[wfc] CHECKSUM Proposal

[William Pence]

Eric Greisen wrote:
> 
> The FITS community also needs to look at another issue - whether all
> of the "conventions", even those that are widespread, ought to be
> "standards".  If something is a standard, then most widespread
> software systems ought to support it.  If it is a convention, we have
> a greater leeway.

Conventions that are widely used and that provide a significant capability
to FITS need to be added to the standard to preserve and document them for
other users.  If this isn't done then there is a danger that the precise
details of the convention will be forgotten or misinterpreted by others,  or
that other duplicate conventions will be invented and used by people who are
unaware of the other existing convention.  

Don Wells wrote:
>
> However the current form of the proposal contains only the
> technical details, and so it won't help me in the process of
> persuading the archive people to implement CHECKSUM.  In this respect
> the 1995 Seaman and Pence paper was better. Does the proposal
> presented to the WFC supercede the 1995 paper?  If 'yes', then I
> recommend that the 1995 paper be upgraded so that I can use it.

The current proposal is a more concise and reorganized version of the 1995
paper. (It is 7 pages long compared to 21 pages in the 1995 paper). 
Everything in the 1995 paper is still valid.  The only technical difference
is that the current proposal does not explicitly reserve the CHECKVER
keyword for possible future use;  we decided that the need for this keyword
was so uncertain that there was no point in reserving it now.   Essentially
everything in sections 1, 2, 3, and 5, of the 1995 paper has been retained
in the current proposal.  Only section 4 of the 1995 paper has been omitted,
which briefly discusses a variety of other checksum schemes such as CRCs,
message digests, digital signatures, and error correction algorithms.   This
section was removed from the current proposal mainly because the discussion
of alternate schemes is somewhat of a digression and is not strictly
relevant to the CHECKSUM proposal itself, and it seemed inappropriate to ask
the FITS committees to vote on this 'off-topic' section.

-Bill Pence
-- 
____________________________________________________________________
Dr. William Pence                          pence at tetra.gsfc.nasa.gov
NASA/GSFC Code 662         HEASARC         +1-301-286-4599 (voice)     
Greenbelt MD 20771                         +1-301-286-1684 (fax)