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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.486:17.11.99.17.56.42"@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+) >
   <!ELEMENT all EMPTY>
   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"
   "http://www.w3.org/TR/1999/webdav-1.0.xml">
   According to the root element issue (see above), I would expect then
   <webdav-1.0>
   followed by the lines as supplied in the examples in chapter 8,
   and then followed by
   </webdav-1.0>
   which terminates the xml code.

4. The response in the example in section 8.1.1 [WebDAV] contains
   the line
   <D:prop><R:DingALing/><R:Random/></D:prop>
   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/">
        <R:DingALing/><R:Random/>
   </D:prop>

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!

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

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