Datatypes for WebDAV properties

draft-reschke-webdav-property-datatypes-08

Status of this Memo

This document is an Internet-Draft and is subject to all provisions of section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668.¶

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This Internet-Draft will expire in March 2005.¶

Copyright Notice

Abstract

This specification extends the Web Distributed Authoring 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.¶

I ↓

Editorial Note
(To be removed before publication as RFC):
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 http://lists.w3.org/Archives/Public/w3c-dist-auth/.

Editorial Note (To be removed by RFC Editor before publication)

Please send comments to the Distributed Authoring and Versioning (WebDAV) working group at <mailto:w3c-dist-auth@w3.org>, which may be joined by sending a message with subject "subscribe" to <mailto:w3c-dist-auth-request@w3.org>. Discussions of the WEBDAV working group are archived at <http://lists.w3.org/Archives/Public/w3c-dist-auth/>.

Note that although discussion takes place on the WebDAV working group's mailing list, this is not a working group document.

XML versions, latest edits and the issues list for this document are available from <http://greenbytes.de/tech/webdav/#draft-reschke-webdav-property-datatypes>.

1. Introduction
2. Notational Conventions
3. Overview
4. Changes for PROPPATCH method
5. Changes for PROPFIND method
- 5.1. Example for PROPFIND/prop
6. Changes for other methods
7. Compatibility Considerations
8. Internationalization Considerations
9. IANA Considerations
10. Acknowledgements
11. References
- 11.1. Normative References
- 11.2. Informative References
Appendix A. Change Log (to be removed by RFC Editor before publication)
Author's Address
Intellectual Property and Copyright Statements

Issues list

Id	Type	Status	Date	Raised By
1_clarify_scope	change	closed	2004-09-14	lisa@osafoundation.org
7_discovery	change	closed	2004-09-14	lisa@osafoundation.org
a_remove_array_example	change	closed	2004-09-23	julian.reschke@greenbytes.de
other-method-semantics	change	closed	2004-09-15	julian.reschke@greenbytes.de
edit	edit	open	2004-07-08	julian.reschke@greenbytes.de

I edit (type: edit, status: open)
julian.reschke@greenbytes.de	2004-07-08	Umbrella issue for editorial fixes/enhancements.
Associated changes in this document: <#rfc.change.edit.1>, 3, 5, 11.1, del-1.

I other-method-semantics (type: change, status: closed)
julian.reschke@greenbytes.de	2004-09-15	Define semantics for other methods such as REPORT.
	2004-09-17	Resolution: Other methods using DAV:multistatus such as REPORT SHOULD use the same extension as defined for PROPFIND.
Associated changes in this document: <#rfc.change.other-method-semantics.1>.

1. 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.¶

I 1_clarify_scope (type: change, status: closed)
lisa@osafoundation.org	2004-09-14	Clarify what's in scope and what is not.
	2004-09-22	Resolution: Done.
Associated changes in this document: 1.

The following potential datatyping related features were deliberately considered out of scope:

getting "schema" information for classes of resources (set of "required" properties, their types, display information),
definition of a set of mandatory property types,
discovery of supported property types,
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". 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 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 marshal↑ I ↓led 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: ¶

The property is a live property with server-defined semantics and value space.
The property may have been set using a non-WebDAV protocol that the server understands in addition to WebDAV.
The type may have been specified in an extended PROPPATCH method as defined in Section 4.

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: 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">
  <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 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: 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>
      <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 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>
    <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 ↑ I ↓by adding "xsi:type" attributes to the property elements unless one of the following conditions is met: ¶

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

I 7_discovery (type: change, status: closed)
lisa@osafoundation.org	2004-09-14	Should there be a way for clients to detect whether the server supports this feature? I would think that would be better. However, if there's no way, then there should be some guidance for clients along the lines of "If the client supports this draft, the client SHOULD send data typing information for all non-string data types, without even knowing whether the server supports the feature."
	2004-09-22	Resolution: Clarify that sending the type information to un-extended servers is harmless, thus no in-advance discovery is needed.
Associated changes in this document: 7.

Servers not aware of datatype handling 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. I 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. 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. Acknowledgements

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

11. References

11.1. Normative References

↑ I ↓ [XML]: Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and F. Yergeau, “Extensible Markup Language (XML) 1.0 (Third Edition)”, W3C REC-xml-20040204, February 2004, <http://www.w3.org/TR/2004/REC-xml-20040204>.
[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”, W3C REC-xmlschema-1-20010502, May 2001, <http://www.w3.org/TR/2001/REC-xmlschema-1-20010502/>.
[XS2]: Biron, P., Malhotra, A., and World Wide Web Consortium, “XML Schema Part 2: Datatypes”, W3C REC-xmlschema-2-20010502, May 2001, <http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/>.

11.2. Informative References

I ↓ [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-20000508, May 2000, <http://www.w3.org/TR/2000/NOTE-SOAP-20000508>.
[RFC3253]: Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J. Whitehead, “Versioning Extensions to WebDAV”, RFC 3253, March 2002.

I a_remove_array_example (type: change, status: closed)
julian.reschke@greenbytes.de	2004-09-23	Remove "array" example.
	2004-09-23	Resolution: Done.
Associated changes in this document: 11.2, <#rfc.change.a_remove_array_example.2>.

↑ I

del-1. 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 ↑ I ~~SAP Portal's Enterprise Portal System (release 5.0).~~the "Knowledge Management" component inside SAP's Enterprise Portal and NetWeaver products.
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:
They require an additional "arrayType" attribute to specify the array length and the base type.
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.
del-2. Setting of array-typed property
>>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"?> <propertyupdate xmlns="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" 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://ns.example.org/standards/z39.50" xmlns:soap-enc="http://schemas.xmlsoap.org/soap/encoding/"> <response> <href>http://example.org/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>
del-3. Getting an array-typed property
>>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> <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://ns.example.org/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://example.org/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>

Appendix A. Change Log (to be removed by RFC Editor before publication)

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".¶

A.3. Since 'draft-reschke-webdav-property-datatypes-02'

Added marshalling for property flags such as "hidden" and "protected". Moved array marshalling example into back section. Added rational and description for pf:property-displayname-set. Added acknowledgements section.¶

A.4. Since 'draft-reschke-webdav-property-datatypes-03'

Replaced domain names in examples according to RFC2606: "www.foo.com" by "example.org", "www.example.com" by "ns.example.org/standards/z39.50/standards/z39.50" and "www.w3.com/standards/z39.50" by "ns.example.org/standards/z39.50".¶

A.5. Since 'draft-reschke-webdav-property-datatypes-04'

Remove superfluous IP and copyright sections. Moved "Introduction" section to front.¶

A.6. Since 'draft-reschke-webdav-property-datatypes-05'

Added proposal for DAV:basicsearch operators for array-typed properties. Update all references.¶

A.7. Since 'draft-reschke-webdav-property-datatypes-06'

Reformat abstract. Remove property flags, displayname support and DASL extensions.¶

A.8. Since 'draft-reschke-webdav-property-datatypes-07'

Rewrite Editorial Note. Get rid of unnecessary sub section titles after removal of property flags and displayname support (no change tracking). Some typos fixed. Add and resolve issues "other-method-semantics", "1_clarify_scope", "7_discovery" and "a_remove_array_example". Removed unused reference to XML spec (no change tracking).

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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