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Re: [ddlm-group] Role of separators in CIF
- To: Group finalising DDLm and associated dictionaries <ddlm-group@iucr.org>
- Subject: Re: [ddlm-group] Role of separators in CIF
- From: Nick Spadaccini <nick@csse.uwa.edu.au>
- Date: Wed, 02 Dec 2009 20:47:33 +0800
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- In-Reply-To: <20091201105503.GE20378@emerald.iucr.org>
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" <bm@iucr.org> 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 > _______________________________________________ > ddlm-group mailing list > ddlm-group@iucr.org > http://scripts.iucr.org/mailman/listinfo/ddlm-group 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 MBDP M002 CRICOS Provider Code: 00126G e: Nick.Spadaccini@uwa.edu.au _______________________________________________ ddlm-group mailing list ddlm-group@iucr.org http://scripts.iucr.org/mailman/listinfo/ddlm-group
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