- From: dehora <dehora@eircom.net>
- Date: Fri, 14 Sep 2001 05:19:10 +0100
- To: "W3C Rdfcore" <w3c-rdfcore-wg@w3.org>
"Prepare a proposal for namespace qualification values of rdf:parseType attributes upon which the group can make a decision." Forces: parseType="Literal" is, in the of words the M&S, "a minimum-level solution to the requirement to express an RDF statement with a value that has XML markup. Additional complexities of XML such as canonicalization of whitespace are not yet well defined. Future work of the W3C is expected to resolve such issues in a uniform manner for all applications based on XML." Ongoing proposals in the wg may lead to the interpretation that the fundamental representation of a literal is a Unicode string with optional language tag upon which serializations might have to impose syntactic constraints. This is not catered for in the current M&S XML syntax. There is interest in treating XML literal element content as something other than well formed XML (such as infoset). There may be interest in the future to apply well known data types over literals. Any future RDF recommendation should recognise practice, notably by the DAML effort, which is using parseType as extensibility mechanism beyond that mandated by the current M&S. Further the wg should indicate an appropriate method for people wishing to extend parseType. Clearly, changes to the existing interpretation of the parseType attribute value Literal will be backwards incompatible with current processors and RDF-XML data modelling assumptions. Therefore, the interpretations and reservation of both the attribute values Literal and Resource must stand. The following is the key text in M&S re RDF-XML parseType: "(P203) The parseType attribute changes the interpretation of the element content. The parseType attribute should have one of the values 'Literal' or' Resource'. The value is case-sensitive. The value 'Literal' specifies that the element content is to be treated as an RDF/XML literal; that is, the content must not be interpreted by an RDF processor. The value 'Resource' specifies that the element content must be treated as if it were the content of a Description element. Other values of parseType are reserved for future specification by RDF. With RDF 1.0 other values must be treated as identical to 'Literal'. In all cases, the content of an element having a parseType attribute must be well-formed XML. The content of an element having a parseType="Resource" attribute must further match the production for the content of a Description element. The RDF Model and Syntax Working Group acknowledges that the parseType='Literal' mechanism is a minimum-level solution to the requirement to express an RDF statement with a value that has XML markup. Additional complexities of XML such as canonicalization of whitespace are not yet well defined. Future work of the W3C is expected to resolve such issues in a uniform manner for all applications based on XML. Future versions of RDF will inherit this work and may extend it as we gain insight from further application experience." Proposed revised and extended wording. Please note that (p4) is largely illustrative at this point and could reasonably be excised with the other paragraphs remain in place: (p1) The parseType attribute changes the interpretation of the element content. (p2) It is recognized that parseType is useful as an extensibility mechanism. The preferred technique to extend parseType is through the use of qualified names, as discussed in the XML Namespaces recommendation. The purpose of using namespaces to denote parseType values is to allow extensions to be associated with a vocabulary or schema. Note: the XML namespaces notion of default namespaces shall not apply to parseType values, in precisely the same sense that default namespaces does not apply to attributes. Unqualified values of parseType must not considered to be in any namespace. (p3) The non-namespaced values specified are 'Literal' and 'Resource'. The values are case-sensitive. The value 'Literal' specifies that the element content is to be treated as an RDF literal. The element content is considered opaque: that is, it must not be interpreted or passed on by an RDF processor as RDF. The element content however must be well formed XML and there are syntactic constraints imposed by this serialization [see fixme]. The value 'Resource' specifies that the element content must be treated as if it were the content of a Description element. The content of an element having a parseType="Resource" attribute must further match the production for the content of a Description. (p4) The local part values specified are 'literal', 'resource' and 'canonical'. These three are bound to the RDF namespace [fixme]. By convention, the prefix 'rdf' is used as the namespace qualifier, although any prefix can be used. Future editions of this document may add new local parts as deemed appropriate. The local part 'literal' has the same interpretation as 'Literal'. The local part 'resource' has the same interpretation as 'Resource'. The local part 'canonical' specifies that the literal should be treated as canonical XML [see fixme]; fixme: more+markup examples. (p5) An RDF-XML processor encountering an unrecognised parseType value must continue to behave as if that value was 'Literal'. Note: how XML attributes which affect the interpretation of literals are passed along is not specified in this document (xml:lang is another case in point). Nonetheless processors which find unrecognised parseType values should pass on the found parseType value rather than the default case 'Literal', where they are capable of doing so. Bill de hÓra
Received on Friday, 14 September 2001 00:20:40 UTC