
value. Furthermore it may also lead to associations being suppressed.

This effectively means that what is considered by the author to be
"not complete" is being considered "suppressable" by the topic map
processor.

If authors want to represent non-complete data one cannot do this
using the current null value. The NULL specified in the current TMDM
draft is not the same as a NULL in SQL, i.e. it _not_ mean "unknown".

I know that the XTM syntax allows the two values to be left out, but I
would much rather like to see this "bug" be fixed than for it to make
its way into the Topic Map Data Model.

My view on this is that one should be draconian on this issue and
require both properties. How can it hurt? I think it'll hurt people
more by letting this change through.

Geir O.