[iaufwg] Appendix A, END keyword

[Andreas Wicenec]

Bill,


On 18.03.2008, at 22:50, William Pence wrote:

> Andreas,
>
> The formal syntax in Appendix A does actually cover the case of the  
> END keyword record.  Formally, the END keyword is a  
> 'FITS_commentary_keyword_record', and more specifically, it is the  
> case where the non-blank keyword field is followed by  
> 'anychar_but_equal'. In other words, since the END keyword record  
> does not have an equal sign in byte 9, it is considered one of the  
> class of commentary keywords.
>
> It is perhaps a little odd to think of the END keyword as a  
> commentary keyword, but this is the most appropriate way to  
> classify it in this formal grammar.  The alternative, which I think  
> is more undesirable, would be to invent a new 3rd major class of  
> keywords just for this one special case (i.e., a new keyword record  
> class that is not a FITS_commentary_keyword_record nor a  
> FITS_value_keyword_record).

I actually got confused by the page break in the middle of the  
definition of the FITS commentary keyword record  definition.
I have nothing against having it as a commentary keyword, but still  
think we could add it just in the same way as the COMMENT and HISTORY,
i.e.

FITS commentary keyword record :=
COMMENT keyword [ascii text char...] |
HISTORY keyword [ascii text char...] |
END keyword [ascii text char...] |
BLANKFIELD keyword [ascii text char...] |
keyword field anychar but equal [ascii text char...] |
keyword field : '=' anychar but space [ascii text char...]

and then further down define the END keyword as

END keyword :=
'E''N''D' space space space space space

This is still not quite correct, because it does not constraint the  
rest of the line to be only spaces, but it is already better than  
leaving it just implicitly defined.

Andreas

>
> This also at least partially explains why the formal grammar is  
> only included as an unofficial appendix to the standard rather than  
> integrating it directly  into Section 4:  most FITS users would  
> likely find this formal grammar rather daunting to parse, so  
> instead, the FITS Standard defines  all the keyword record  
> requirements in plain English.  The wording in section 4 takes  
> precedence over the formal grammar in case of any ambiguities or  
> discrepancies.
>
> Bill
>
> Andreas Wicenec wrote:
>> - Appendix A does not define the END keyword record...
>> As said already, I think the document is in pretty good shape   
>> already, and what I've written are just suggestions. I would agree  
>> to  release the document also
>> without the changes, except the omission of the definition of the  
>> END  keyword record in appendix A.
> -- 
> ____________________________________________________________________
> Dr. William Pence                       William.Pence at nasa.gov
> NASA/GSFC Code 662       HEASARC        +1-301-286-4599 (voice)
> Greenbelt MD 20771                      +1-301-286-1684 (fax)
>
>