- From: Eric Prud'hommeaux <eric@w3.org>
- Date: Wed, 10 Apr 2013 16:46:31 -0400
- To: Peter Patel-Schneider <pfpschneider@gmail.com>
- Cc: W3C RDF WG <public-rdf-wg@w3.org>
* Peter Patel-Schneider <pfpschneider@gmail.com> [2013-04-10 13:05-0700] > The situation is rather murky, at best. > > http://www.w3.org/TR/REC-xml/#charsets votes 2 (text definition and comment) > to 1 (grammar) for allowing control characters: > > 2.2 Characters > > [Definition: A parsed entity contains text, a sequence of characters, which > may represent markup or character data.] > [Definition: A character is an atomic unit of text as specified by ISO/IEC > 10646:2000 [ISO/IEC 10646]. Legal characters are tab, carriage return, line > feed, and the legal characters of Unicode and ISO/IEC 10646. The versions of > these standards cited in A.1 Normative References were current at the time > this document was prepared. New characters may be added to these standards > by amendments or new editions. Consequently, XML processors MUST accept any > character in the range specified for Char. ] > Character Range > > [2] Char ::= #x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | > [#x10000-#x10FFFF] > /* any Unicode character, excluding the surrogate blocks, FFFE, and FFFF. */ > > > http://www.unicode.org/charts/PDF/U0000.pdf shows that ASCII > control characters (including 0x0) are Unicode characters. I think the above makes it pretty clear that our literals are sequences of unicode character, not sequences of XML Chars. Yet we call them xs:strings. > I wonder how many XML processors forbid control characters. at least LibXML and Expat: DB<1> use XML::LibXML DB<2> p $dom = XML::LibXML->load_xml(string => '<a></a>'); :1: parser error : PCDATA invalid Char value 1 <a></a> ^ DB<3> use XML::Parser DB<4> $p1 = new XML::Parser(Style => 'Debug') DB<5> p $p1->parse('<a></a>') not well-formed (invalid token) at line 1, column 3, byte 3 at /usr/lib/perl5/XML/Parser.pm line 187 > Unfortunately, the public version of ISO 10646 does not appear to be > currently accessible. It *is* annoying for a W3C standard to point to > another standard whose master version is not freely available. yeah, that's why I always look at the unicode code charts (as you apparently did above). > peter > > > > > > > On Wed, Apr 10, 2013 at 12:38 PM, Eric Prud'hommeaux <eric@w3.org> wrote: > > > Tests like LITERAL1_all_controls include control codes not allowed in > > xsd:string. XSD says that xsd:strings are XML character data: > > > > [[ > > The ·value space· of string is the set of finite-length sequences of > > characters (as defined in [XML 1.0 (Second Edition)]) that ·match· > > the Char production from [XML 1.0 (Second Edition)]. > > ]] — http://www.w3.org/TR/xmlschema-2/#string > > > > XML character data excludes non-whitespaec control characters: > > > > [[ > > A parsed entity contains text…Legal characters are tab, carriage > > return, line feed, and the legal characters of Unicode and ISO/IEC > > 10646. > > ]] — http://www.w3.org/TR/REC-xml/#dt-character > > > > Points 4 below explain why this calls into question whether any > > string can contain (so called "C0") control codes and be typed as > > an xsd:string. > > > > I have to say, I've always appreciated that RDF doesn't make me > > uu-encode or invent escaping mechanisms all the time like XML does; > > this control code issue is tied to a behavior which makes RDF > > (e.g. Turtle) considerably more flexible and easy to deal with. > > > > > > * Eric Prud'hommeaux <eric@w3.org> [2013-04-07 17:55-0400] > > > I've had these niggling doubts for a while, and finally succumbed to > > > that morbid desire to explore some problems that I'd rather not know > > > about. We've all known for a while that we can create graphs with APIs > > > (now even serializable in Turtle) which can't be written in RDF/XML. > > > Here's a list of issues I think we need to clarify: > > > > > > > > > > > > 1 Namespaces are OK syntactically[nssyn], though our notion of namespace > > > IRIs is of course outside the Namespaces definition as URIs [nsURI]. > > > [nssyn] http://www.w3.org/TR/REC-xml-names/#NT-Attribute > > > [nsURI] http://www.w3.org/TR/REC-xml-names/#dt-namespace > > > > > > ------------------------------------------------------------ > > > > > > > > > 2 QNames forbid a raft of [first] and [nth] characters which are > > > permissible in [IRIs]. > > > > > > first: [A-Z] | "_" | [a-z] | [#xC0-#xD6] | [#xD8-#xF6] | > > > [#xF8-#x2FF] | [#x370-#x37D] | [#x37F-#x1FFF] | > > > [#x200C-#x200D] | [#x2070-#x218F] | [#x2C00-#x2FEF] | > > > [#x3001-#xD7FF] | [#xF900-#xFDCF] | [#xFDF0-#xFFFD] | > > > [#x10000-#xEFFFF] > > > > > > nth: first | "-" | "." | [0-9] | #xB7 | [#x0300-#x036F] | > > > [#x203F-#x2040] > > > http://www.w3.org/TR/REC-xml-names/#NT-NCName > > > > > > IRIs: ipchar = [A-Z] | "_" | [a-z] | [0-9] | "-" | "." "~" | > > > "%" HEX HEX | "!" | "$" | "&" | "'" | "(" | ")" | > > > "*" | "+" | "," | ";" | "=" | ":" | "@" | > > > [#xA0-#xD7FF] | [#xF900-#xFDCF] | [#xFDF0-#xFFEF] | > > > [#x10000-#x1FFFD] | [#x20000-#x2FFFD] | > > > [#x30000-#x3FFFD] | [#x40000-#x4FFFD] | > > > [#x50000-#x5FFFD] | [#x60000-#x6FFFD] | > > > [#x70000-#x7FFFD] | [#x80000-#x8FFFD] | > > > [#x90000-#x9FFFD] | [#xA0000-#xAFFFD] | > > > [#xB0000-#xBFFFD] | [#xC0000-#xCFFFD] | > > > [#xD0000-#xDFFFD] | [#xE1000-#xEFFFD] > > > http://tools.ietf.org/html/rfc3987#section-2.2 > > > > > > ------------------------------------------------------------ > > > > > > > > > 3 XML content excludes [#x00-#x08] [#x0B-#x0C] [#x0E-#x1F], all of > > > which are permitted in "Unicode strings" and thus RDF literals > > > [Rlit]. This applies regardless of CDATA enclosure or entity > > > substitution. > > > [Rlit] > > https://dvcs.w3.org/hg/rdf/raw-file/default/rdf-concepts/index.html#dfn-lexical-form > > > [2] Char ::= #x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | > > > [#x10000-#x10FFFF] > > > http://www.w3.org/TR/2000/WD-xml-2e-20000814#NT-Char > > > > > > ------------------------------------------------------------ > > > > > > > > > 4 XML Schema also prohibits the above control characters from > > > appearing in something typed as xsd:string [string]. > > > [string] http://www.w3.org/TR/xmlschema-2/#dt-string > > > > > > ------------------------------------------------------------ > > > > > > > > > For 4, I propose notes in RDF Concepts and the serialization syntaxes > > > (e.g. Turtle). For the others, I wonder if we're forced into some > > > miserable escaping mechanism applied on top of XML. > > > > > > -- > > > -ericP > > > > -- > > -ericP > > > > -- -ericP
Received on Wednesday, 10 April 2013 20:47:00 UTC