Sorry I confused some of the terminology and notation. Uncertain and
approximate are ? and ~ and those are all ok, what were dealing with is

So 'u' is said to denote "unspecified" (not "uncertaintly") and I think we
should leave it as such. 

I'm not sure I buy the distinction you are making, that 196x has decade
precision while 196u has year precision, to me they both seem to mean the
same thing.

But I want to move this along as we are near finishing this, and I think we
can maneuver around this.  

So, what I think is best, is 

1. leave 'u' as is, that is, 'u' is a placeholder, with no mention of
precision, as it is now.  

2. Create a new category (in level 2) for 'x' (and remove it from where it
is currently defined, as part of the multiple date category).  Call the new
category "precision by masking", or "masked precision" (suggestions for a
better name welcome) where it is described that 196x means a date within the
years 1960 to 1969, etc.



> -----Original Message-----
> From: Discussion of the Developing Date/Time Standards
> [mailto:[log in to unmask]] On Behalf Of Edward C. Zimmermann
> Sent: Tuesday, August 02, 2011 3:59 PM
> To: [log in to unmask]
> Subject: Re: [DATETIME] Rethinking Precision and "x"
> On Tue, 2 Aug 2011 14:52:46 -0400, Ray Denenberg, Library of Congress
> wrote
> > Ok, I think I have a solution to all of this.
> >
> > 'u' clearly has a much different usage when used internally than when
> > it replaces one or more consecutive rightmost digits. I don't think
> we
> > have
> yet
> > confronted this.
> The semantics for u restricted to application as one or more
> consecutive rightmost digits can have but need not have the semantics
> as a placeholder but does not do well to express measurement precision.
> 199u where u is a placeholder has unknown year but expresses a date
> with a precision of year. 199x by contrast has a precision of decade.
> The u as a rightmost placeholder can be used to express precision via a
> semantics of uncertainty but then it would not be a placeholder..
> This is, I think, a problem with our current specification for u and
> not really x.
> The solution, I think, is to call u a digit placeholder:
> unknown/unconfirmed/untested/unspecified/unmeasured ....
> Its use and semantics are simple. One can use u in place of a digit
> anywhere in a date/time expression.
> >
> > Thus 196u means:
> >     "a date in the 1960s"
> Yes. But with year precision... what year? We reserve the digit place..
> The whole point of u is, I think, the explicit intent "I hope to fill
> in the blanks".
> > and expresses imprecision, where 1u66 might be said to express
> uncertainty.
> I think we should avoid the term "uncertainty" with u and keep to
> placeholder.. Uncertainty to century with year 66 is I think something
> else.. Instead its saying, I think, I know its year 66 and second 1000
> years.. I need to check the century and so I'll leave it as u and come
> back sometime to fill it in.. That I always thought was the reason we
> got them in MARC.. In MARC the u is called "unknown" but its not really
> unknown.. only not available at the moment the record is authored.. Its
> saying "to be filled in later"... Precision is not about filling in
> later.. A sample that weights 2 grams on a balance that reads only to
> gram is a weight of 2 grams with gramm precision.. I might never have
> call to measure it with a more precise balance..
> >
> > In other words I suspect the solution to this problem is not to refer
> > to "rightmost" 'u' as "uncertainly" and instead refer to it as
> "imprecision".
> >
> > And since 'u' means different things when used internally vs.
> > rightmost,
> and
> > perhaps 'u' shouldn't be used for both.
> >
> > I therefore propose that 'x' be used instead of 'u' for level 1
> uncertainty,
> > and that we rename "uncertainly" as "imprecision" for level 1 (and
> > continue to call it 'uncertainty' for level 2 - internal).
> >
> > --Ray
> --
> Edward C. Zimmermann, NONMONOTONIC LAB
> Umsatz-St-ID: DE130492967