Datatypes R2 Issue 65

Introduction

[from Charlie]

There is an error in the abstract datatypes that is not helping us here

 invariant(IVL<T> x) 
      where x.low.isNull.or(x.high.isNull) {
   x.center.notApplicable;
 };

This cannot be true -- since center is used exactly when high and low are unknown (ie null). I think that this should be

 invariant(IVL<T> x)
      where x.low.isNull.xor(x.high.isNull) {
   x.center.notApplicable;
 };

[end]

I think both statements do not belong in the abstract spec. I vote for removing this. (Grahame agreed) Gschadow 22:30, 11 January 2007 (CST)

As a side note: if you truly don't know any of low, high, or center, then you probably do not know the center. However, in some cases you want to say: "I don't know when it started nor when it ended, but I know at time t it was there. What to do about that? Gschadow 22:30, 11 January 2007 (CST) That subject is Datatypes R2 Issue 106. --GrahameGrieve 23:14, 14 June 2007 (CDT)

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