[fitsbits] reopening of Public Comment Period on the CONTINUE convention

[Demitri Muna]

Hi Peter,

On Mar 9, 2016, at 4:13 AM, Peter Weilbacher <pweilbacher at aip.de> wrote:

>> There is a standard here that is used in virtually every (every)
>> computer language - continuation or concatenation characters are
>> located outside of the string being quoted.
> 
> But we are not discussing a computer language here, but a file format.

I mentioned it as the convention will already be familiar to people. But whether it’s a file format or a computer language is irrelevant; the question what is easier to parse and/or read, first by a human and second by a computer. When one sees a line end with an ampersand and a single quote, the current proposal says “this might be a continuation character, or it might not.” When virtually every computer language agrees on a certain syntax, it’s worth paying attention to. Can anyone point to a counterexample where the continuation character is contained within a quoted string anywhere?

> I don't think that the FITS Standard allows to have anything between the
> value and the '/' that starts the comment. At least that's how I
> understand Section 4.1.1 and Appendix A. So having the continue
> character outside the string literals would make a very fundamental
> change to the FITS format. And quite hard on every FITS header parser.

The current proposal specifically modifies Section 4.1.1, so that is what is under discussion. Given this:

STRKEY = 'This keyword value is continued&'
CONTINUE ' over multiple keyword records.'

or this:

STRKEY = 'This keyword value is continued' &
CONTINUE ' over multiple keyword records.'

an existing parser would treat the ampersand as part of the value and see no comment. I don’t see how this is a fundamental change or how it will break existing parsers. Can you provide an example where this would be a problem? You would never have this, for example:

STRKEY  = 'string' & / comment

This seems to be the edge case, where again the ampersand is not between the '/' and the comment, which is still not a problem:

STRKEY  = 'some string that ends here but is followed by a comment' &
CONTINUE '' / comment here 

>> If the motivation is to turn into a standard something that someone
>> else decided ad hoc to do, then I’d ask if this really is the best way
>> to define standards? The fact that one institute did something doesn’t
>> necessarily make it the best idea, and in this case I really don’t
>> think it is.
> 
> The discussions about the CONTINUE discussion predate my time in
> astronomy as well, but if you read up on the convention's history, you
> will find quite a few messages to this list from 1993 and 94. So it was
> not decided "ad-hoc" at all, and not by one institute, either. (I think
> this is true for all the conventions that currently exist.)

The oldest message on the web archive only goes back to March 1996 (which I note with amusement contains a message with the subject "[ANN] New FITS viewer for the Macintosh"). I mean ad hoc in the sense that it wasn't part of the format. But I think the argument that it was discussed a quarter century ago isn't a strong one; I am pointing out very specific reasons why this is not the best idea.

> I agree that this is not the most beautiful way to create FITS headers.
> But since the motivation here is rather to have an incremental
> improvement that works (we know, because it has seen usage for 20+
> years) instead of reinventing the FITS format, I agree with the
> proposal.


I think this is a very important point. There has been a lot of discussion about file formats and pretty wide dissatisfaction with FITS. There's no question it's showing its age. I think it would be one thing if there was a commitment to properly addressing the real concerns with a proper FITS v2.0 versus incremental patching. The past should guide the future, not constrain it.

Cheers,
Demitri

_________________________________________
Demitri Muna
http://muna.com

Department of Astronomy
Le Ohio State University

My Projects:
http://nightlightapp.io
http://trillianverse.org
http://scicoder.org



-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listmgr.nrao.edu/pipermail/fitsbits/attachments/20160310/7db66180/attachment-0001.html>