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Re: [ddlm-group] THREAD 3: The alphabet of non-delimited strings.

I won't commit to any of this until I have gone back a read the last 2 weeks
of exchanges between you and Herb. I am ensconced at the PDB doing a number
of different things and haven't looked at the emails on this discussion list
since arriving here.

I think we have a very serious divergence between what we can do in DDLm
versus what will be done (the latter will be very little change relative to
the existing cif X.Y standards). However, your solution may prove to be the
only pragmatic way forward for the IUCr.

My solution is to build the parsers for STAR that will fully support DDLm in
the way it has to. This is definitely the way forward for STAR since there
is a lot of power in what can be done, but it is hindered by legacy
considerations for CIF (which by the way have no bearing on STAR).

What ever works for CIF will have to essentially be a hack to accommodate
certain historical restrictions. I can't see any easy way around this.



On 6/10/09 11:01 PM, "James Hester" <jamesrhester@gmail.com> wrote:

> Dear All:
> 
> As a result of the discussion with Herbert I can see two differing
> approaches to these CIF syntax changes:
> 
> 1. Any changes to CIF syntax should be such that earlier syntax
> versions form a subset of the new syntax, i.e. files in the older
> syntax will also conform to the new syntax
> 
> or
> 
> 2. When making changes to the standard, the opportunity should be
> taken to simplify and streamline syntax as much as possible.
> 
> Advantages of (1): a single CIF parser can be maintained for all
> syntax versions; a CIF writer is always conformant to the latest
> version and only needs changing if new syntax features are to be used;
> the existing CIF software ecosystem is minimally affected
> 
> Advantages of (2): implementation of CIF readers/writers from scratch
> is easier; the standard is easier to define formally and more
> aesthetically pleasing; mistakes in previous versions can be fixed,
> warts do not accumulate
> 
> I would like to suggest we act as follows: in essence, we deprecate
> rather than exclude.  In detail:
> 
> 1. For this edition of the standard (1.2) we follow Herbert's line,
> leaving everything currently defined untouched.  We simply add triple
> quote delimited strings and bracket expressions.  The content of
> non-delimited strings in bracket expressions will be as proposed by
> Nick.
> 
> 2. In the documents associated with the new standard we strongly
> suggest that all non-delimited strings use the same character set as
> for non-delimited strings in bracket expressions (i.e. Nick's original
> proposal).  We might point out that this simplifies code for writing
> CIFs, and perhaps (if all agree) we add that using the CIF1.1
> non-delimited string character set is deprecated, darkly foreshadowing
> that a future version of the syntax standard will adopt this character
> set for all non-delimited strings.
> 
> 3. We also deprecate including string delimiters inside strings,
> regardless of whitespace issues.
> 
> 4. In all dictionaries we adopt the restricted character set for
> non-delimited strings and exclusion of string delimiters in strings.
> 
> 5. We ask that CheckCIF emit a warning about use of deprecated
> characters in non-delimited strings
> 
> 6. When (say in 10 years' time) a sufficiently large proportion of
> incoming CIFs conform to the new non-delimited string character set,
> we promulgate the 1.3 version of the standard.
> 

cheers

Nick

--------------------------------
Associate Professor N. Spadaccini, PhD
School of Computer Science & Software Engineering

The University of Western Australia    t: +61 (0)8 6488 3452
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e: Nick.Spadaccini@uwa.edu.au





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