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Re: [ddlm-group] Role of separators in CIF
- To: Group finalising DDLm and associated dictionaries <[email protected]>
- Subject: Re: [ddlm-group] Role of separators in CIF
- From: Nick Spadaccini <[email protected]>
- Date: Wed, 02 Dec 2009 20:47:33 +0800
- Authentication-Results: postfix;
- In-Reply-To: <[email protected]>
msg00038 correctly states that the restriction of the character set for
non-delimited strings is non-negotiable if we are to adopt the features of
DDLm. That is a restriction the syntax has to be in place for delimited
lists and tables to be possible.
At the time (some two messages prior) the restriction I proposed was
everything except for alphnumeric ascii and a few punctuation characters
(because it was tightly aligned to the restrictions on characters for
datanames). By the time that thread gets to msg00099 the restriction is only
a few punctuation characters. Clearly people understood the
non-negotiability had to do with the requirement of a restriction, but that
the character set was negotiable - otherwise the 61 messages between
msg00038 and msg00099 shouldn't have been possible.
The restriction I proposed in msg00099 was all the terminator characters
plus the token separators for lists and tables (those at that time, they
have since evolved). The use of terminators in non-delimited strings can
cause problems, especially when viewed or they are ambiguous. Can I
construct lexing rules such that " and ' can be included in a non-delimited
string so that is not be ambiguous or result in error - like Simon I suspect
yes, I haven't thought of an example that systematically fails.
Do I think it is sensible to restrict the terminator characters and
separators except for two? No. I think a consistent rule that terminators
and separators are All disallowed makes more sense and easier to articulate.
For example the two cases below would be non-delimited strings.
_quote ."Hello"
_quote ``Hello''
However it would seem only JW and I have this point of view. So cast your
final votes and lets get on with it. I think this will finish finally the
syntactic issues.
For the record (I think) the restriction I propose would be
" ' : { } [ ] # commas are now returned to the allowed list
Or if you vote "for", the restriction is
: { } [ ]
Nick
On 1/12/09 6:55 PM, "Brian McMahon" <[email protected]> wrote:
> I want to vote "For" on this proposition, but I'm concerned by Nick's
> assertion of 9 October
> http://www.iucr.org/__data/iucr/lists/ddlm-group/msg00038.html
>
> (1) restricting the character set of non-delimited strings is
> NON-NEGOTIABLE. If we don't restrict it, then we can't build
> recursive data structures and exploit DDLm.
>
> I understood this to be definitely ruling out the embedding of the
> quote characters in non-delimited strings, but I've lost track of the
> details of the subsequent discussions.
>
> Regards
> Brian
>
> On Tue, Dec 01, 2009 at 04:56:52PM +1100, James Hester wrote:
>> *NOTE REQUEST FOR VOTE BELOW*
>>
>> Simon: From reading your previous emails, I'm guessing that the source of
>> your concern is that the possible characterset of non-delimited strings
>> appears more restrictive than is strictly necessary. In particular, you're
>> not sure why we have excluded quote and double quote from non-delimited
>> strings.
>>
>> You are correct that the other CIF2 syntax does not require that quote or
>> double quote are excluded from non-delimited strings (apart from the first
>> character, of course). The exclusion of the quote/double quote was on
>> general principle of keeping all characters that serve as delimiters out of
>> non-delimited strings, even if those characters could never cause confusion.
>> It also has the benefit of allowing some syntax errors to be picked up.
>>
>> Nick is with me in Sydney, and we have decided that this is the sort of
>> issue that we just have to vote on, as the arguments either way are not
>> conclusive.
>>
>> I would therefore call everybody to vote on the following proposition:
>>
>> "That <quote> and <double quote> may appear in non-delimited strings, as
>> long as they are not the first character"
>>
>> Voting so far:
>>
>> Against: Nick
>> For: James
>> Agnostic: ?
>>
>> --
>> T +61 (02) 9717 9907
>> F +61 (02) 9717 3145
>> M +61 (04) 0249 4148
> _______________________________________________
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cheers
Nick
--------------------------------
Associate Professor N. Spadaccini, PhD
School of Computer Science & Software Engineering
The University of Western Australia t: +61 (0)8 6488 3452
35 Stirling Highway f: +61 (0)8 6488 1089
CRAWLEY, Perth, WA 6009 AUSTRALIA w3: www.csse.uwa.edu.au/~nick
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