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rfc:rfc4316

Network Working Group J. Reschke Request for Comments: 4316 greenbytes Category: Experimental December 2005

  Datatypes for Web Distributed Authoring and Versioning (WebDAV)
                             Properties

Status of This Memo

 This memo defines an Experimental Protocol for the Internet
 community.  It does not specify an Internet standard of any kind.
 Discussion and suggestions for improvement are requested.
 Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2005).

Abstract

 This specification extends the Web Distributed Authoring and
 Versioning Protocol (WebDAV) to support datatyping.  Protocol
 elements are defined to let clients and servers specify the datatype,
 and to instruct the WebDAV method PROPFIND to return datatype
 information.

Table of Contents

 1. Introduction ....................................................2
 2. Notational Conventions ..........................................2
 3. Overview ........................................................3
 4. Changes for PROPPATCH Method ....................................4
    4.1. Example of Successful PROPPATCH ............................4
    4.2. Example of Failed PROPPATCH ................................5
    4.3. Example of Successful PROPPATCH Where Type
         Information Was Not Preserved ..............................6
 5. Changes for PROPFIND Method .....................................7
    5.1. Example of PROPFIND/prop ...................................7
 6. Changes for Other Methods .......................................8
 7. Compatibility Considerations ....................................8
 8. Internationalization Considerations .............................9
 9. Security Considerations .........................................9
 10. Acknowledgements ...............................................9
 11. References .....................................................9
    11.1. Normative References ......................................9
    11.2. Informative References ....................................9

Reschke Experimental [Page 1] RFC 4316 Datatypes for WebDAV Properties December 2005

1. Introduction

 This specification builds on the infrastructure provided by the Web
 Distributed Authoring and Versioning (WebDAV) Protocol, adding
 support for 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 datatype 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 datatypes when doing
 comparisons and sorting.
 The following potential datatyping-related features were deliberately
 considered out of scope:
 o  getting "schema" information for classes of resources (set of
    "required" properties, their types, display information),
 o  definition of a set of mandatory property types,
 o  discovery of supported property types,
 o  extensions to PROPPATCH that would allow updates to parts of a
    (structured) property.

2. 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".

Reschke Experimental [Page 2] RFC 4316 Datatypes for WebDAV Properties December 2005

 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 Part 1: Structures" ([XS1]) also defines
 several attributes for direct use in any XML documents.  These
 attributes are in a different namespace named
 "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.

3. Overview

 Although WebDAV property types can be anything that can be marshaled
 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 that can be used as a
 basis for supplying type information to attributes.
 Datatype information is represented using the attribute "type" from
 the XML Schema namespace "http://www.w3.org/2001/XMLSchema-instance".
 In XML Schema, datatypes 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, datatype 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.

Reschke Experimental [Page 3] RFC 4316 Datatypes for WebDAV Properties December 2005

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 of Successful PROPPATCH

 >>Request
 PROPPATCH /bar.html HTTP/1.1
 Host: example.org
 Content-Type: text/xml; charset="utf-8"
 Content-Length: xxxx
 <?xml version="1.0" encoding="utf-8" ?>
 <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://ns.example.org/standards/z39.50">
   <D:set>
     <D:prop>
       <Z:released xsi:type="xs:boolean">false</Z:released>
     </D:prop>
   </D:set>
 </D:propertyupdate>
 >>Response
 HTTP/1.1 207 Multi-Status
 Content-Type: text/xml; charset="utf-8"
 Content-Length: xxxx
 <?xml version="1.0" encoding="utf-8" ?>
 <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://ns.example.org/standards/z39.50">

Reschke Experimental [Page 4] RFC 4316 Datatypes for WebDAV Properties December 2005

   <D:response>
     <D:href>http://example.org/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 case, the xsi:type attribute on the element "Z:released"
 indicates that the server indeed has understood the submitted data
 type information.

4.2. Example of Failed PROPPATCH

 >>Request
 PROPPATCH /bar.html HTTP/1.1
 Host: example.org
 Content-Type: text/xml; charset="utf-8"
 Content-Length: xxxx
 <?xml version="1.0" encoding="utf-8" ?>
 <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://ns.example.org/standards/z39.50">
   <D:set>
     <D:prop>
       <Z:released xsi:type="xs:boolean">t</Z:released>
     </D:prop>
   </D:set>
 </D:propertyupdate>
 >>Response
 HTTP/1.1 207 Multi-Status
 Content-Type: text/xml; charset="utf-8"
 Content-Length: xxxx
 <?xml version="1.0" encoding="utf-8" ?>
 <D:multistatus xmlns:D="DAV:"
    xmlns:Z="http://ns.example.org/standards/z39.50">
   <D:response>
     <D:href>http://example.org/bar.html</D:href>
     <D:propstat>
       <D:prop><Z:released/></D:prop>
       <D:status>HTTP/1.1 422 Unprocessable Entity</D:status>

Reschke Experimental [Page 5] RFC 4316 Datatypes for WebDAV Properties December 2005

       <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 datatype 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 of Successful PROPPATCH Where Type Information Was Not

    Preserved
 >>Request
 PROPPATCH /bar.html HTTP/1.1
 Host: example.org
 Content-Type: text/xml; charset="utf-8"
 Content-Length: xxxx
 <?xml version="1.0" encoding="utf-8" ?>
 <D:propertyupdate xmlns:D="DAV:"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:Z="http://ns.example.org/standards/z39.50">
   <D:set>
     <D:prop>
       <Z:released xsi:type="Z:custom">t</Z:released>
     </D:prop>
   </D:set>
 </D:propertyupdate>
 >>Response
 HTTP/1.1 207 Multi-Status
 Content-Type: text/xml; charset="utf-8"
 Content-Length: xxxx
 <?xml version="1.0" encoding="utf-8" ?>
 <D:multistatus xmlns:D="DAV:"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:Z="http://ns.example.org/standards/z39.50">
   <D:response>
     <D:href>http://example.org/bar.html</D:href>

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     <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 datatype "Z:custom".  Therefore, no datatype
 information was returned in the response body.

5. Changes for PROPFIND Method

 PROPFIND is extended to return the datatype information for
 properties by adding "xsi:type" attributes to the property elements
 unless one of the following conditions is met:
 o  The datatype MUST be different from "xs:string" (because this can
    be considered the default datatype).
 o  The property's datatype MUST NOT be defined in [RFC2518] (because
    these types are already well-defined).

5.1. Example of PROPFIND/prop

 >>Request
 PROPFIND /bar.html HTTP/1.1
 Host: example.org
 Content-Type: text/xml; charset="utf-8"
 Content-Length: xxxx
 <?xml version="1.0" encoding="utf-8" ?>
 <D:propfind xmlns:D="DAV:"
   xmlns:Z="http://ns.example.org/standards/z39.50">
   <D:prop>
     <D:getcontenttype/>
     <Z:released/>
   </D:prop>
 </D:propfind>
 >>Response
 HTTP/1.1 207 Multi-Status
 Content-Type: text/xml; charset="utf-8"
 Content-Length: xxxx
 <?xml version="1.0" encoding="utf-8" ?>

Reschke Experimental [Page 7] RFC 4316 Datatypes for WebDAV Properties December 2005

 <D:multistatus xmlns:D="DAV:"
    xmlns:Z="http://ns.example.org/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://example.org/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 datatype information and that the server chose one of the
 two possible representations defined in XML Schema.  It also shows
 that datatype information is not returned for "D:getcontenttype", as
 this property's datatype is already defined in [RFC2518].

6. Changes for Other Methods

 Servers that support other methods using the DAV:multistatus response
 format (such as the REPORT method defined in [RFC3253], Section 3.6)
 SHOULD apply the same extensions as defined in Section 5.

7. Compatibility Considerations

 This part of 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 datatype information in an attribute on the
 property element (previously undefined), and adds an additional
 attribute on property elements upon PROPFIND.
 Clients not aware of datatype handling 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; see [XS1], Section 2.6.1).  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 (see [RFC2518], Section 23.3.2.2).
 Servers not aware of datatype handling either drop the "xsi:type"
 attribute or have it persist along with the property value (see

Reschke Experimental [Page 8] RFC 4316 Datatypes for WebDAV Properties December 2005

 [RFC2518], Section 4.4).  However, they will never indicate
 successful parsing of the datatype by returning back the type in the
 response to PROPPATCH.  Thus, clients can supply type information
 without having to poll for server support in advance.

8. Internationalization Considerations

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

9. Security Considerations

 This protocol extension does not introduce any new security
 implications beyond those documented for the base protocol (see
 [RFC2518], Section 17).

10. Acknowledgements

 This document has benefited from thoughtful discussion by Lisa
 Dusseault, Stefan Eissing, Eric Sedlar, and Kevin Wiggen.

11. References

11.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2518]  Goland, Y., Whitehead, E., Faizi, A., Carter, S., and D.
            Jensen, "HTTP Extensions for Distributed Authoring --
            WEBDAV", RFC 2518, February 1999.
 [XS1]      Thompson, H., Beech, D., Maloney, M., Mendelsohn, N., and
            World Wide Web Consortium, "XML Schema Part 1: Structures
            Second Edition", W3C REC-xmlschema-1-20041028,
            October 2004,
            <http://www.w3.org/TR/2004/REC-xmlschema-1-20041028/>.
 [XS2]      Biron, P., Malhotra, A., and World Wide Web Consortium,
            "XML Schema Part 2: Datatypes Second Edition", W3C REC-
            xmlschema-2-20041028, October 2004,
            <http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/>.

11.2. Informative References

 [RFC3253]  Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J.
            Whitehead, "Versioning Extensions to WebDAV", RFC 3253,
            March 2002.

Reschke Experimental [Page 9] RFC 4316 Datatypes for WebDAV Properties December 2005

Author's Address

 Julian F. Reschke
 greenbytes GmbH
 Hafenweg 16
 Muenster, NW  48155
 Germany
 Phone: +49 251 2807760
 Fax:   +49 251 2807761
 EMail: julian.reschke@greenbytes.de
 URI:   http://greenbytes.de/tech/webdav/

Reschke Experimental [Page 10] RFC 4316 Datatypes for WebDAV Properties December 2005

Full Copyright Statement

 Copyright (C) The Internet Society (2005).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78 and at www.rfc-editor.org/copyright.html, and
 except as set forth therein, the authors retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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 might or might not be available; nor does it represent that it has
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 on the procedures with respect to rights in RFC documents can be
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 The IETF invites any interested party to bring to its attention any
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Acknowledgement

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

Reschke Experimental [Page 11]

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