RFC4316: Datatypes for Web Distributed Authoring and Versioning (WebDAV) Properties
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Related keywords:
(datatying)
(propfind)
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
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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".
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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.
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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 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">
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<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>
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<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" ?>
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<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
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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.
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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/
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RFC 4316 Datatypes for WebDAV Properties December 2005
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