Network Working Group J. F. Reschke
Internet Draft greenbytes
Expires: December 2002 June 2002
Datatypes for WebDAV properties
draft-reschke-webdav-property-datatypes-02
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
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This Internet-Draft will expire in December 2002.
Copyright Notice
Copyright (C) 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
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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/.
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Table of Contents
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . 3
1 Notational Conventions . . . . . . . . . . . . . . . . . . . . 4
2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
3 Overview of data types . . . . . . . . . . . . . . . . . . . . 6
4 Changes for PROPPATCH method . . . . . . . . . . . . . . . . . 7
4.1 Example for successful PROPPATCH . . . . . . . . . . . . . 7
4.2 Example for failed PROPPATCH . . . . . . . . . . . . . . . 8
4.3 Example for succesful PROPPATCH where type information was
not preserved . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5 Changes for PROPFIND method . . . . . . . . . . . . . . . . . . 11
5.1 Example for PROPFIND/prop . . . . . . . . . . . . . . . . . 11
6 Example: marshalling of array-typed properties . . . . . . . . 13
6.1 Setting of array-typed property . . . . . . . . . . . . . . 13
6.2 Getting an array-typed property . . . . . . . . . . . . . . 14
7 Compatibility Considerations . . . . . . . . . . . . . . . . . 16
8 Internationalization Considerations . . . . . . . . . . . . . . 17
9 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 18
10 Copyright . . . . . . . . . . . . . . . . . . . . . . . . . . 19
11 Intellectual Property . . . . . . . . . . . . . . . . . . . . 20
Normative References . . . . . . . . . . . . . . . . . . . . . . 21
Informative References . . . . . . . . . . . . . . . . . . . . . 21
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 21
A Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 22
A.1 Since 'draft-reschke-webdav-property-datatypes-00' . . . . 22
A.2 Since 'draft-reschke-webdav-property-datatypes-01' . . . . 22
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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
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 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.
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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 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
false
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
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http://www.foo.com/bar.html
HTTP/1.1 200 OK
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
t
>>Response
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HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
http://www.foo.com/bar.html
HTTP/1.1 422 Unprocessable Entity
Does not parse as xs:boolean
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
t
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>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
http://www.foo.com/bar.html
HTTP/1.1 200 OK
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; charset="utf-8"
Content-Length: xxxx
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
http://www.foo.com/bar.html
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text/html
1
HTTP/1.1 200 OK
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 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
http://www.w3.org/TR/SOAP
http://www.w3.org/TR/xmlschema-2
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>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
http://www.foo.com/bar.html
HTTP/1.1 200 OK
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
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>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
http://www.foo.com/bar.html
http://www.w3.org/TR/SOAP
http://www.w3.org/TR/xmlschema-2
HTTP/1.1 200 OK
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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.
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8 Internationalization Considerations
This proposal builds on [RFC2518], and inherits its
internationalizability.
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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.
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10 Copyright
To be supplied by the RFC Editor.
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11 Intellectual Property
To be supplied by the RFC Editor.
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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.R. and
Jensen, D., "HTTP Extensions for Distributed Authoring --
WEBDAV", RFC 2518, February 1999.
[XML] Bray, T., Paoli, J., Sperberg-McQueen, C. M., Maler, E.
and World Wide Web Consortium, "Extensible Markup Language
(XML) 1.0", W3C XML, February 1998.
[XS1] Thompson, H. S., Beech, D., Maloney, M., Mendelsohn, N.
and World Wide Web Consortium, "XML Schema Part 1:
Structures", W3C XS1, May 2001.
[XS2] Biron, P. V., Malhotra, A. and World Wide Web Consortium,
"XML Schema Part 2: Datatypes", W3C XS2, May 2001.
Informative References
[SOAP11] Box, D., Ehnebuske, D., Kakivaya, G., Layman, A.,
Mendelsohn, N., Nielsen, H. F., Thatte, S., Winer, D. and
World Wide Web Consortium, "Simple Object Access Protocol
1.1", W3C Note SOAP, May 2000.
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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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".
Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved.
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Acknowledgement
Funding for the RFC editor function is currently provided by the
Internet Society.
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