I Even aside from the "exponential" notation, these features aren't the same. ISO 8601 says years with more than four digits must be agreed on by the parties, and it strongly implies that an exact _number_ of additional digits must be agreed on. (Which makes sense in that otherwise a string like "+1919" might mean the year 1919 or the century beginning in 191901. I think.) In EDTF, years with more than four digits can always be used, and there's no need for (or point to!) agreement between the parties. So EDTF's representation is more standardized and well-defined -- and much better, IMO.
On May 7, 2015, at 1:14 AM, Nathan Harrenstein <[log in to unmask]> wrote:
> I was reading the ISO 8601:2004(E) standard and noticed that there is already a feature for representing long years, called "expanded representations" (§18.104.22.168). Reading through the EDTF listserv archives, I got the impression that this feature was not known at the time long years were ideated.
> "By mutual agreement of the partners in information interchange, it is permitted to expand the component
> identifying the calendar year, which is otherwise limited to four digits. This enables reference to dates and times in calendar years outside the range supported by complete representations, i.e. before the start of the year  or after the end of the year " (§3.5).
> To specify an "expanded representation", the year is prefixed by a "+" or "-". It doesn't cover the scientific notation features, however.
> Am I missing something or are these features the same?
Woodrow Wilson Indiana Teaching Fellow
Adjunct Associate Professor of Informatics
Visiting Scientist, Research Technologies
Indiana University Bloomington