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Syntax Issues

From: Juergen Reuter <reuterj@ira.uka.de>
Date: Wed, 17 Nov 1999 18:56:29 +0100
To: WebDAV WG <w3c-dist-auth@w3.org>
cc: reuterj@ira.uka.de, jjh@ira.uka.de
Message-ID: <"iraun1.ira.486:"@ira.uka.de>
Hi all!

While trying to implement a WebDAV/DeltaV based C/S application,
some parsing related questions arose that I would like to have
clarified, if possible.  In the mailing archive with recent postings
of this list, I did not find any related topic, but I may have
overseen some posting and would also be grateful for any reference.

N.B.: [WebDAV] means RFC 2518, [XML] REC-xml-19980210,
[Namespaces] REC-xml-names-19990114, and [HTTP] RFC 2068.

1. [WebDAV] section 23.1 (appendix 1), and 12.12.1:
   As far as I understand [XML], the declaration
   <!ELEMENT keepalive (#PCDATA | href+) >
   is not a valid xml element declaration.  The use of both,
   #PCDATA and children content href implies a mixed content
   declaration.  For mixed content, [XML] section 3.2.2 defines
   [51] Mixed ::= '(' S? '#PCDATA' (S? '|' S? Name)* S? ')*'
                  | '(' S? '#PCDATA' S? ')'.
   Hence, element keepalive may be declared as
   <!ELEMENT keepalive (#PCDATA | href)* >
   which is a more general form and might need to be further
   restricted to its originally intended syntax on the semantic
   level of the specification.

   Alternatively, one could specify
   <!ELEMENT keepalive (all | href+) >
   where element all would effectively replace the '"*"'
   PCDATA of the keepalive element.

2. At a first look, [WebDAV] section 23.1 seems to present the
   syntax in the style of a document type declaration as specified
   in [XML] section 2.8, rule [28] (doctypedecl definition).
   If this is intended, "the Name in the document type declaration
   must match the element type of the root element" (cited from
   [XML] validity constraint: root element type).  Effectively,
   this would mean, that there must be an element named webdav-1.0
   which serves as root element.  However, I can not find an element
   declaration of the form <!ELEMENT webdav-1.0 ... >.  Instead,
   the examples in [WebDAV] seem to use elements propfind,
   multistatus, propertyupdate, propertybehaviour, lockinfo and prop
   as varying root elements.  Hence, could an additional element
   declaration such as
   <!ELEMENT webdav-1.0 (propfind | multistatus |
   propertyupdate | propertybehaviour | lockinfo | prop) >
   solve this problem?

3. The xml code in the examples in chapter 8 of [WebDAV] should, if I
   understand right, be compliant with the syntax specified in
   appendix 1.  Section 2.8 of [XML] says:
   "An XML document is valid if it has an associated document type
   declaration and if the document complies with the constraints
   expressed in it."
   Without supplying a DTD, the document can only be checked for
   well-formedness, which does not seem to help very much for
   real-life applications.  Hence, I would expect the xml code of
   the examples in chapter 8 of [WebDAV] to begin as follows or
   the like:
   <?xml version="1.0" encoding="utf-8" ?>
   <!DOCTYPE webdav-1.0 PUBLIC "-//W3C/DTD webdav-1.0//EN"
   According to the root element issue (see above), I would expect then
   followed by the lines as supplied in the examples in chapter 8,
   and then followed by
   which terminates the xml code.

4. The response in the example in section 8.1.1 [WebDAV] contains
   the line
   As far as I understand, R as an undeclared namespace prefix,
   as there is no declared R namespace in scope.  The line should
   propably read as follows:
   <D:prop xmlns:R="http://www.foo.bar/boxschema/">

5. Section 9.1 of [WebDAV] defines the DAV header as follows:
   DAV = "DAV" ":" "1" ["," "2"] ["," 1#extend]
   I could not find any syntax rule for extend, neither in
   [WebDAV], nor in [HTTP].  If extend may contain a ",", this
   may lead to ambigous parsing; e.g. the string "DAV:1,2,3" could
   be parsed with "2,3" representing the extend non-terminal.  Hence,
   if extend has not been defined by now, it should at least be
   further restricted, e.g. by requiring extend = token or
   extend = quoted-string, with token and quoted-string being
   defined in [HTTP].

6. Is there a specific reason for WebDAV not making use of xml
   element attributes?  I think, using attributes could both, speed
   up parsing and simplify the grammar.
   For example, elements exclusive and shared could be replaced by
   a single enumerated attribute (see [XML] section 3.3.1, rule [57]
   EnumeratedType) for element lockscope.

I hope I could present my issues clearly enough.
Many thanks in advance!

Received on Wednesday, 17 November 1999 13:00:17 GMT

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