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Re: [Cif2-encoding] Drafting issues

I have included below revised text, this time in plain text format incase the HTML format of the previous email was a problem.
I have made the following changes:
(1) In first paragraph of the TERMINOLOGY section I have written thatUTF8 is the 'preferred' encoding of CIF2 rather than the 'designated'encoding.  This is in keeping with the newfound status of UTF16 as anacceptable encoding(2) In Change 1, I've slightly altered the text on encodingdisambiguation that Herbert and I added and changed the commentary onBOM for clarity(3) From the 3rd sentence to the end of the first paragraph of CHANGE2, I have incorporated the paragraph that Herbert and I worked on, andlargely removed the preceding paragraph of Herbert's motion.  Theremoval of the preceding paragraph is an attempt to avoid confusionand because it was largely discussion, rather than specification.  Youwill also note some small changes to Herbert's and my text, which Ihope is acceptable under the rubric of cleanup.  I've also added aclarificatory comment about UTF8 and UTF16.In general this paragraph is quite scrappy and I believe could bebetter focussed.  In particular, does anybody have an objection toUTF8 and UTF16 being the only acceptable CIF2 encodings wherenon-ASCII codepoints are present and in the absence of adisambiguation signature?  If we accept this, then we can chop out thealgorithmic determination part (which is really just a statement ofprinciple, and by itself not something that you can write a programbased on).(4) I have changed 'text' in the first line of that same paragraph toread 'plain text'.  I hope this is acceptable as a proxy for a morelong-winded definition.  If it is not, then we need to add a fulldefinition of 'text' to the definitions section, and I believe thatthere are several floating around that are acceptable to everybody.
If anybody has an objection to these changes, please identify thechange, state your objection *precisely*, and give an alternative thatwould be satisfactory to you.
James.
==========================================================================CIF - Changes to the specification01 October  2010This document specifies changes to the syntax of CIF. We refer to thecurrent syntax specification of CIF as CIF1, and the new specificationas CIF2. To date all archival CIFs are CIF1.The changes to syntax are necessitated by the adoption of newdictionary functionalities that introduce several extensions,including new data types, and method definitions using dREL.It is assumed the reader has a thorough understanding of the CIF1 specification.TERMINOLOGYReference to character(s) means abstract characters assigned codepoints by Unicode.  Specific characters are referenced according toUnicode convention, U⁠+⁠xxxx[x[x]], where xxxx[x[x]] is the four- tosix-digit hexadecimal representation of the assigned code point. Thepreferred character encoding for CIF2 is UTF-8.Reference to ASCII characters means characters U⁠+⁠0000 throughU⁠+⁠007F, or, equivalently the first 128 characters of the ISO‑8859‑1(LATIN‑1) character set.Reference to newline or \n means the sequence that conventionallyterminates a line record (which is environment dependent).  See Change3.Reference to whitespace means the characters ASCII space (U⁠+⁠0020),ASCII horizontal tab (U⁠+⁠0009) and the newline characters. Withoutregard to local convention, the various other characters that Unicodeclassifies as whitespace (character categories Zs and Zp) do notconstitute whitespace for the purposes of CIF2.PREAMBLECIF2 significantly extends CIF1 functionality, primarily through newdictionary features. CIF2 is not fully backwards-compatible with CIF1:many files compliant with CIF1 are also compliant with CIF2, but someare not (see especially change 5, below).  The CIF1 standard willcontinue to operate for the foreseeable future in parallel with CIF2.CHANGE 1 ‒ NEW (MAGIC CODE)A CIF2 file is uniquely identified by a required magic code at thebeginning of its first line. The code is,#\#CIF_2.0followed immediately by whitespace.  The immediately following spaceon this line is reserved for encoding disambiguation signatures.  Notethat where a Unicode BOM is used, it would appear prior to the magiccode in the byte stream and does not form part of the CIF text.CHANGE 2 ‒ NEW (CHARACTER SET)CIF2 files are standard variable length plain text files, which forcompatibility with older processing systems will have a maximum linelength of 2048 characters. As discussed above and below, however,there are some restrictions on the character set for token delimiters,separators and data names. For compatibility with CIF1 behaviour,there is no formal restriction on the encoding of CIF2 files providingthey contain only code points from the ASCII range.  If a CIF2 filecontains characters equivalent to Unicode code points greater thanU+0077 (127 decimal), then the particular encoding used must either beUTF8 or algorithmically identifiable from the CIF2 file itself. Notethat UTF16 with a BOM conforms to this requirement.  The use of a BOMfor unicode encodings, including UTF8, is recommended.  Acceptableidentification algorithms will be published as necessary as annexes tothis standard (see description of magic code and encodingdisambiguation in Change 1).  In the absence of an encodingdisambiguation signature, it is safe to assume that the encoding of aCIF2 file containing characters outside the ASCII range is either UTF8or UTF16.In keeping with XML restrictions we allow the charactersU⁠+⁠0009 U⁠+⁠000A U⁠+⁠000DU⁠+⁠0020 – U+007EU+00A0 - U⁠+⁠D7FFU⁠+⁠E000 – U+FDCFU⁠+⁠FDF0 - U+FFFDU⁠+⁠10000 - U⁠+⁠10FFFDIn addition, character U+FEFF and characters U+xFFFE or U+xFFFF wherex is any hexadecimal digit are disallowed. Unicode reserves the codepoints E000 – F8FF for private use. The IUCr and only the IUCr mayspecify what characters are assigned to these code points in thecontext of CIF2.Reasoning: There is growing demand for the wider character setafforded by Unicode to be made available in applications, especiallythose where internationalisation is an issue.
On Fri, Oct 1, 2010 at 2:44 PM, James Hester <jamesrhester@gmail.com> wrote:>> Before I post my revised text, I have only just realised (upon close perusal of the two texts) that Herbert's motion is substantially the same as the 'Changes' document, just without the headings etc, so we are discussing almost the same document.  My apologies for the confusion.>> James.>> On Fri, Oct 1, 2010 at 2:37 PM, James Hester <jamesrhester@gmail.com> wrote:>>>> Dear Group,>>>> As I think we have reached a consensus in principle, and are now moving into discussion of precise definitions, let us have wording arguments only once (that is, for a single document).  I think that our base document must be the one that the DDLm group agreed on - the link once again is http://www.iucr.org/__data/assets/pdf_file/0017/41426/cif2_syntax_changes_jrh20100705.pdf - simply because it will be unnecessarily confusing for the DDLm group to deal with two documents at once, and the 'Changes' document is admirably precise.  I reiterate once again that I am happy with the motion that Herbert presented, with the proviso that one paragraph is rewritten as I have recently proposed.  Herbert - if you would like to negotiate that paragraph with me by Skype, I'm happy to do that too.>>>> I have appended a text version of what I consider to be the relevant sections of the 'changes' document to this message.  I am happy to provide the complete document in OpenOffice format to anybody who would like it.  Herbert - if you think any of the non-encoding discussion in your motion is not already covered in the 'Changes' document, please advise.>>>> I will be posting my own suggestion, largely based on parts of the motion that Herbert and I drafted yesterday, in a reply to this email.>>>> CIF - Changes to the specification>>>> 05 July 2010>>>> This document specifies changes to the syntax of CIF. We refer to the current syntax specification of CIF as CIF1, and the new specification as CIF2. To date all archival CIFs are CIF1.>>>> The changes to syntax are necessitated by the adoption of new dictionary functionalities that introduce several extensions, including new data types, and method definitions using dREL.>>>> It is assumed the reader has a thorough understanding of the CIF1 specification.>>>> TERMINOLOGY>>>> Reference to character(s) means abstract characters assigned code points by Unicode. Specific characters are referenced according to Unicode convention, U⁠+⁠xxxx[x[x]], where xxxx[x[x]] is the four- to six-digit hexadecimal representation of the assigned code point. The designated character encoding for CIF2 is UTF-8.>>>> Reference to ASCII characters means characters U⁠+⁠0000 through U⁠+⁠007F, or, equivalently the first 128 characters of the ISO 8859 1 (LATIN 1) character set.>>>> Reference to newline or \n means the sequence that conventionally terminates a line record (which is environment dependent). See Change 3.>>>> Reference to whitespace means the characters ASCII space (U⁠+⁠0020), ASCII horizontal tab (U⁠+⁠0009) and the newline characters. Without regard to local convention, the various other characters that Unicode classifies as whitespace (character categories Zs and Zp) do not constitute whitespace for the purposes of CIF2.>>>> PREAMBLE>>>> CIF2 significantly extends CIF1 functionality, primarily through new dictionary features. CIF2 is not fully backwards-compatible with CIF1: many files compliant with CIF1 are also compliant with CIF2, but some are not (see especially change 5, below). The CIF1 standard will continue to operate for the foreseeable future in parallel with CIF2.>>>> CHANGE 1 ‒ NEW (MAGIC CODE)>>>> A CIF2 file is uniquely identified by a required magic code at the beginning of its first line. The code is,>>>> #\#CIF_2.0>>>> followed immediately by whitespace.>>>> CHANGE 2 ‒ NEW (CHARACTER SET)>>>> CIF2 files are standard variable length text files, which for compatibility with older processing systems will have a maximum line length of 2048 characters. As discussed above and below, however, there are some restrictions on the character set for token delimiters, separators and data names.>>>> In keeping with XML restrictions we allow the characters>>>> U⁠+⁠0009 U⁠+⁠000A U⁠+⁠000D>> U⁠+⁠0020 – U+007E>> U+00A0 - U⁠+⁠D7FF>> U⁠+⁠E000 – U+FDCF>> U⁠+⁠FDF0 - U+FFFD>> U⁠+⁠10000 - U⁠+⁠10FFFD>>>> In addition, character U+FEFF and characters U+xFFFE or U+xFFFF where x is any hexadecimal digit are disallowed. Unicode reserves the code points E000 – F8FF for private use. The IUCr and only the IUCr may specify what characters are assigned to these code points in the context of CIF2.>>>> Reasoning: There is growing demand for the wider character set afforded by Unicode to be made available in applications, especially those where internationalisation is an issue.>>>> -->> T +61 (02) 9717 9907>> F +61 (02) 9717 3145>> M +61 (04) 0249 4148>>>> --> T +61 (02) 9717 9907> F +61 (02) 9717 3145> M +61 (04) 0249 4148


--T +61 (02) 9717 9907F +61 (02) 9717 3145M +61 (04) 0249 4148_______________________________________________cif2-encoding mailing listcif2-encoding@iucr.orghttp://scripts.iucr.org/mailman/listinfo/cif2-encoding

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