Network Working Group                                         J. Reschke
Internet-Draft                                                greenbytes
Expires: February 6, 2002                                 August 8, 2001


                    Datatypes for WebDAV properties
               draft-reschke-webdav-property-datatypes-00

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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   This Internet-Draft will expire on February 6, 2002.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

   This specification extends the WebDAV Distributed Authoring Protocol
   to support datatyping on property values.  Protocol elements are
   defined to let clients and servers specify the type of a property,
   and to instruct the WebDAV method PROPFIND to return datatype
   information.

   Distribution of this document is unlimited.  Please send comments to
   the Distributed Authoring and Versioning (WebDAV) working group at
   w3c-dist-auth@w3.org[1], which may be joined by sending a message
   with subject "subscribe" to w3c-dist-auth-request@w3.org[2].

   Discussions of the WEBDAV working group are archived at URL:



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   http://lists.w3.org/Archives/Public/w3c-dist-auth/.

Table of Contents

   1.  Notational Conventions . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Overview of data types . . . . . . . . . . . . . . . . . . . .  5
   4.  Changes for PROPPATCH method . . . . . . . . . . . . . . . . .  6
   4.1 Example for successful PROPPATCH . . . . . . . . . . . . . . .  6
   4.2 Example for failed PROPPATCH . . . . . . . . . . . . . . . . .  7
   4.3 Example for succesful PROPPATCH where type information was
       not preserved  . . . . . . . . . . . . . . . . . . . . . . . .  8
   5.  Changes for PROPFIND method  . . . . . . . . . . . . . . . . . 10
   5.1 Example for PROPFIND/prop  . . . . . . . . . . . . . . . . . . 10
   6.  Compatibility Considerations . . . . . . . . . . . . . . . . . 12
   7.  Internationalization Considerations  . . . . . . . . . . . . . 13
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   9.  Copyright  . . . . . . . . . . . . . . . . . . . . . . . . . . 15
   10. Intellectual Property  . . . . . . . . . . . . . . . . . . . . 16
       References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
       Author's Address . . . . . . . . . . . . . . . . . . . . . . . 17
       Full Copyright Statement . . . . . . . . . . . . . . . . . . . 18





























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1. Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   The term "property element" refers to the XML element that identifies
   a particular property, for instance

   	<getcontentlength xmlns="DAV:" />

   The term "prop element" is used for the WebDAV "prop" element as
   defined in section 12.11 of [RFC2518].

   The XML representation of schema components uses a vocabulary
   identified by the namespace name "http://www.w3.org/2001/XMLSchema".
   For brevity, the text and examples in this specification use the
   prefix "xs:" to stand for this namespace; in practice, any prefix can
   be used.  "XML Schema: Structures" ([XS1]) also defines several
   attributes for direct use in any XML documents.  These attributes are
   in a different namespace, which has the namespace name
   "http://www.w3.org/2001/XMLSchema-instance".  For brevity, the text
   and examples in this specification use the prefix "xsi:" to stand for
   this latter namespace; in practice, any prefix can be used.



























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2. Introduction

   This specification builds on the infrastructure provided by the
   WebDAV Distributed Authoring Protocol, adding support data-typed
   properties.

   Although servers must support XML content in property values, it may
   be desirable to persist values as scalar values when possible, and to
   expose the data's type when the property value is returned to the
   client.  The client is free to ignore this information, but it may be
   able to take advantage of it when modifying a property.

   On the other hand, when setting new properties, it can be desirable
   to pass data type information along with the value.  A server can
   take advantage of this information to optimize storage and to perform
   additional parsing (for instance of dates).  Servers that support
   searching can also take advantage of known data types when doing
   comparisons and sorting.

































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3. Overview of data types

   Although WebDAV property types can be anything that can be marshalled
   as content of an XML element, in many cases they actually are simple
   types like integers, booleans or dates.  "XML Schema Part 2:
   Datatypes" [XS2] defines a set of simple types which can be used as a
   basis for supplying type information to attributes.

   Data type information is represented using the attribute "type" from
   the XML Schema namespace "http://www.w3.org/2001/XMLSchema-instance".
   In XML Schema, data types are qualified names, and the XML Schema
   recommendation defines a set of built-in datatypes (section 3 of
   [XS2]), defined in the namespace "http://www.w3.org/2001/XMLSchema".

   To avoid unnecessary verbosity, data type information should only be
   supplied if it adds usable information to the protocol.  In
   particular, type information is not required for live properties
   defined in WebDAV [RFC2518] and for properties of type "xs:string".

   A server may implement any combination of datatypes, both from the
   XML Schema recommendation and possibly from other namespaces.

   Note that a particular property can be typed for a number of reasons:

   o  The property is a live property with server-defined semantics and
      value space.

   o  The property may have been set using a non-WebDAV protocol that
      the server understands in addition to WebDAV.

   o  The type may have been specified in an extended PROPPATCH method
      as defined in Section 4.



















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4. Changes for PROPPATCH method

   If the property element has an XML attribute named "xsi:type", the
   server may use this information to select an optimized representation
   for storing the property value.  For instance, by specifying a type
   as "xs:boolean", the client declares the property value to be of type
   boolean (as defined in [XS2]).  The server may choose any suitable
   internal format for persisting this property, and in particular is
   allowed to fail the request if the format given does not fit the
   format defined for this type.

   The server should indicate successful detection and parsing of the
   typed value by setting the xsi:type attribute on the property element
   in the response body (this implies that it should return a
   MULTISTATUS status code and a <multistatus> response body).

4.1 Example for successful PROPPATCH

    >>Request

      PROPPATCH /bar.html HTTP/1.1
      Host: www.foo.com
      Content-Type: text/xml
      Content-Length: xxxx

      <D:propertyupdate xmlns:D="DAV:"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns:xs="http://www.w3.org/2001/XMLSchema"
         xmlns:Z="http://www.w3.com/standards/z39.50">
        <D:set>
          <D:prop>
            <Z:released xsi:type="xs:boolean">false</Z:released>
          </D:prop>
        </D:set>
      </D:propertyupdate>
















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    >>Response

      HTTP/1.1 207 Multi-Status
      Content-Type: text/xml
      Content-Length: xxxx

      <D:multistatus xmlns:D="DAV:"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns:xs="http://www.w3.org/2001/XMLSchema"
         xmlns:Z="http://www.w3.com/standards/z39.50">
        <D:response>
          <D:href>http://www.foo.com/bar.html</D:href>
          <D:propstat>
            <D:prop><Z:released xsi:type="xs:boolean" /></D:prop>
            <D:status>HTTP/1.1 200 OK</D:status>
           </D:propstat>
        </D:response>
      </D:multistatus>

   In this cases, the xsi:type attribute on the element "Z:released"
   indicates that the server indeed has understood the submitted data
   type information.

4.2 Example for failed PROPPATCH

    >>Request

      PROPPATCH /bar.html HTTP/1.1
      Host: www.foo.com
      Content-Type: text/xml
      Content-Length: xxxx

      <D:propertyupdate xmlns:D="DAV:"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns:xs="http://www.w3.org/2001/XMLSchema"
         xmlns:Z="http://www.w3.com/standards/z39.50">
        <D:set>
          <D:prop>
            <Z:released xsi:type="xs:boolean">t</Z:released>
          </D:prop>
        </D:set>
      </D:propertyupdate>









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    >>Response

      HTTP/1.1 207 Multi-Status
      Content-Type: text/xml
      Content-Length: xxxx

      <D:multistatus xmlns:D="DAV:"
         xmlns:Z="http://www.w3.com/standards/z39.50">
        <D:response>
          <D:href>http://www.foo.com/bar.html</D:href>
          <D:propstat>
            <D:prop><Z:released/></D:prop>
            <D:status>HTTP/1.1 422 Unprocessable Entity</D:status>
            <D:responsedescription>Does not parse as xs:boolean</D:responsedescription>
          </D:propstat>
        </D:response>
      </D:multistatus>

   In this case the request failed because the supplied value "t" is not
   a valid representation for a boolean value.

   Note that similar error conditions can occur in the standard WebDAV
   protocol even though no data type was specified: for instance, when a
   client tries to set a live property for which only a certain value
   space is allowed.

4.3 Example for succesful PROPPATCH where type information was not
    preserved

    >>Request

      PROPPATCH /bar.html HTTP/1.1
      Host: www.foo.com
      Content-Type: text/xml
      Content-Length: xxxx

      <D:propertyupdate xmlns:D="DAV:"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns:Z="http://www.w3.com/standards/z39.50">
        <D:set>
          <D:prop>
            <Z:released xsi:type="Z:custom">t</Z:released>
          </D:prop>
        </D:set>
      </D:propertyupdate>






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    >>Response

      HTTP/1.1 207 Multi-Status
      Content-Type: text/xml
      Content-Length: xxxx

      <D:multistatus xmlns:D="DAV:"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns:Z="http://www.w3.com/standards/z39.50">
        <D:response>
          <D:href>http://www.foo.com/bar.html</D:href>
          <D:propstat>
            <D:prop><Z:released/></D:prop>
            <D:status>HTTP/1.1 200 OK</D:status>
           </D:propstat>
        </D:response>
      </D:multistatus>

   In this case the request succeeded, but the server did not know how
   to handle the data type "Z:custom".  Therefore no data type
   information was returned in the response body.






























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5. Changes for PROPFIND method

   PROPFIND is extended to return the data type information for
   properties unless one of the following conditions is met:

   o  The data type MUST be different from "xs:string" (because this can
      be considered the default data type).

   o  The property's data type MUST not be defined in [RFC2518] (because
      these types are already well-defined).


5.1 Example for PROPFIND/prop

   >>Request

      PROPFIND /bar.html HTTP/1.1
      Host: www.foo.com
      Content-Type: text/xml
      Content-Length: xxxx

      <D:propfind xmlns:D="DAV:" xmlns:Z="http://www.w3.com/standards/z39.50">
        <D:prop>
          <D:getcontenttype/>
          <Z:released/>
        </D:prop>
      </D:propfind>
























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    >>Response

      HTTP/1.1 207 Multi-Status
      Content-Type: text/xml
      Content-Length: xxxx

      <D:multistatus xmlns:D="DAV:" xmlns:Z="http://www.w3.com/standards/z39.50"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns:xs="http://www.w3.org/2001/XMLSchema">
        <D:response>
          <D:href>http://www.foo.com/bar.html</D:href>
          <D:propstat>
            <D:prop>
              <D:getcontenttype>text/html</D:getcontenttype>
              <Z:released xsi:type="xs:boolean">1</Z:released>
            </D:prop>
            <D:status>HTTP/1.1 200 OK</D:status>
          </D:propstat>
        </D:response>
      </D:multistatus>

   This example shows that the property value "true" is returned with
   the correct data type information, and that the server chose one of
   the two possible representations defined in XML Schema.  It also
   shows that data type information is not returned for
   "D:getcontenttype", as this property's data type is already defined
   in [RFC2518].
























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6. Compatibility Considerations

   This specification does not introduce any new protocol elements, nor
   does it change the informal WebDAV DTD.  It merely specifies
   additional server semantics for the case where clients submit
   additional data type information in an attribute on the property
   element (previously undefined), and adds an additional attribute on
   property elements upon PROPFIND.

   Clients not aware of this specification should not supply the
   "xsi:type" attribute on property elements (after all, this attribute
   belongs to the XML Schema-Instance namespace which has been defined
   for exactly this purpose).  Old clients should also ignore additional
   attributes on property elements returned by PROPFIND (and similar
   methods), although the WebDAV specification only defines this
   behaviour for unknown elements (and is silent about unknown
   attributes).

   Servers not aware of this specification either drop the "xsi:type"
   attribute, or persist it along with the property value.  However,
   they will never indicate successful parsing of the data type by
   returning back the type in the response to PROPPATCH.





























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7. Internationalization Considerations

   This proposal builds on [RFC2518], and inherits its
   internationalizability.















































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8. IANA Considerations

   This proposal does not introduce any new IANA considerations, since
   it does not specify any new namespaces (in the general sense), but
   merely uses existing ones.














































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9. Copyright

   To be supplied by the RFC Editor.
















































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10. Intellectual Property

   To be supplied by the RFC Editor.
















































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References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [XML]      Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E. and
              , "Extensible Markup Language (XML) 1.0", W3C XML,
              February 1998, <http://www.w3.org/TR/1998/REC-xml-
              19980210>.

   [XS1]      Thompson, H., Beech, D., Maloney, M., Mendelsohn, N. and
              , "XML Schema Part 1: Structures", W3C XS1, May 2001,
              <http://www.w3.org/TR/xmlschema-1/>.

   [XS2]      Biron, P., Malhotra, A. and  , "XML Schema Part 2:
              Datatypes", W3C XS2, May 2001,
              <http://www.w3.org/TR/xmlschema-2/>.

   [RFC2518]  Goland, Y., Whitehead, E., Faizi, A., Carter, S. and D.
              Jensen, "HTTP Extensions for Distributed Authoring --
              WEBDAV", RFC 2518, February 1999.

   [1]  <mailto:w3c-dist-auth@w3.org>

   [2]  <mailto:w3c-dist-auth-request@w3.org?subject=subscribe>


Author's Address

   Julian F. Reschke
   greenbytes GmbH
   Salzmannstrasse 152
   Muenster, NW  48159
   Germany

   EMail: julian.reschke@greenbytes.de















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Full Copyright Statement

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
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   The limited permissions granted above are perpetual and will not be
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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