[Cif2-encoding] Drafting issues

[James Hester]

I have included below revised text, this time in plain text format in
case 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 that
UTF8 is the 'preferred' encoding of CIF2 rather than the 'designated'
encoding.  This is in keeping with the newfound status of UTF16 as an
acceptable encoding
(2) In Change 1, I've slightly altered the text on encoding
disambiguation that Herbert and I added and changed the commentary on
BOM for clarity
(3) From the 3rd sentence to the end of the first paragraph of CHANGE
2, I have incorporated the paragraph that Herbert and I worked on, and
largely removed the preceding paragraph of Herbert's motion.  The
removal of the preceding paragraph is an attempt to avoid confusion
and because it was largely discussion, rather than specification.  You
will also note some small changes to Herbert's and my text, which I
hope is acceptable under the rubric of cleanup.  I've also added a
clarificatory comment about UTF8 and UTF16.
In general this paragraph is quite scrappy and I believe could be
better focussed.  In particular, does anybody have an objection to
UTF8 and UTF16 being the only acceptable CIF2 encodings where
non-ASCII codepoints are present and in the absence of a
disambiguation signature?  If we accept this, then we can chop out the
algorithmic determination part (which is really just a statement of
principle, and by itself not something that you can write a program
based on).
(4) I have changed 'text' in the first line of that same paragraph to
read 'plain text'.  I hope this is acceptable as a proxy for a more
long-winded definition.  If it is not, then we need to add a full
definition of 'text' to the definitions section, and I believe that
there are several floating around that are acceptable to everybody.

If anybody has an objection to these changes, please identify the
change, state your objection *precisely*, and give an alternative that
would be satisfactory to you.

James.

==========================================================================
CIF - Changes to the specification
01 October  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
preferred 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.  The immediately following space
on this line is reserved for encoding disambiguation signatures.  Note
that where a Unicode BOM is used, it would appear prior to the magic
code 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 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. For compatibility with CIF1 behaviour,
there is no formal restriction on the encoding of CIF2 files providing
they contain only code points from the ASCII range.  If a CIF2 file
contains characters equivalent to Unicode code points greater than
U+0077 (127 decimal), then the particular encoding used must either be
UTF8 or algorithmically identifiable from the CIF2 file itself. Note
that UTF16 with a BOM conforms to this requirement.  The use of a BOM
for unicode encodings, including UTF8, is recommended.  Acceptable
identification algorithms will be published as necessary as annexes to
this standard (see description of magic code and encoding
disambiguation in Change 1).  In the absence of an encoding
disambiguation signature, it is safe to assume that the encoding of a
CIF2 file containing characters outside the ASCII range is either UTF8
or UTF16.
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.

On Fri, Oct 1, 2010 at 2:44 PM, James Hester <jamesrhester at 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 at 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 9907
F +61 (02) 9717 3145
M +61 (04) 0249 4148