Datatypes R2 Issue 20
Data Types Issue 20: Cardinality of IVL<T>
Introduction
The cardinality of a Set is the number of items in the set. While it's not clear exactly what this might mean with a SET<REAL> or SET<TS>, it's clear what it means for SET<INT>, SET<AD>, etc.
IVL is a specialisation of a set. So an interval of 3..5 is a Set of 3,4,5. Therefore the cardinality of the interval 3..5 is 3. And the cardinality of an unspecified interval is unknown.
However in the Static Models, the cardinality of interval is marked as 0..1.
? backward compatible.
Discussion
So, something is wrong here. The cardinality value for interval should be 0..* everywhere, rather than 0..1.
An alternative view is that IVL is not a specialisation of SET ;-)
This problem would be overtaken by the proposal from Lloyd and Grahame to change the way cardinality is assigned to attributes.
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