Network Working GroupJ. Reschke
Internet-Draftgreenbytes
Intended status: InformationalJune 2002
Expires: December 2002

Datatypes for WebDAV properties
draft-reschke-webdav-property-datatypes-02

Note: a later version of this document has been published as RFC4316.

Status of this Memo

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

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts.

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This Internet-Draft will expire in December 2002.

Copyright Notice

Copyright © The Internet Society (2002). All Rights Reserved.

Abstract

This specification extends the Web Distributed Authoring Protocol (WebDAV) 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, which may be joined by sending a message with subject "subscribe" to w3c-dist-auth-request@w3.org.

Discussions of the WEBDAV working group are archived at URL: http://lists.w3.org/Archives/Public/w3c-dist-auth/.


Table of Contents


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.


2. Introduction

This specification builds on the infrastructure provided by the WebDAV Distributed Authoring 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 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.


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:


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; 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://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>

>>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://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; 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://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>

>>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://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; 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://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>

>>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://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.


5. Changes for PROPFIND method

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

5.1 Example for PROPFIND/prop

>>Request

PROPFIND /bar.html HTTP/1.1
Host: www.foo.com
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://www.w3.com/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" ?>
<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].


6. Example: marshalling of array-typed properties

As an example for more complex data types, this section shows marshalling of array-typed properties as implemented in the WebDAV protocol adapters of SAP Portal's Enterprise Portal System (release 5.0).

As XML Schema [XS2] does not define simple types for arrays, it builds on the predefined array types used in [SOAP11]. These in turn can be based on the simple types defined in XML Schema.

Note the following special properties of SOAP-encoded arrays:

  1. They require an additional "arrayType" attribute to specify the array length and the base type.
  2. The names of the individual children of the property element aren't relevant as the type information is already encoded on the property element itself. It is however recommended to use identical element names for all array members.

6.1 Setting of array-typed property

>>Request

PROPPATCH /bar.html HTTP/1.1
Host: www.foo.com
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx

<?xml version="1.0" encoding="utf-8"?>
<propertyupdate xmlns="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"
   xmlns:soap-enc="http://schemas.xmlsoap.org/soap/encoding/">
  <set>
    <prop>
      <Z:refs xsi:type="soap-enc:Array"
        soap-enc:arrayType="xs:string[2]">
        <xs:string>http://www.w3.org/TR/SOAP</xs:string> 
        <xs:string>http://www.w3.org/TR/xmlschema-2</xs:string> 
      </Z:refs>
    </prop>
  </set>
</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" ?>
<multistatus xmlns="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"
   xmlns:soap-enc="http://schemas.xmlsoap.org/soap/encoding/">
  <response>
    <href>http://www.foo.com/bar.html</href>
    <propstat>
      <prop>
        <Z:refs xsi:type="soap-enc:Array"
          soap-enc:arrayType="xs:string[2]"/>
      </prop>
      <status>HTTP/1.1 200 OK</status>
     </propstat>
  </response>
</multistatus>

6.2 Getting an array-typed property

>>Request

PROPFIND /bar.html HTTP/1.1
Host: www.foo.com
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://www.w3.com/standards/z39.50">
  <D:prop>
    <Z:refs/>
  </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" ?>
<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"
   xmlns:soap-enc="http://schemas.xmlsoap.org/soap/encoding/">
  <D:response>
    <D:href>http://www.foo.com/bar.html</D:href>
    <D:propstat>
      <D:prop>
        <Z:refs xsi:type="soap-enc:Array"
          soap-enc:arrayType="xs:string[2]">
          <xs:string>http://www.w3.org/TR/SOAP</xs:string> 
          <xs:string>http://www.w3.org/TR/xmlschema-2</xs:string> 
        </Z:refs>
      </D:prop>
      <D:status>HTTP/1.1 200 OK</D:status>
    </D:propstat>
  </D:response>
</D:multistatus>

7. 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.


8. Internationalization Considerations

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


9. 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.


10. Copyright

To be supplied by the RFC Editor.


11. Intellectual Property

To be supplied by the RFC Editor.


12. References

12.1 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.
[XML]Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and World Wide Web Consortium, “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 World Wide Web Consortium, “XML Schema Part 1: Structures”, W3C XS1, May 2001, <http://www.w3.org/TR/xmlschema-1/>.
[XS2]Biron, P., Malhotra, A., and World Wide Web Consortium, “XML Schema Part 2: Datatypes”, W3C XS2, May 2001, <http://www.w3.org/TR/xmlschema-2/>.

12.2 Informative References

[SOAP11]Box, D., Ehnebuske, D., Kakivaya, G., Layman, A., Mendelsohn, N., Nielsen, H., Thatte, S., Winer, D., and World Wide Web Consortium, “Simple Object Access Protocol 1.1”, W3C Note SOAP, May 2000, <http://www.w3.org/TR/SOAP/>.

A. Change Log

A.1 Since 'draft-reschke-webdav-property-datatypes-00'

Editorial fixes.
Changed examples to explicitly use utf-8 encoding for HTTP content type and XML encoding.
Added example for marshalling array-typed properties.

A.2 Since 'draft-reschke-webdav-property-datatypes-01'

Fix width of artwork for IETF compliance.
"Non-normative references" -> "Informative references".


Author's Address

Julian F. Reschke
greenbytes GmbH
Salzmannstrasse 152
Muenster, NW 48159
Germany
Phone: +49 251 2807760
Fax: +49 251 2807761
EMail: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/

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