WEBDAV Working Group Y. Y. Goland, Microsoft
INTERNET-DRAFT E. J. Whitehead, Jr., U.C. Irvine
<draft-ietf-webdav-protocol-02> A. Faizi, Netscape
S. R Carter, Novell
D. Jensen, Novell
Expires March 8, 1998 September 3, 1997
Extensions for Distributed Authoring and Versioning
on the
World Wide Web -- WEBDAV
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Abstract
This Document specifies a set of methods and content-types
ancillary to HTTP/1.1 for the management of resource properties,
simple name space manipulation, simple resource locking
(collision avoidance) and resource version control.
Table of Contents
Abstract
1 Terminology
2 Data Model and Methods for DAV Properties
2.1 Introduction
2.1.1 The DAV Property
2.1.2 Existing Metadata Proposals
2.1.3 Properties and HTTP Headers
2.2 A Property Model for HTTP Resources
2.2.1 Overview
2.2.2 Property Namespace
2.3 Schemas
2.3.1 PropSchema XML Element
2.3.2 DTD XML Element
2.3.3 DefinedProps XML Element
2.3.4 PropEntries XML Element
2.3.5 Live XML Element
2.4 DAV Schema
2.4.1 DAV Property
2.4.2 Level XML Element
2.4.3 Prop XML element
2.4.4 PropLoc XML Attribute
2.4.5 Example
2.5 Property Identifiers
2.5.1 Problem Definition
2.6 Link XML Element
2.6.1 Problem Description
2.6.2 Solution Requirements
2.6.3 Link XML Element
2.6.4 Src XML Element
2.6.5 Dst XML Element
2.6.6 Example
2.7 Multi-Status Response
2.7.1 Problem Definition
2.7.2 Solution Requirements
2.7.3 Multi-Status Response
2.8 Properties and Methods
2.8.1 DELETE
2.8.2 GET
2.8.3 PROPPATCH
2.8.4 PUT
2.8.5 PROPFIND
3 A Proposal for Collections of Web Resources and Name Space
Operations
3.1 Observations on the HTTP Object Model
3.1.1 Collection Resources
3.1.2Creation and Retrieval of Collection Resources
3.1.3 Source Resources and Output Resources
3.2 MKCOL Method
3.2.1 Problem Description
3.2.2 Solution Requirements
3.2.3 Request
3.2.4 Response
3.2.5 Example
3.3 INDEX Method
3.3.1 Problem Description
3.3.2 Solution Requirements
3.3.3 The Request
3.3.4 The Response
3.3.5 Response Message Body
3.3.6 Example
3.4 Behavior of RFC 2068 Methods on Collections
3.4.1 GET, HEAD for Collections
3.4.2 POST for Collections
3.4.3 PUT for Collections
3.4.4 DELETE for Collections
3.5 COPY Method
3.5.1 Problem Description
3.5.2 Solution Requirements
3.5.3 The Request
3.5.4 The Response
3.5.5 Examples
3.6 MOVE Method
3.6.1 Problem Description
3.6.2 Solution Requirements
3.6.3 The Request
3.6.4 The Response
3.6.5 Examples
3.7 ADDREF Method
3.7.1 Problem Definition
3.7.2 Solution Requirements
3.7.3 The Request
3.8 DELREF Method
3.8.1 Problem Definition
3.8.2 Solution Requirements
3.8.3 The Request
3.9 PATCH Method
3.9.1 Problem Definition
3.9.2 Solution Requirements
3.9.3 The Request
3.9.4 application/XML elements for PATCH
3.9.5 The Response
3.9.6 Examples
3.10 Headers
3.10.1 Depth
3.10.2 Destination
3.10.3 Enforce-Live-Properties
3.10.4 Duplicate-Properties
3.10.5 Overwrite
3.10.6 Destroy Header
3.10.7 Mandatory header
3.10.8 Collection-Member Header
3.11 Links
3.11.1 Source Link Property Type
4 State Tokens
4.1 Overview
4.1.1 Problem Description
4.1.2 Solution Requirements
4.2 State Token Syntax
4.3 State Token Conditional Headers
4.3.1 If-State-Match
4.3.2 If-None-State-Match
4.4 State Token Header
4.5 E-Tags
5 Locking
5.1 Problem Description - Overview
5.1.1 Exclusive Vs. Shared Locks
5.1.2 Required Support
5.2 LOCK Method
5.2.1 Operation
5.2.2Effect of Locks on Properties and Containers
5.2.3 Locking Replicated Resources
5.2.4 Interaction with other Methods
5.2.5 Lock Compatibility Table
5.2.6 Status Codes
5.2.7 Example
5.2.8 Lock-Info Request Header
5.2.9 Owner Request Header
5.2.10 Time-Out Header
5.2.11 State-Token Header
5.3 Write Lock
5.4 Lock Tokens
5.4.1 Problem Description
5.4.2 Proposed Solution
5.4.3 Lock Token Definition
5.5 UNLOCK Method
5.5.1 Problem Definition
5.5.2 Example
5.6 Discovery Mechanisms
5.6.1 Lock Type Discovery
5.6.2 Active Lock Discovery
6 Version Control
7 Internationalization Support
8 Security Considerations
9 Acknowledgements
10 References
11 Authors' Addresses
1 Terminology
Collection - A resource that contains member resources.
Member Resource - a resource referred to by a collection. There
are two types of member resources: external and internal.
Internal Member Resource - the name given to a member resource of
a collection whose URI is relative to the URI of the collection.
External Member Resource - a member resource with an absolute URI
that is not relative to its parents URI.
Properties - A set of name/value pairs that contain descriptive
information about a resource.
Live Properties - Properties whose semantics and syntax are
enforced by the server. For example, a live "read-only" property
that is enforced by the server would disallow PUTs to the
associated resource.
Dead properties - Properties whose semantics and syntax are not
enforced by the server. A dead "read-only" property would not be
enforced by the server and thus would not be used by the server
as a reason to disallow a PUT on the associated resource.
2 Data Model and Methods for DAV Properties
2.1 Introduction
2.1.1 The DAV Property
Properties are pieces of data that describe the state of a
resource. Properties are data about data. The term property is
used within this specification to disambiguate the concept from
the overloaded terms "metadata" and "attribute".
Properties are used within distributed authoring environments to
provide for efficient discovery and management of resources. For
example, a 'subject' property might allow for the indexing of all
resources by their subject, and an 'author' property might allow
for the discovery of what authors have written which documents.
2.1.2 Existing Metadata Proposals
Properties have a long played an essential role in the
maintenance of large document repositories, and many current
proposals contain some notion of a property. These include PICS
[Miller et al., 1996], PICS-NG, the Rel/Rev draft [Maloney,
1996], Web Collections, XML [Bray, Sperberg-McQueen, 1997],
several proposals on representing relationships within HTML,
digital signature manifests (DCMF), and a position paper on Web
metadata architecture [Berners-Lee, 1997].
Some proposals come from a digital library perspective. These
include the Dublin Core [Weibel et al., 1995] metadata set and
the Warwick Framework [Lagoze, 1996], a container architecture
for different metadata schemas. The literature includes many
examples of metadata, including MARC [MARC, 1994], a
bibliographic metadata format, RFC 1807 [Lasher, Cohen, 1995], a
technical report bibliographic format employed by the Dienst
system, and the proceedings from the first IEEE Metadata
conference describe many community-specific metadata sets.
Participants of the 1996 Metadata II Workshop in Warwick, UK
[Lagoze, 1996], noted that, "new metadata sets will develop as
the networked infrastructure matures" and "different communities
will propose, design, and be responsible for different types of
metadata." These observations can be corroborated by noting that
many community-specific sets of metadata already exist, and there
is significant motivation for the development of new forms of
metadata as many communities increasingly make their data
available in digital form, requiring a metadata format to assist
data location and cataloging.
2.1.3 Properties and HTTP Headers
Properties already exist, in a limited sense, within HTTP through
the use of message headers. However, in distributed authoring
environments a relatively large number of properties are needed
to describe the state of a resource, and setting/returning them
all through HTTP headers is inefficient. Thus a mechanism is
needed which allows a principal to identify a set of properties
in which the principal is interested and to then set or retrieve
just those properties.
2.2 A Property Model for HTTP Resources
2.2.1 Overview
The DAV property model is based on name/value doubles. The name
of a property identifies the property's syntax and semantics, and
provides an address with which to refer to a property. The name
and value of a property is expressed as a well-formed XML
element, where the name of the property is the name of the XML
element, and the value of the property MUST be either blank, or a
well-formed XML element value.
2.2.2 Property Namespace
2.2.2.1 Problem Definition
The requirement is to be able to associate a value with a
property name on a resource and to be able to directly address
that value.
2.2.2.2 Solution Requirement
Ideally a property namespace should work well with extant
property implementations as well as database systems. The DAV
property namespace has been specified with the following two
facts in mind:
· Namespaces associated with flat file systems are ubiquitous.
· The majority of databases use a fixed schema mechanism.
The last point makes efficient implementation of hierarchical
properties difficult. Specifically, each property has a random
set of children; the best a relational database can do is provide
a table with name and value, where the value is a series of
indexes into other tables and each index represents a specific
value. However most RDBS do not provide for table pointers, only
index values. Such a system would have to be jury-rigged to
handle table pointers. In addition, indexing systems are
optimized for a small set of relatively large tables;
hierarchical property systems tend toward many properties, each
with different numbers and types of children, thus potentially
requiring a table for each child.
It would seem best to implement a flat property namespace,
inducing a natural isomorphism between DAV and most native file
systems. Adopting such a model will not restrict RDBS from taking
full advantage of their search facilities.
However, it seems that future trends might be toward hierarchical
properties. Therefore, DAV requirements [Slein et al.] stipulate
that the design of the flat property system MUST be such that it
will be possible to add true hierarchical properties later
without breaking downlevel clients. Specifically, a flat client
MUST be able to speak to a hierarchical server and a hierarchical
client MUST be able to speak to a flat server. Worst case either
way MUST be that the request fails.
2.2.2.3 Property Names
A property name identifies both the syntax and semantics of the
property's value. It is critical that property names do not
collide, e.g., two principals defining the same property name
with two different meanings.
The URI framework provides a mechanism to prevent namespace
collision and for varying degrees of administrative control.
Rather than reinvent these desirable features, DAV properties
make use of them by requiring that all DAV property names MUST be
URIs. Since a property is also an XML element, the name of the
XML element is a URI.
The property namespace is flat, that is, it is not possible to
string together a series of property names in order to refer to a
hierarchy of properties. Thus it is possible to refer to a
property B but not a property A/B, where is also a property
defined on the resource.
Finally, it is not possible to define the same property twice as
this would cause a collision in the resource's property
namespace.
2.3 Schemas
A schema is a group of property names and XML elements.
Schema discovery is used to determine if a system supports a
group of properties or XML elements. A property does not
necessarily contain sufficient information to identify any
schema(s) to which it may belong.
As with property names, schemas MUST use URIs as their names.
A resource declares its support for a schema by defining a
property whose name is the same as the schema's. The property
SHOULD contain the PropSchema XML element.
2.3.1 PropSchema XML Element
Name: http://www.ietf.org/standards/dav/PropSchema
Purpose: To provide information about properties
Schema: http://www.ietf.org/standards/dav/
Parent: Any
Values= [DTD] [DefinedProps]
Description:This property contains the definition of the schema.
This definition consists of two parts. A DTD element that
contains a DTD that declares all XML elements and DefinedProps
that defines any properties associated with the schema. As with
all XML it is possible to add extra XML elements. Therefore
schemas may define extra XML elements which are to be included
with their values.
2.3.2 DTD XML Element
Name: http://www.ietf.org/standards/dav/DTD
Purpose: To contain the DTD for XML elements associated with the
schema.
Schema: http://www.ietf.org/standards/dav/
Parent: Any
Values: XML Declaration statements
2.3.3 DefinedProps XML Element
Name: http://www.ietf.org/standards/dav/DefinedProps
Purpose: To contain a list of properties defined by the schema.
Schema: http://www.ietf.org/standards/dav/
Parent: Any
Values= 1*PropEntries
2.3.4 PropEntries XML Element
Name: http://www.ietf.org/standards/dav/PropEntries
Purpose: To contain the name of a defined property, the DTD of
its value, and its live/dead status.
Schema: http://www.ietf.org/standards/dav/
Parent: DefinedProps
Values= Prop [DTD] [Live]
Description:Prop contains the name of the property. The DTD
contains the DTD of the property's value. Live, if defined,
indicates that the property has semantics and syntax that are
enforced by the server.
2.3.5 Live XML Element
Name: http://www.ietf.org/standards/dav/Live
Purpose: If present this indicates the server MUST enforce the
syntax and semantics of the property.
Schema: http://www.ietf.org/standards/dav/
Parent: PropEntries
2.4 DAV Schema
The DAV Schema is specified as
http://www.ietf.org/standards/dav/. This schema is used to
indicate support for
· properties that may be defined on a resource and
· XML elements that may be returned in responses.
2.4.1 DAV Property
Name: http://www.ietf.org/standards/dav
Purpose: Defines support for the DAV schema and protocol.
Schema: http://www.ietf.org/standards/dav/
Values= PropSchema Level
Description:This property indicates that the resource supports
the DAV schema and protocol to the level indicated. THE VALUE IN
PROPSCHEMA IS TBD, WE NEED TO PROVIDE IT IN AN APPENDIX.
2.4.2 Level XML Element
Name: http://www.ietf.org/standards/dav/level
Purpose: To indicate the level of DAV compliance the resource
meets.
Schema: http://www.ietf.org/standards/dav/
Parent: DAV
Values= "1" | "2" | "3"
Description:A value of 1 for level indicates that the resource
supports the property and namespace sections of the DAV
specification. Level 2 indicates that the resource supports level
1 and the lock section of the specification, with a minimum
locking capability of the write lock. Level 3 indicates support
for levels 1 and 2 as well as support for the versioning section
of the DAV specification.
2.4.3 Prop XML element
Name: http://www.ietf.org/standards/dav/prop
Purpose: Contains properties related to a resource.
Schema: http://www.ietf.org/standards/dav/
Parent: Any
Values: XML Elements
Description:The Prop XML element is a generic container for
properties defined on resources. All elements inside Prop MUST
define properties related to the resource. No other elements may
be used inside of a Prop element.
2.4.4 PropLoc XML Attribute
Name: http://www.ietf.org/standards/dav/PropLoc
Purpose: To specify the location of the associated property.
Schema: http://www.ietf.org/standards/dav/
Values= URL
Description:This attribute is used with elements inside of Props
contained in responses to specify the URL of the property on the
associated resource. The PropLoc attribute MUST NOT be used in
requests.
2.4.5 Example
<?XML:Namespace href="http://www.ietf.org/standards/dav/"
AS="D"/>
<?XML:Namespace href="AIIM:Dublin:" AS="A"/>
<D:Prop>
<A:Author
D:PropLoc="http://www.foo.com/resource/props/Author">
Larry Masinter
</A:Author>
</D:Prop>
The previous specifies that the property author exists on some
unspecified resource and that the property can be directly
referenced at http://www.foo.com/resource/props/Author. The
resource upon which the property is defined must be determined
from context.
2.5 Property Identifiers
2.5.1 Problem Definition
DAV properties are resources and thus may have a URI where the
value of an instance of the property may be retrieved. This URI
is separate from the URI name of the property, which identifies
the syntax and semantics of the property, but which does not give
information on how to access the value of an instance of the
property.
A server is free to assign whatever URI it chooses to identify an
instance of a property defined on a resource. In fact, a server
is free not to reveal the URI of an instance of a particular
resource and instead require that the client access the property
through PROPFIND and PROPPATCH. However, many servers will want
to allow clients to directly manipulate properties. On these
servers, a client can discover the URI of an instance of a
property by performing a PROPFIND and examining the PropLoc
attribute, if returned, of each property.
2.6 Link XML Element
2.6.1 Problem Description
A mechanism is needed to associate resources with other
resources. These associations, known as links, consist of three
values, a type describing the nature of the association, the
source of the link, and the destination of the link. In the case
of annotation, neither the source nor the destination of a link
need be the resource upon which the link is recorded.
2.6.2 Solution Requirements
The association mechanism MUST make use of the DAV property
mechanism in order to make the existence of the associations
searchable.
2.6.3 Link XML Element
Name: http://www.ietf.org/standards/dav/link
Purpose: To identify a property as a link and to contain the
source and destination of that link.
Schema: http://www.ietf.org/standards/dav/
Values= 1*Src 1*Dst
Description:Link is used to provide the sources and destinations
of a link. The type of the property containing the Link XML
element provides the type of the link. Link is a multi-valued
element, so multiple Links may be used together to indicate
multiple links with the same type.
2.6.4 Src XML Element
Name: http://www.ietf.org/standards/dav/src
Purpose: To indicate the source of a link.
Schema: http://www.ietf.org/standards/dav/
Parent: http://www.ietf.org/standards/dav/link
Values= URI
2.6.5 Dst XML Element
Name: http://www.ietf.org/standards/dav/Dst
Purpose: To indicate the destination of a link
Schema: http://www.ietf.org/standards/dav/
Parent: http://www.ietf.org/standards/dav/link
Values= URI
2.6.6 Example
<?XML:Namespace
href = "http://www.ietf.org/standards/dav/" AS = "D"/>
<?XML:Namespace
href = "http://www.foocorp.com/Project/" AS = "F"/>
<D:Prop>
<Source>
<Link>
<F:ProjFiles>Source</F:ProjFiles>
<src>http://foo.bar/program</src>
<dst>http://foo.bar/src/main.c</dst>
</Link>
<Link>
<F:ProjFiles>Library</F:ProjFiles>
<src>http://foo.bar/program</src>
<dst>http://foo.bar/src/main.lib</dst>
</Link>
<Link>
<F:ProjFiles>Makefile</F:ProjFiles>
<src>http://foo.bar/program</src>
<dst>http://foo.bar/src/makefile</dst>
<Link>
</Source>
</D:Prop>
In this example the resource http://foo.bar/program has a source
property defined which contains three links. Each link contains
three elements, two of which, src and dst, are part of the DAV
schema defined in this document, and one which is defined by the
schema http://www.foocorp.com/project/ (Source, Library, and
Makefile). A client which only implements the elements in the DAV
spec will not understand the foocorp elements and will ignore
them, thus seeing the expected source and destination links. An
enhanced client may know about the foocorp elements and be able
to present the user with additional information about the links.
2.7 Multi-Status Response
2.7.1 Problem Definition
Some methods effect more than one resource. The effect of the
method on each of the scoped resources may be different, as such
a return format that can specify the effect of the method on each
resource is needed.
2.7.2 Solution Requirements
The solution must:
- communicate the status code and reason
- give the URI of the resource on which the method was invoked
- be consistent with other return body formats
-
2.7.3 Multi-Status Response
The default multi-status response body is an text/xml HTTP entity
that contains a single XML element called multiresponse, which
contains a set of XML elements called response, one for each 200,
300, 400, and 500 series status code generated during the method
invocation. 100 series status codes MUST NOT be recorded in a
response XML element.
2.7.3.1 MultiResponse
Name: http://www.ietf.org/standards/dav/multiresponse
Purpose: Contains multiple response messages.
Schema: http://www.ietf.org/standards/dav/
Parent: Any
Value: 1*Response [ResponseDescription]
Description:The ResponseDescription at the top level is used to
provide a general message describing the over arching nature of
the response. If this value is available an application MAY use
it instead of presenting the individual response descriptions
contain within the responses.
2.7.3.2 Response
Name: http://www.ietf.org/standards/dav/response
Purpose: Holds a single response
Schema: http://www.ietf.org/standards/dav/
Parent: Any
Value: (Prop | HREF) Status [ResponseDescription]
Description: Prop MUST contain one or more empty XML elements
representing the name of properties. Multiple properties may be
included if the same response applies to them all. If HREF is
used then the response refers to a problem with the referenced
resource, not a property.
2.7.3.3 Status
Name: http://www.ietf.org/standards/dav/status
Purpose: Holds a single HTTP status-line
Schema: http://www.ietf.org/standards/dav/
Parent: Response
Value: status-line ;status-line defined in [Fielding et al.,
1997]
2.7.3.4 ResponseDescription
Name:
http://www.ietf.org/standards/dav/ResponseDescription
Purpose: Contains a message that can be displayed to the user
explaining the nature of the response.
Schema: http://www.ietf.org/standards/dav/
Parent: Multiresponse and/or Response
Value: Any
Description: This XML element provides information suitable to
be presented to a user.
2.8 Properties and Methods
2.8.1 DELETE
As properties are resources, the deletion of a property causes
the same result as the deletion of any resource. It is worth
pointing out that the deletion of a property effects both direct
manipulation, that is by the property's URL, as well as indirect
discovery and manipulation, that is PROPPATCH and PROPFIND.
2.8.2 GET
A GET with a Request-URI that identifies a property returns the
name and value of that property. Accept types may be used to
specify the format of the return value, but all DAV compliant
servers MUST at minimum support a return type of text/xml. If
text/xml is used as the response format then it MUST return the
name and value of the property using the Prop XML element.
2.8.2.1 Example
The following example assumes that the property's URL, originally
generated by the server, was discovered by examining the proploc
XML attribute returned on a result from a FINDPROP.
GET /bar.html;prop=z39.50_authors HTTP/1.1
Host: foo.com
HTTP/1.1 200 OK
Content-Type: text/xml
Content-Length: xxxx
E-tag: "1234"
Last-Modified: xxxx
<?XML:Namespace
href = "http://www.ietf.org/standards/dav/" AS = "D"/>
<?XML:Namespace
href = "http://www.w3.com/standards/z39.50/"AS = "Z"/>
<D:prop>
<Z:Authors>
<Z:Author>Jane Doe</Z:Author>
<Z:Author>Joe Doe</Z:Author>
<Z:Author>Lots o'Doe</Z:Author>
</Z:Authors>
</D:prop>
2.8.3 PROPPATCH
The PROPPATCH method processes instructions specified in the
request body to create and/or remove properties defined on the
resource identified by Request-URI.
All DAV compliant servers MUST process instructions which are
specified using the PropertyUpdate, Create, and Remove XML
elements of the DAV schema. The request message body MUST
contain at least one PropertyUpdate XML element. Instruction
processing MUST occur in the order instructions are received
(i.e., from top to bottom), and MUST be performed atomically.
2.8.3.1 PropertyUpdate XML element
Name: http://www.ietf.org/standards/dav/PropertyUpdate
Purpose: To contain a request to alter the properties on a
resource.
Schema: http://www.ietf.org/standards/dav/
Parent: Any
Values= *(Create | Remove)
Description:This XML element is a container for the information
required to modify the properties on the resource. This XML
element is multi-valued.
2.8.3.2 Create XML element
Name: http://www.ietf.org/standards/dav/create
Purpose: To create the DAV properties specified inside the
Create XML element.
Schema: http://www.ietf.org/standards/dav/
Parent: http://www.ietf.org/standards/dav/PropertyUpdate
Values= Prop
Description:This XML element MUST contain only a Prop XML
element. The elements contained by Prop specify the name and
value of properties that are created on Request-URI. If a
property already exists then its value is replaced. The Prop XML
element MUST NOT contain a PropLoc XML attribute.
2.8.3.3 Remove XML element
Name: http://www.ietf.org/standards/dav/remove
Purpose: To remove the DAV properties specified inside the
Remove XML element.
Schema: http://www.ietf.org/standards/dav/
Parent: http://www.ietf.org/standards/dav/PropertyUpdate
Values= Prop
Description:Remove specifies that the properties specified in
Prop should be removed. Specifying the removal of a property that
does not exist is not an error. All the elements in Prop MUST be
empty, as only the names of properties to be removed are
required.
2.8.3.4 Response
The response MUST have a response body that contains a
multiresponse identifying the results for each property.
2.8.3.5 Response Codes
200 OK - The command succeeded. As there can be a mixture of
Create and Removes in a body, a 201 Create seems inappropriate.
403 Forbidden - The client, for reasons the server chooses not to
specify, can not alter one of the properties.
405 Conflict - The client has provided a value whose semantics
are not appropriate for the property. This includes trying to set
read only properties.
413 Request Entity Too Long - If a particular property is too
long to be recorded then a composite XML error will be returned
indicating the offending property.
417 Insufficient Space on Resource - The resource does not have
sufficient space to record the state of the resource after the
execution of this method.
418 Atomicity Failure - The command was not executed because of
an atomicity failure elsewhere the caused the entire command to
be aborted.
2.8.3.6 Example
PROPPATCH /bar.html HTTP/1.1
Host: www.foo.com
Content-Type: text/xml
Content-Length: xxxx
<?XML:Namespace
href = "http://www.ietf.org/standards/dav/" AS = "D"/>
<?XML:Namespace
href = "http://www.w3.com/standards/z39.50/" AS = "Z"/>
<D:PropertyUpdate>
<Create>
<prop>
<Z:authors>
<Z:Author>Jim Whitehead</Z:Author>
<Z:Author>Roy Fielding</Z:Author>
</Z:authors>
</Prop>
</Create>
<Remove>
<prop><Z:Copyright-Owner/></prop>
</Remove>
</D:PropertyUpdate>
HTTP/1.1 405 Conflict
Content-Type: text/xml
Content-Length: xxxxx
<?XML:Namespace
href="http://www.ietf.org/standards/dav/" AS = "D"/>
<?XML:Namespace
href="http://www.w3.com/standards/z39.50/" AS = "Z"/>
<D:MultiResponse>
<ResponseDescription> Copyright Owner can not be deleted or
altered.</ResponseDescription>
<Response>
<Prop><Z:authors/></Prop>
<Status>HTTP/1.1 418 Atomicity Failure</Status>
</Response>
<Response>
<Prop><Z:Copyright-Owner/></Prop>
<Status>HTTP/1.1 405 Conflict</Status>
</Response>
</D:MultiResponse>
2.8.4 PUT
A PUT is specified in order to control what is returned by a GET.
However a GET on a property always returns a predefined property
containment format. Therefore PUT can not be used if the Request-
URI refers to a property.
2.8.5 PROPFIND
The PROPFIND method retrieves properties defined on Request-URI.
The request message body is an XML document that MUST contain
only one PropFind XML element, which specifies the type of
property find action to be performed. The XML element contained
by PropFind specifies the type of action to be performed:
retrieve all property names and values (AllProp), retrieve only
specified property names and values (Prop), or retrieve only a
list of all property names (Propname). When a Prop XML element
is present, it specifies a list of the names of properties whose
name and value are to be returned. The Prop element, when used
within a FINDPROP request body MUST be empty.
The response is a text/xml message body that contains a
MultiResponse XML element which describes the results of the
attempts to retrieve the various properties. If a property was
successfully retrieved then its value MUST be returned in the
prop XML element. In the case of Allprop and Findprop, if a
principal does not have the right to know if a particular
property exists, an error MUST NOT be returned. The results of
this method SHOULD NOT be cached.
2.8.5.1 Propfind XML element
Name: http://www.ietf.org/standards/dav/Propfind
Purpose: To specify the set of matching properties
Schema: http://www.ietf.org/standards/dav/
Parent: Any
Values= (Prop | Allprop | Propname)
Description: Propfind is a container element for the exact
specification of a PROPFIND request.
2.8.5.2 Allprop
Name: http://www.ietf.org/standards/dav/Allprop
Purpose: To specify that all properties are to be returned
Schema: http://www.ietf.org/standards/dav/
Parent: Propfind
Description: Its presence in a PROPFIND request specifies the
name and value of all properties defined on the resource MUST be
returned.
2.8.5.3 Propname
Name: http://www.ietf.org/standards/dav/Propname
Purpose: To specify that the names of all properties defined on
the resource are to be returned.
Schema: http://www.ietf.org/standards/dav/
Parent: Propfind
Description: Its presence in a PROPFIND request specifies the
name of all properties defined on the resource MUST be returned.
2.8.5.4 PropFindResult XML element
Name: http://www.ietf.org/standards/dav/PropFindResult
Purpose: To contain the results of a SEARCH request
Schema: http://www.ietf.org/standards/dav/
Parent: Any
Values: Prop
2.8.5.5 Example 1 - Prop
PROPFIND /container/ HTTP/1.1
Host: www.foo.bar
Content-Length: xxxx
Content-Type: text/xml
<?XML:Namespace href =
"http://www.ietf.org/standards/dav/" AS = "G"/>
<?XML:Namespace href =
"http://www.foo.bar/boxschema/" AS = "B"/>
<G:PROPFIND>
<prop>
<B:bigbox>
<B:author>
<B:DingALing>
<B:Random>
</prop>
</G:PROPFIND>
HTTP/1.1 207 Partial Success
Content-Type: text/xml
Content-Length: xxxxx
<?XML:Namespace
href ="http://www.ietf.org/standards/dav/" AS = "S">
<?XML:Namespace href = "http://www.foo.bar/boxschema" AS = R">
<D:MultiResponse>
<ResponseDescription> There has been an access violation
error. </ResponseDescription>
<Response>
<Prop>
<R:bigbox D:Proploc="http://prop.com/BoxType">
<BoxType>Box type A</BoxType>
</R:bigbox>
<R:author D:Proploc="http://prop.com/Author">
<Name>J.J. Dingleheimerschmidt</Name>
</R:author>
</Prop>
<Status>HTTP/1.1 200 Success</Status>
</Response>
<Response>
<Prop><R:DingALing/><R:Random/></>
<Status>HTTP/1.1 403 Forbidden</Status>
<ResponseDescription> The user does not have access to
the DingALink property. </ResponseDescription>
</Response>
</D:MultiResponse>
The result will return all properties on the container. In this
case only two properties were found. The principal did not have
sufficient access rights to see the third and fourth properties
so an error was returned.
2.8.5.6 Example 2 - Allprop
PROPFIND /container/ HTTP/1.1
Host: www.foo.bar
Content-Length: xxxx
Content-Type: text/xml
<?XML:Namespace href =
"http://www.ietf.org/standards/dav/" AS = "G"/>
<G:PROPFIND>
<Allprop/>
</G:PROPFIND>
HTTP/1.1 200 Success
Content-Type: text/xml
Content-Length: xxxxx
<?XML:Namespace href =
"http://www.ietf.org/standards/dav/" As = "S">
<?XML:Namespace href = "http://www.foo.bar/boxschema" AS = R">
<S:MultiResponse>
<Prop>
<R:bigbox D:Proploc="http://prop.com/BigBox">
<BoxType>Box type A</BoxType>
</R:bigbox>
<R:author D:Proploc="http://prop.com/Author">
<Name>Hadrian</Name>
</R:author>
</Prop>
<Status>HTTP/1.1 200 Success</Status>
</S:MultiResponse>
This particular client only had the right to see two properties,
BoxType and Author. No error is returned for the remaining
properties, as the client does not even have sufficient rights to
know they exist. If the client did have the right to know they
existed but did not have the right to see their value, a 201
Partial Success with a multiresponse, as used in the previous
example, would have been returned.
2.8.5.7 Example 3 - Propname
PROPFIND /container/ HTTP/1.1
Host: www.foo.bar
Content-Length: xxxx
Content-Type: text/xml
<?XML:Namespace
href = "http://www.ietf.org/standards/dav/" AS = "G"/>
<G:PROPFIND>
<Propname/>
</G:PROPFIND>
HTTP/1.1 200 Success
Content-Type: text/xml
Content-Length: xxxxx
<?XML:Namespace
href = "http://www.ietf.org/standards/dav/" As = "S">
<?XML:Namespace
href = "http://www.foo.bar/boxschema" AS = "R">
<S:MultiResponse>
<Prop>
<R:bigbox D:Proploc="http://prop.com/BigBox"/>
<R:author D:Proploc="http://prop.com/Author"/>
<R:DingALing/>
<R:Random/>
</Prop>
<Status>HTTP/1.1 200 Success</Status>
</S:MultiResponse>
In this case only two of the properties have direct URLs
available, while the other two properties can only be referenced
via PROPFIND and PROPPATCH.
3 A Proposal for Collections of Web Resources and Name Space
Operations
3.1 Observations on the HTTP Object Model
As a prerequisite for specification of collections and name space
operations for the Web, a model for collection resources and for
namespace topology must be given. This section describes a new
type of Web resource, the collection resource, and provides a
model for discussing the relationship between the resources that
are generated as the result of a data-producing process, and the
source resources that describe the process.
3.1.1 Collection Resources
A collection is a Web resource type whose primary state is a set
of URIs and associated values that are recorded as properties on
the resource. The URIs identify resources that are members of
the collection. The values associated with each URI include
information such as the Last Modified Date, Entity Tag, Creation
Date, Content Type, Display Name, and whether the member is a
collection.
A member of a collection is either an internal member resource,
which MUST have a URI that is relative to the base URI of the
collection, or an external member resource, which has a URI which
is not relative to the base URI of the collection. External
member resources are further subdivided into propagate members,
which have recursive method invocations propagated to them, and
no-propagate members, which do not.
A collection resource may be viewed and used as a compound
resource in which the collection is a container for a group of
related resources that, together, form a larger logical unit.
For example, a collection of HTML resources where each resource
is the chapter of a book can be viewed as a compound resource
representing the entire book.
Some methods, when invoked on a collection, affect the entire
collection. For example, it is possible to copy an entire
collection and its contents with just a single copy method
request. The model for performing these operations is a tree
traversal. The method is invoked on the collection, which then
performs the method on itself before propagating the method to
all its internal members and propagate external members. If
these are non-collection resources, the request method is
processed. However, if the request is propagated to another
collection, then the propagation begins again. This sequence of
actions causes the method to be propagated as a tree traversal of
the members of the collections. It is incumbent upon the client
to perform any locking operation on the collection or subordinate
members that it deems necessary in order to maintain state
consistency during the execution of such methods.
3.1.2 Creation and Retrieval of Collection Resources
Since the existing HTTP methods for creating (PUT, POST) and
retrieving (GET) a resource were defined for non-collection
resources, it is not surprising that the semantics of these
methods do not transfer well to collections. For example, the PUT
method is defined to store the request entity under the Request-
URI. While a description format for a collection can readily be
constructed that could be used with PUT, the implications of
sending such a description to the server are undesirable. For
example, if a description of a collection that omitted some
existing resources were PUT to a server, this might be
interpreted as a command to remove those members. This would
extend PUT to perform DELETE functionality, which is undesirable
since it changes the semantics of PUT, and makes it difficult to
control DELETE functionality with an access control scheme based
on methods.
While the POST method is sufficiently open-ended that a "create a
collection" POST command could be constructed, this is
undesirable because it would be difficult to provide separate
access control for collection creation and other uses of POST if
they both use the same method.
The GET method when applied to collections is also problematic.
While it might seem desirable to have GET return a listing of the
members of a collection, this is foiled by the existence of the
"index.html" de-facto standard namespace redirection, in which a
GET request on a collection is automatically redirected to the
index.html resource.
Because of the difficulty of reusing some existing HTTP/1.1
methods for collections, two new resource creation/retrieval
methods are needed. This specification introduces the MKCOL
method for creating collection resources, and the INDEX method
for retrieving the contents of a collection.
The exact definition of the behavior of GET and PUT on
collections is defined later in this draft.
3.1.3 Source Resources and Output Resources
For many resources, the entity returned by GET exactly matches
the persistent state of the resource, for example, a GIF file
stored on a disk. For this simple case, the URL at which a
resource is accessed is identical to the URL at which the source
(the persistent state) of the resource is accessed. This is also
the case for HTML source files that are not processed by the
server prior to transmission.
However, HTML files can sometimes be processed by the server
before being transmitted as a return entity body. Server-side-
include directives within an HTML file instruct a server to
replace the directive with another value, such as the current
date. In this case, what is returned by GET (HTML plus date)
differs from the persistent state of the resource (HTML plus
directive). Typically there is no way to access the HTML file
containing the unprocessed directive.
Sometimes the entity returned by GET is the output of a data-
producing process that is described by one or more source
resources (that may not even have a location in the URL
namespace). A single data-producing process may dynamically
generate the state of a potentially large number of output
resources. An example of this is a CGI script that describes a
"finger" gateway process that maps part of the namespace of a
server into finger requests, such as
http://www.foo.bar.org/finger_gateway/user@host.
In the absence of distributed authoring capability, the fact that
the source resource(s) for server generated output do not have a
mapping to the URI namespace is not a problem, and has desirable
security benefits. However, if remote editing of the source
resource(s) is desired, they should be given a location in the
URI namespace. This source location should not be one of the
locations at which the generated output is retrievable, since in
general it is impossible for the server to differentiate requests
for source resources from requests for process output resources.
There is often a many-to-many relationship between source
resources and output resources. For DAV compliant servers all
output resources which have a single source resource (and that
source resource has a URI), the URI of the source resource SHOULD
be stored in a single link on the output resource with type
http://www.ietf.org/standards/dav/link/Source. Note that by
storing the source URI in links on the output resources, the
burden of discovering the source is placed on the authoring
client.
In the general case, a large number of source resources can
comprise a data-producing process that generates many output
resources, creating a many-to-many relationship between output
resources and source resources. If each output resource had links
back to every source resource in the data-producing process,
there can be a potentially large number of such links. Due to the
potentially large number of links, and the lack of a policy for
ordering access to multiple sources, explicit storage of source
relationships is limited to cases with only a single source
resource.
3.2 MKCOL Method
3.2.1 Problem Description
The client needs a way to create a collection.
3.2.2 Solution Requirements
The solution:
- Must ensure that a collection has been made (i.e. that it
responds to the INDEX method) as opposed to a non-collection
resource. If a collection could not be made, it must indicate a
failure to the principal.
- The server MAY, if necessary, create any intermediate
collections so that the underlying storage medium is self-
consistent.
-
3.2.3 Request
The MKCOL method creates a new collection resource at the
location specified by the Request-URI. If the Request-URI exists
then MKCOL must fail.
During MKCOL processing, a server MAY add the Request-URI to one
or more collections within the servers controlled namespace.
3.2.3.1 MKCOL Without Request Body
When MKCOL is invoked without a request body then the collection
created has no members.
3.2.3.2 MKCOL With Request Body
A MKCOL request message MAY contain a message body. The behavior
of a MKCOL request when the body is present is limited to
creating collections, members of a collection, bodies of members
and properties on the collections or members. If the server
receives a MKCOL request entity type it does not support or
understand it MUST respond with a 415 (Unsupported Media Type)
status code.
3.2.3.3 Creating Multiple Collections
The server MAY create intermediate collections if they do not
already exist. For example, if the collection http://server/a/
already exists in the servers namespace, then while performing a
MKCOL to create http://server/a/b/c/ the server may also create a
collection at http://server/a/b/.
3.2.4 Response
Responses from a MKCOL request are not cacheable, since MKCOL has
non-idempotent semantics.
201 (Created) - The structured resource was created in its
entirety.
403 (Forbidden) - The server does not allow the creation of
collections at the given location in its namespace.
415 (Unsupported Media Type)- The server does not support the
request type of the body.
416 (Unprocessable Entity) - A new status code. The server
understands the content type of the request entity, but was
unable to process the contained instructions.
3.2.5 Example
This example creates a container collection called
/webdisc/xfiles/ on the server www.server.org.
MKCOL /webdisc/xfiles/ HTTP/1.1
Host: www.server.org
HTTP/1.1 201 Created
3.3 INDEX Method
3.3.1 Problem Description
A mechanism is needed to discover if a resource is a collection
and if so, list its members.
3.3.2 Solution Requirements
The solution:
- must allow a client to discover the members of a collection
- must always provide a machine-readable description of the
membership of a collection
-
3.3.3 The Request
The INDEX method returns a machine-readable representation of the
membership of the resource at the Request-URI. For a collection,
INDEX MUST return a machine-readable list of its members. For
other resources, the information returned by INDEX is undefined,
and MAY vary. The request message body of an INDEX request
SHOULD be ignored.
The Depth header can be used to indicate how much of a result can
be generated for the response. The specific values allowed for
the depth header when used with the INDEX method are 1 and
infinity. The 1 value indicates that the internal and external
member resources should be reported in the result, infinity
indicates that all internal and external member resources and all
their descendants should be in the result. If the Depth header is
not given, then 1 is assumed. Servers MUST honor a depth of 1.
Servers MAY honor infinity. If the server does not support the
value of the depth header then a 412 (Precondition failed) MUST
be returned.
3.3.4 The Response
200 (OK) - The server MUST send an application/xml response
entity which describes the collection.
404 (Not Found) - Same behavior as HTTP 1.1. The server never had
the resource, or the server permanently deleted the resource and
has no knowledge that it ever existed. This error code implies
that, essentially, the server has no information about the
Request URI.
3.3.5 Response Message Body
The default INDEX response for a resource is an application/xml
HTTP entity (i.e., an Extensible Markup Language (XML) document)
that contains a single XML element called collectionresource
which describes the collection, and a set of XML elements called
memberesource which describe the members of the collection.
The response from INDEX is cacheable, and SHOULD be accompanied
by an ETag header (see section 13.3.4 of RFC 2068). If GET and
INDEX return different entities for the same resource state, they
MUST return different entity tags.
The server MUST transmit the following XML elements for each
member resource of a collection: Ref, IsCollection, Content-Type,
External. The server MUST transmit the following XML elements if
it can generate any meaningful values for them: Creation-Date,
Last-Modified, DisplayName, Content-Language. The server SHOULD
transmit Etag XML elements for each member (see section 13.3.4 of
RFC 2068).
The value of content-type, last-modified, and etag XML elements
MUST be identical to the value of the response header field of
the same name in the HTTP/1.1 specification. Since the HTTP/1.1
header fields are described in terms of the on-the-wire entity,
the values presented by INDEX are those that would be generated
if the resource was accessed using the GET method without content
negotiation.
3.3.5.1 CollectionResource
Name: http://www.ietf.org/standards/dav/collectionresource
Purpose: Describes a collection
Schema: http://www.ietf.org/standards/dav/
Parent: <XML>
Value: MemberResource
3.3.5.2 MemberResource
Name: http://www.ietf.org/standards/dav/memberresource
Purpose: Describes a member of a collection
Schema: http://www.ietf.org/standards/dav/
Parent: CollectionResource
Value: Ref, IsCollection, Content-Type, External, Creation-
Date, Last-Modified, ETag, DisplayName (other XML elements MAY
also be present)
3.3.5.3 Ref
See XML definition.
3.3.5.4 IsCollection
Name: http://www.ietf.org/standards/dav/iscollection
Purpose: This is a boolean value which is set to "true" if the
entry is a collection
Schema: http://www.ietf.org/standards/dav/
Parent: MemberResource
Value: ("true" | "false")
3.3.5.5 Content-Type
Name: http://www.ietf.org/standards/dav/content-type
Purpose: The content-type of the member resource.
Schema: http://www.ietf.org/standards/dav/
Parent: MemberResource
Value: media-type ; defined in Section 3.7 of [Fielding et
al., 1997]
If no meaningful content-type can be generated, then an empty
value MUST be given.
3.3.5.6 External
Name: http://www.ietf.org/standards/dav/external
Purpose: If present, this element indicates the resource is an
external member of the collection. If the value is "propagate,"
it is a propagate member, if the value is "no-propagate," it is a
no-propagate member.
Schema: http://www.ietf.org/standards/dav/
Parent: MemberResource
Value: ("propagate" | "no-propagate")
3.3.5.7 Creation-Date
Name: http://www.ietf.org/standards/dav/creation-date
Purpose: The date the resource was created.
Schema: http://www.ietf.org/standards/dav/
Parent: MemberResource
Value: The date MUST be given in RFC 1123 format (rfc-1123
production, defined in section 3.3.1 of [Fielding et al., 1997]
3.3.5.8 Last-Modified
Name: http://www.ietf.org/standards/dav/last-modified
Purpose: The date the resource was last modified.
Schema: http://www.ietf.org/standards/dav/
Parent: MemberResource
Value: The date MUST be given in RFC 1123 format (rfc-1123
production, defined in section 3.3.1 of [Fielding et al., 1997]
3.3.5.9 ETag
Name: http://www.ietf.org/standards/dav/etag
Purpose: The entity tag of the resource.
Schema: http://www.ietf.org/standards/dav/
Parent: MemberResource
Value: entity-tag ; defined in Section 3.11 of [Fielding et
al., 1997]
3.3.5.10 DisplayName
Name: http://www.ietf.org/standards/dav/displayname
Purpose: A name for the resource that is suitable for
presentation to a person
Schema: http://www.ietf.org/standards/dav/
Parent: MemberResource
Value: Any valid XML character data (from XML specification)
3.3.5.11 Content-Language
Name: http://www.ietf.org/standards/dav/content-language
Purpose: Describes the natural language(s) of the intended
audience for the resource.
Schema: http://www.ietf.org.standards/dav/
Parent: MemberResource
Value: 1#language-tag ;language-tag is defined in section
14.13 of RFC 2068
3.3.6 Example
INDEX /user/yarong/dav_drafts/ HTTP/1.1
Host: www.microsoft.com
Depth: 1
HTTP/1.1 200 OK
Content-Type: application/xml
Content-Length: xxx
Last-Modified: xxx
ETag: "fooyyybar"
<XML>
<XML:Namespace><Ref>http://www.ietf.org/standards/dav/</><As
>D</></>
<D:CollectionResource>
<MemberResource>
<XML:Ref>namespace.doc</>
<IsCollection>false</>
<Content-Type>application/msword</>
<External>false</>
<Creation-Date>Thu, 20 Mar 1997 23:05:25 GMT</>
<Last-Modified>Fri, 22 Aug 1997 18:22:56 GMT</>
<Etag>8675309</>
<DisplayName>WebDAV Name Space Operations Draft</>
<Content-Language>en</>
</> </>
</>
This example shows the result of the INDEX method applied to the
collection resource
http://www.microsoft.com/er/yarong/dav_drafts/. It returns a
response body in XML format, which gives information about the
containers sole member,
http://www.microsoft.com/users/yarong/dav_drafts/namespace.doc.
3.4 Behavior of RFC 2068 Methods on Collections
With the introduction of the collection resource type to the HTTP
object model, it is necessary to define the behavior of the
existing methods (defined in RFC 2068) when invoked on a
collection resource to avoid ambiguity. While some methods, such
as OPTIONS and TRACE behave identically when applied to
collections, GET, HEAD, POST, PUT, and DELETE require some
additional explanation.
3.4.1 GET, HEAD for Collections
The semantics of GET are unchanged when applied to a collection,
since GET is defined as, "retrieve whatever information (in the
form of an entity) is identified by the Request-URI" [Fielding et
al., 1997]. GET when applied to a collection MAY return the
contents of an "index.html" resource, a human-readable view of
the contents of the collection, or something else altogether, and
hence it is possible the result of a GET on a collection will
bear no correlation to the state of the collection.
Similarly, since the definition of HEAD is a GET without a
response message body, the semantics of HEAD do not require any
modification when applied to collection resources.
3.4.2 POST for Collections
Since by definition the actual function performed by POST is
determined by the server and often depends on the particular
resource, the behavior of POST when applied to collections cannot
be modified because it is largely undefined. Thus the semantics
of POST do not require any modification when applied to a
collection.
3.4.3 PUT for Collections
In HTTP/1.1, PUT stores the request entity under the Request-URI,
and hence its semantics are limited to non-collection resources.
If a PUT is invoked on a collection resource it MUST fail.
When the PUT operation creates a new non-collection resource, a
server MAY add that resources URI to one or more collections
within the servers controlled namespace.
3.4.4 DELETE for Collections
When DELETE is applied to a collection resource, all internal
members MUST be recursively deleted. The dav:link/propagate
external members MUST be deleted and their links must be removed.
dav:link/nopropagate external members MUST have only their link
removed; the resources MUST not be deleted.
The Depth header does not apply to the DELETE method. It cannot
be used to limit the extent of the operation. If it is present it
MUST be ignored.
When applied to any resource, the DELETE method deletes all
properties on the Request-URI.
During DELETE processing, a server MAY remove the URI of the
deleted resource(s) from collections within its controlled
namespace.
3.4.4.1 New Response Codes for DELETE
207 (Partial Success) Only some of the member resources were
deleted. The response entity will describe any errors.
500 (Server Error) The resource was in such a state that it could
not be deleted. The response entity will describe reason for the
error.
3.5 COPY Method
3.5.1 Problem Description
Currently, in order to create a copy of a resource, the client
must GET an entity and then PUT that entity to the desired
destination. This requires (1) an entity to be transmitted to and
from the server and (2) that the resource be expressible as an
entity with complete fidelity. This is problematic because of
the network traffic involved in making a copy, and because there
is often no way to fully express a resource as an entity without
a loss of fidelity.
3.5.2 Solution Requirements
The solution:
- MUST allow a principal to create a copy of a resource
without having to transmit the resource to and from the server.
3.5.3 The Request
The COPY method creates a duplicate of the source resource, given
by the Request-URI, in the destination resource, given by the
Destination header. The Destination header MUST be present. The
exact behavior of the COPY method depends on the type of the
source resource.
3.5.3.1 COPY for HTTP/1.1 resources
When the source resource is not a collection, and is not a
property, the body of the destination resource MUST be octet-for-
octet identical to the body of the source resource. Alterations
to the destination resource do not modify the source resource.
Alterations to the source resource do not modify the destination
resource. Thus, all copies are performed "by-value".
If the Duplicate-Properties header is "false," then properties
SHOULD NOT be copied to the destination resource. If the
Duplicate-Properties header is "false" and the Enforce-Live-
Properties header is also present, the request MUST fail with a
412 (Precondition Failed) status code. [Ed. Note: what if
resource to be copied has no properties, and no properties are
explicitly named in the header?]
All properties on a source resource SHOULD be duplicated on the
destination resource following the definition for copying
properties.
3.5.3.2 COPY for Properties
Live properties SHOULD be duplicated as identically behaving live
properties at the destination resource. Since they are live
properties, the server determines the syntax and semantics (hence
value) of these properties. Properties named by the Enforce-
Live-
Properties header MUST be live on the destination resource, or
the method MUST fail. If a property is not named by Enforce-
Live-
Properties and cannot be copied live, then its value MUST be
duplicated in an identically named, dead resource on the
destination resource.
For every dead property defined on the source resource, there
SHOULD be an octet-for-octet identical dead property on the
destination resource.
3.5.3.3 COPY for Collections
The Depth and Overwrite headers govern the behavior of COPY for
collections.
When performing a recursive copy, all HTTP/1.1 request headers
are duplicated on the propagated method request except for the
precondition headers If-Modified-Since, If-Match, If-None-Match,
If-Range, If-Unmodified-Since, which should only be applied to
the Request-URI in order to determine if the operation should be
performed. The Destination header MUST be rewritten to preserve
the membership of the destination collection, i.e., by appending
the relative URI of the member to the URI of the destination
collection.
A Depth of "0" indicates the collection MUST duplicate all of its
external members in a new collection at the Destination. Since
the COPY method is not propagated to its members, no internal
member resource is duplicated.
A Depth of "1" indicates the collection MUST propagate the COPY
to all internal, non-collection members. If the Overwrite header
is "true" the COPY method duplicates all of its external members
in a new collection at the Destination. If the Overwrite header
is "false" and the destination resource is a collection, the COPY
method does not duplicate its external members, but is propagated
to all internal, non-collection members.
A Depth of "infinity" indicates the collection MUST propagate the
COPY method to all internal members. If the Overwrite header is
"true," the COPY method MUST duplicate all of its external
members in a new collection at the Destination. If the Overwrite
header is "false" and the destination resource is a collection,
then the COPY method does not duplicate its external members, but
is propagated to all internal members.
3.5.3.4 Type Interactions
If the destination resource identifies a property and the source
resource is not a property, then the copy SHOULD fail.
If the destination resource identifies a collection and the
Overwrite header is "true," prior to performing the copy, the
server MUST perform a DELETE operation on the collection.
3.5.4 The Response
200 (OK) The source resource was successfully copied to a pre-
existing destination resource.
201 (Created) The source resource was successfully copied. The
copy operation resulted in the creation of a new resource.
207 (Partial Success) Only some of the member resources were
copied. The return entity body describes the status code for each
resource.
412 (Precondition Failed) This status code MUST be returned if
the server was unable to maintain the liveness of the properties
listed in the Enforce-Live-Properties header, or if the Overwrite
header is false, and the state of the destination resource is
non-
null.
500 (Server Error) The resource was in such a state that it could
not be copied. This may occur if the Destination header indicated
an external (from the point of view of the server) resource and
the server has no capability to copy to an external resource.
502 (Bad Gateway) - This may occur when copying to external
resources and the destination server refused to accept the
resource.
3.5.5 Examples
3.5.5.1 Overwrite Example
This example shows resource
http://www.ics.uci.edu/~fielding/index.html being copied to the
location http://www.ics.uci.edu/users/f/fielding/index.html. The
contents of the destination resource were overwritten, if non-
null.
COPY /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination:
http://www.ics.uci.edu/users/f/fielding/index.html
Overwrite: "true"
HTTP/1.1 200 OK
3.5.5.2 No Overwrite Example
The following example shows the same copy operation being
performed, except with the Overwrite header set to "false." A
response of 412, Precondition Failed, is returned because the
destination resource has a non-null state.
COPY /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination:
http://www.ics.uci.edu/users/f/fielding/index.html
HTTP/1.1 412 Precondition Failed
3.6 MOVE Method
3.6.1 Problem Description
The move operation on a resource is the logical equivalent of a
copy followed by a delete.
In HTTP 1.1, the procedure could be performed in several steps.
First, the client could issue a GET to retrieve a representation
of a resource, issue a DELETE to remove the resource from the
server, then use PUT to place the resource on the server with a
new URI. As is the case for COPY - because of the network traffic
involved in making a move, and because there is often no way to
fully express a resource as an entity without a loss of fidelity
- server move functionality is preferable.
With a DAV server, a principal may accomplish this task by
issuing a COPY and then DELETE. Network load decreases, but the
server load may still be significant because the server must
create a duplicate resource. Were a server to know beforehand
that a principal intended to perform COPY and DELETE operations
in succession, it could avoid the creation of a duplicate
resource.
3.6.2 Solution Requirements
The solution:
- Must prevent the unneeded transfer of entity bodies from and
to the server.
- Must prevent the unneeded creation of copies by the server.
3.6.3 The Request
The MOVE method is defined as the logical equivalent of a COPY
followed by a DELETE of the source resource, performed
atomically.
3.6.4 The Response
200 (OK) - The resource was moved. A successful response must
contain the Content-Location header, set equal to the URI in
source. This lets caches properly flush any cached entries for
the source. Unfortunately the Content-Location header only allows
a single value so it is not possible for caches unfamiliar with
the MOVE method to properly clear their caches.
207 (Partial Success) Only some of the member resources were
moved. The return entity body will give the status code for each
resource.
412 (Precondition Failed) This status code MUST be returned if
the server was unable to maintain the liveness of the properties
listed in the Enforce-Live-Properties header, or if the Overwrite
header is false, and the state of the destination resource is
non-
null.
501 (Not Implemented) - This may occur if the Destination header
specifies a resource which is outside its domain of control
(e.g., stored on another server) resource and the server either
refuses or is incapable of moving to an external resource.
502 (Bad Gateway) - This may occur when moving to external
resources and the destination server refused to accept the
resource.
3.6.5 Examples
3.6.5.1 Overwrite Example
This example shows resource
http://www.ics.uci.edu/~fielding/index.html being moved to the
location http://www.ics.uci.edu/users/f/fielding/index.html. The
contents of the destination resource were overwritten, if non-
null.
MOVE /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination:
http://www.ics.uci.edu/users/f/fielding/index.html
Overwrite: true
HTTP/1.1 200 OK
Content-Location:
http://www.ics.uci.edu/users/f/fielding/index.html
3.7 ADDREF Method
3.7.1 Problem Definition
There needs to be a way to add an external member to a
collection.
3.7.2 Solution Requirements
The solution must:
- allow access control
- allow referencing to URIs of external members
- not require a body
3.7.3 The Request
The ADDREF method adds the URI specified in the Collection-Member
header as an external member to the collection specified by the
Request-URI. The value in the Collection-Member header MUST be an
absolute URI meeting the requirements of an external member URI.
The propagation type of the external URI is specified in the
Collection-Member Header.
3.8 DELREF Method
3.8.1 Problem Definition
There needs to be a way to remove an external member from a
collection.
3.8.2 Solution Requirements
The solution must:
- allow access control
- allow referencing to URIs of external members
- not require a body
3.8.3 The Request
The DELREF method removes the URI specified in the Collection-
Member header from the collection specified by the Request-URI.
3.9 PATCH Method
3.9.1 Problem Definition
At present, if a principal wishes to modify a resource, they must
issue a GET against the resource, modify their local copy of the
resource, and then issue a PUT to place the modified resource on
the server. This procedure is inefficient because the entire
entity for a resource must be transmitted to and from the server
in order to make even small changes. Ideally, the update entity
transmitted to the server should be proportional in size to the
modifications.
3.9.2 Solution Requirements
The solution must:
- allow partial modification of a resource without having to
transmit the entire modified resource
- allow byte-range patching
- allows extensions so that patches can be done beyond simple
byte-range patching
- allow ranges to be deleted, inserted, and replaced
3.9.3 The Request
The PATCH method contains a list of differences between the
original version of the resource identified by the Request-URI
and the desired content of the resource after the PATCH action
has been applied. The list of differences is in a format defined
by the media type of the entity (e.g., "application/diff") and
must include sufficient information to allow the server to
convert the original version of the resource to the desired
version.
Since the semantics of PATCH are non-idempotent, responses to
this method are not cacheable.
If the request appears (at least initially) to be acceptable, the
server MUST transmit an interim 100 response message after
receiving the empty line terminating the request headers and
continue processing the request.
While server support for PATCH is optional, if a server does
support PATCH, it MUST support at least the application/xml diff
format defined below. Support for the VTML difference format
[VTML] is recommended, but not required.
3.9.4 application/XML elements for PATCH
The resourceupdate XML elementXML element contains a set of XML
sub-entities that describe modification operations. The name and
meaning of these XML elements is given below. Processing of these
directives MUST be performed in the order encountered within the
XML document. A directive operates on the resource as modified
by all previous directives (executed in sequential order).
3.9.4.1 ResourceUpdate
Name: http://www.ietf.org/standards/dav/patch/resourceupdate
Purpose: Contains an ordered set of changes to a non-collection,
non-property resource.
Schema: http://www.ietf.org/standards/dav/patch/
Parent: <XML>
Value: *(Insert | Delete | Replace)
3.9.4.2 Insert
Name: http://www.ietf.org/standards/dav/patch/insert
Purpose: Insert the XML elementXML elements contents starting
exactly at the specified octet.
Schema: http://www.ietf.org/standards/dav/patch/
Parent: ResourceUpdate
Value: The insert XML elementXML element MUST contain an octet
XML elementXML element that specifies an octet position within
the body of a resource. A value of "end" specifies the end of
the resource. The body of the insert XML elementXML element
contains the octets to be inserted.
3.9.4.3 Delete
Name: http://www.ietf.org/standards/dav/patch/delete
Purpose: Removes the specified range of octets.
Schema: http://www.ietf.org/standards/dav/patch/
Parent: ResourceUpdate
Value: The Delete XML elementXML element MUST contain an
octet-
range XML elementXML element. The value of this XML elementXML
element is empty.
Discussion: The octets which are deleted are removed, which means
the resource is collapsed and the length of the resource is
decremented by the size of the octet range. It is not
appropriate to replace deleted octets with zeroed-out octets,
since zero is a valid octet value.
3.9.4.4 Replace
Name: http://www.ietf.org/standards/dav/patch/replace
Purpose: Replaces the specified range of octets with the
contents of the XML element. If the number of octets in the XML
element is different from the number of octets specified, the
update MUST be rejected.
Schema: http://www.ietf.org/standards/dav/patch/
Parent: ResourceUpdate
Value: The Replace XML element MUST contain an octet-range XML
element. The contents of the entity are the replacement octets.
3.9.4.5 Octet-Range Attribute
Name: http://www.ietf.org/standards/dav/patch/octet-
range
Purpose: Specifies a range of octets which the enclosing
property effects.
Schema: http://www.ietf.org/standards/dav/patch/
Parent: Insert, Delete, Replace
Value: number ["-" (number | "end")]
Number = 1*Digit
Description: Octet numbering begins with 0. If the octet contains
a single number then the operation is to begin at that octet and
to continue for a length specified by the operation. In the case
of a delete, this would mean to delete but a single octet. In the
case of an insert this would mean to begin the insertion at the
specified octet and to continue for the length of the included
value, extending the resource if necessary. In the case of
replace, the replace begins at the specified octet and overwrites
all that follow to the length of the included value. Octet
values MUST specify locations in the state of the resource prior
to the processing of the PATCH method.
3.9.5 The Response
200 (OK) - The request entity body was processed without error,
resulting in an update to the state of the resource.
409 (Conflict) - If the update information in the request message
body does not make sense given the current state of the resource
(e.g., an instruction to delete a non-existent line), this status
code MAY be returned.
415 (Unsupported Media Type) - The server does not support the
content type of the update instructions in the request message
body.
416 (Unprocessable Entity) - A new status code. The server
understands the content type of the request entity, but was
unable to process the contained instructions.
3.9.6 Examples
3.9.6.1 HTML file modification
The following example shows a modification of the title and
contents of the HTML resource http://www.example.org/hello.html.
Before:
<HTML>
<HEAD>
<TITLE>Hello world HTML page</TITLE>
</HEAD>
<BODY>
<P>Hello, world!</P>
</BODY>
</HTML>
PATCH Request: Response:
PATCH hello.html HTTP/1.1
Host: www.example.org
Content-Type: application/xml
Content-Length: xxx
HTTP/1.1 100 Continue
<XML>
<XML:Namespace><ref>http://www.ietf.org/standards/dav/patch/
</><AS>D</></>
<D:ResourceUpdate>
<Replace><octet-range>14</>&003CTITLE&003ENew
Title&003C/TITLE&003E</>
<Delete><octet-range>38-50</>
<Insert><octet-range>86</>&003CP&003ENew
paragraph&003C/P&003E
</>
</></>
HTTP/1.1 200 OK
After:
<HTML>
<HEAD>
<TITLE>New Title</TITLE>
</HEAD>
<BODY>
<P>Hello, world!</P>
<P>New paragraph</P>
</BODY>
</HTML>
3.10 Headers
3.10.1 Depth
The Depth header determines the depth to which a method is
propagated on a resources children.
Depth = "Depth" ":" DepthToken
DepthToken = "0" | "1" | "infinity" | token
The optional token allows for extension. A server MUST ignore a
Depth header with an unknown value.
3.10.2 Destination
The Destination header specifies a destination resource for
methods such as COPY and MOVE, which take two URIs as parameters.
Destination= "Destination" ":" URI
3.10.3 Enforce-Live-Properties
The Enforce-Live-Properties header specifies properties that MUST
be "live" after they are copied (moved) to the destination
resource of a copy (or move). If the value "*" is given for the
header, then it designates all live properties on the source
resource.
EnforceLiveProperties = "Enforce-Live-Properties" ":" ("*" |
1#( Property-Name ))
Property-Name = <"> URI <">
3.10.4 Duplicate-Properties
The Duplicate-Properties header instructs the server whether to
duplicate the source resources properties onto the destination
resource during a COPY or MOVE. A value of "false" requires that
the server MUST NOT duplicate on the destination resource any
properties that are defined on the source resource. By default,
the value of this header is "true," and a client MAY omit this
header from a request when its value is "true."
Duplicate-Properties = "Duplicate-Properties" ":" ("true" |
"false")
3.10.5 Overwrite
The Overwrite header specifies whether the server should
overwrite the state of a non-null destination resource during a
COPY or MOVE. A value of "false" states that the server MUST NOT
perform the COPY or MOVE operation if the state of the
destination resource is non-null. By default, the value of
Overwrite is "false," and a client MAY omit this header from a
request when its value is "false." While the Overwrite header
appears to duplicate the functionality of the If-Match: * header
of HTTP/1.1, If-Match applies only to the Request-URI, and not to
the Destination of a COPY or MOVE.
Overwrite = "Overwrite" ":" ("true" | "false")
3.10.6 Destroy Header
When deleting a resource the client often wishes to specify
exactly what sort of delete is being enacted. The Destroy header,
used with PEP [Connolly et al., 1997], allows the client to
specify the end result they desire. The Destroy header is
specified as follows:
DestroyHeader = "Destroy" ":" #Choices
Choices = "VersionDestroy" | "NoUndelete" | "Undelete" |
Token
The Undelete token requests that, if possible, the resource
should be left in a state such that it can be undeleted. The
server is not required to honor this request.
The NoUndelete token requests that the resource MUST NOT be left
in a state such that it can be undeleted.
The VersionDestroy token includes the functionality of the
NoUndelete token and extends it to include having the server
remove all versioning references to the resource that it has
control over.
3.10.7 Mandatory header
The Mandatory header is used to indicate a list of other header
field names which must be understood by the receiver before the
contents of the message can be stored, cached, or presented to a
user. This header is used to alert the receiver that, unlike the
default behavior, it cannot safely ignore the semantics of the
listed field-names if they are not understood.
Mandatory = "Mandatory" ":" 1#field-name
3.10.8 Collection-Member Header
The Collection-Member header specifies the URI of an external
resource to be added/deleted to/from a collection.
CollectionMember = "Collection-Member" ":" PropType SP URI
PropType = "propagation" "=" ("prop" | "noprop")
3.11 Links
3.11.1 Source Link Property Type
Name: http://www.ietf.org/standards/dav/link/source
Purpose: The destination of the source link identifies the
resource that contains the unprocessed source of the links
source.
Schema: http://www.ietf.org/standards/dav/link/
Parent: Any.
Value: An XML document with zero or more link XML elements.
Discussion: The source of the link (src) is typically the URI of
the output resource on which the link is defined, and there is
typically only one destination (dst) of the link, which is the
URI where the unprocessed source of the resource may be accessed.
When more than one link destination exists, DAV asserts no policy
on partial ordering.
4 State Tokens
4.1 Overview
4.1.1 Problem Description
There are times when a principal will want to predicate
successful execution of a method on the current state of a
resource. While HTTP/1.1 provides a mechanism for conditional
execution of methods using entity tags via the "If-Match" and
"If-
None-Match" headers, the mechanism is not sufficiently extensible
to express conditional statements involving more generic state
indicators, such as lock tokens.
The fundamental issue with entity tags is that they can only be
generated by a resource. However there are times when a client
will want to be able to share state tokens between resources,
potentially on different servers, as well as be able to generate
certain types of lock tokens without first having to communicate
with a server.
For example, a principal may wish to require that resource B have
a certain state in order for a method to successfully execute on
resource A. If the client submits an e-tag from resource B to
resource A, then A has no way of knowing that the e-tag is meant
to describe resource B.
Another example occurs when a principal wishes to predicate the
successful completion of a method on the absence of any locks on
a resource. It is not sufficient to submit an "If-None-Match: *"
as this refers to the existence of an entity, not of a lock.
This draft defines the term "state token" as an identifier for a
state of a resource. The sections below define requirements for
state tokens and provide a state token syntax, along with two
new headers which can accept the new state token syntax.
4.1.2 Solution Requirements
4.1.2.1 Syntax
Self-Describing. A state token must be self describing such that
upon inspecting a state token it is possible to determine what
sort of state token it is, what resource(s) it applies to, and
what state it represents.
This self-describing nature allows servers to accept tokens from
other servers and potentially be able to coordinate state
information cross resource and cross site through standardized
protocols. For example, the execution of a request on resource A
can be predicated on the state of resource B, where A and B are
potentially on different servers.
Client Generable. The state token syntax must allow, when
appropriate, for clients to generate a state token without having
first communicated with a server.
One drawback of entity tags is that they are set by the server,
and there is no interoperable algorithm for calculating an entity
tag. Consequently, a client cannot generate an entity tag from a
particular state of a resource. However, a state token which
encodes an MD5 state hash could be calculated by a client based
on a client-held state of a resource, and then submitted to a
server in a conditional method invocation.
Another potential use for client generable state tokens is for a
client to generate lock tokens with wild card fields, and hence
be able to express conditionals such as: "only execute this GET
if there are no write locks on this resource."
4.1.2.2 Conditonals
Universal. A solution must be applicable to all requests.
Positive and Negative. Conditional expressions must allow for the
expression of both positive and negative state requirements.
4.2 State Token Syntax
State tokens are URLs employing the following syntax:
State-Token = "StateToken:" Type ":" Resources ":" State-Info
Type = "Type" "=" Caret-encoded-URL
Resources = "Res" "=" Caret-encoded-URL
Caret-encoded-URL = "^" Resource "^"
Resource = <A URI where all "^" characters are escaped>
State-Info = *(uchar | reserved) ; uchar, reserved defined
section 3.2.1 of RFC 2068
This proposal has created a new URL scheme for state tokens
because a state token names a network resource using its normal
name, which is typically state-invariant, along with additional
information that specifies a particular state of the resource.
Encoding the state information into the native URL scheme of the
network resource was not felt to be safe, since freedom from name
space collisions could not be guaranteed. If this proposal is
accepted, the StateToken URL scheme will need to be defined and
registered with IANA.
State Token URLs begin with the URL scheme name "StateToken"
rather than the name of the particular state token type they
represent in order to make the URL self describing. Thus it is
possible to examine the URL and know, at a minimum, that it is a
state token.
Labeled name/value pairs are used within the token to allow new
fields to be added. Processors of state tokens MUST be prepared
to accept the fields in whatever order they are present and MUST
ignore any fields they do not understand.
The "Type" field specifies the type of the state information
encoded in the state token. A URL is used in order to avoid
namespace collisions.
The "Res" field identifies the resource for which the state token
specifies a particular state. Since commas and spaces are
acceptable URL characters, a caret is used to delimit a URL.
Since a caret is an acceptable URL character, any instances of it
must be escaped using the % escape convention.
The State-Info production is expanded upon in descriptions of
specific state token types, and is intended to contain the state
description information for a particular state token.
4.3 State Token Conditional Headers
4.3.1 If-State-Match
If-State-Match = "If-State-Match" ":" ("AND" | "OR") 1#("<"
State-
Token ">")
The If-State-Match header is intended to have similar
functionality to the If-Match header defined in section 14.25 of
RFC 2068.
If the AND keyword is used and all of the state tokens identify
the state of the resource, then the server MAY perform the
requested method. If the OR keyword is used and any of the state
tokens identifies the current state of the resource, then server
MAY perform the requested method. If neither of the keyword
requirements is met, the server MUST NOT perform the requested
method, and MUST return a 412 (Precondition Failed) response.
4.3.2 If-None-State-Match
If-None-State-Match = "If-None-State-Match" ":" 1#("<" State-
Token ">")
The If-None-State-Match header is intended to have similar
functionality to the If-None-Match header defined in section
14.26 of RFC 2068.
If any of the state tokens identifies the current state of the
resource, the server MUST NOT perform the requested method.
Instead, if the request method was GET, HEAD, INDEX, or GETMETA,
the server SHOULD respond with a 304 (Not Modified) response,
including the cache-related entity-header fields (particularly
ETag) of the current state of the resource. For all other
request methods, the server MUST respond with a status of 412
(Precondition Failed).
If none of the state tokens identifies the current state of the
resource, the server MAY perform the requested method.
Note that the "AND" and "OR" keywords specified with the If-
State-
Match header are intentionally not defined for If-None-State-
Match, because this functionality is not required.
4.4 State Token Header
State-Token-Header = "State-Token" ":" 1#("<" State-Token ">")
The State Token header is intended to have similar functionality
to the etag header defined in section 14.20 of RFC 2068. The
purpose of the tag is to return state tokens defined on a
resource in a response. The contents of the state-token are not
guaranteed to be exhaustive and are generally used to return a
new state token that has been defined as the result of a method.
For example, if a LOCK method were successfully executed on a
resource the response would include a state token header with the
lock state token included.
4.5 E-Tags
E-tags have already been deployed using the If-Match and If-None-
Match headers. Introducing two mechanisms to express e-tags
would only confuse matters, therefore e-tags should continue to
be expressed using quoted strings and the If-Match and If-None-
Match headers.
5 Locking
5.1 Problem Description - Overview
Locking is used to arbitrate access to a resource amongst
principals that have equal access rights to that resource.
This draft allows locks to vary over two parameters, the number
of principals involved and the type of access to be granted. This
draft will only provide for the definition of locking for one
access type, write. However, the syntax is extensible enough to
allow for the specification of other access types. It is a goal
of this proposal that it use the same access verbs as will be
defined in the access control draft.
5.1.1 Exclusive Vs. Shared Locks
The most basic form of LOCK is an exclusive lock. This is a lock
where the access right in question is only granted to a single
principal. The need for this arbitration results from a desire to
avoid having to constantly merge results. In fact, many users so
dislike having to merge that they would rather serialize their
access to a resource rather than have to constantly perform
merges.
However, there are times when the goal of a lock is not to
exclude others from exercising an access right but rather to
provide a mechanism for principals to indicate that they intend
to exercise their access right. Shared locks are provided for
this case. A shared lock allows multiple principals to receive a
lock, hence any principal with appropriate access can get the
lock.
With shared locks there are two trust sets that affect a
resource. The first trust set is created by access permissions.
Principals who are trusted, for example, may have permission to
write the resource, those who are not, don't. Among those who
have access permission to write the resource, the set of
principals who have taken out a shared lock also must trust each
other, creating a (probably) smaller trust set within the access
permission write set.
Starting with every possible principal on the Internet, in most
situations the vast majority of these principals will not have
write access to a given resource. Of the small number who do
have write access, some principals may decide to guarantee their
edits are free from overwrite conflicts by using exclusive write
locks in conjunction with a precondition header (If-State-Match)
that checks for existence of the lock prior to writing the
resource. Others may decide they trust their collaborators (the
potential set of collaborators being the set of principals who
have write permission) and use a shared lock, which informs their
collaborators that a principal is potentially working on the
resource.
The WebDAV extensions to HTTP do not need to provide all of the
communications paths necessary for principals to coordinate their
activities. When using shared locks, principals may use any out
of band communication channel to coordinate their work (e.g.,
face-to-face interaction, written notes, post-it notes on the
screen, telephone conversation, email). The intent of a shared
lock is to let collaborators know who else is potentially working
on a resource.
Why not use exclusive write locks all the time? Experience from
initial Web distributed authoring systems has indicated that
exclusive write locks are often too rigid. An exclusive write
lock is used to enforce a particular editing process: take out
exclusive write lock, read the resource, perform edits, write the
resource, release the lock. What happens if the lock isn't
released? While the time-out mechanism provides one solution, if
you need to force the release of a lock immediately, it doesn't
help much. Granted, an administrator can release the lock for
you, but this could become a significant burden for large sites.
Further, what if the administrator can't be reached immediately?
Despite their potential problems, exclusive write locks are
extremely useful, since often a guarantee of freedom from
overwrite conflicts is exactly what is needed. The solution:
provide exclusive write locks, but also provide a less strict
mechanism in the form of shared locks which can be used by a set
of people who trust each other and who have access to a
communications channel external to HTTP which can be used to
negotiate writing to the resource.
5.1.2 Required Support
A DAV compliant server is not required to support locking in any
form. If the server does support locking it may choose to support
any combination of exclusive and shared locks for any access
types.
The reason for this flexibility is that server implementers have
said that they are willing to accept minimum requirements on all
services but locking. Locking policy strikes to the very heart of
their resource management and versioning systems and they require
control over what sort of locking will be made available. For
example, some systems only support shared write locks while
others only provide support for exclusive write locks. As each
system is sufficiently different to merit exclusion of certain
locking features, the authors are proposing that locking be
allowed as the sole axis of negotiation within DAV.
5.2 LOCK Method
5.2.1 Operation
A lock method invocation creates the lock specified by the Lock-
Info header on the request-URI. Lock method requests SHOULD NOT
have a request body. A user-agent SHOULD submit an Owner header
field with a lock request.
A successful response to a lock invocation MUST include a Lock-
Token header. If the server supports a time based lock removal
mechanism on the resource, a successful lock invocation SHOULD
return a Time-Out header.
5.2.2 Effect of Locks on Properties and Containers
By default a lock affects the entire state of the resource,
including its associated properties. As such it is illegal to
specify a lock on a property. For containers, a lock also affects
the ability to add or remove members. The nature of the effect
depends upon the type of access control involved. The Depth
header expresses the general semantics of a LOCK method request
when invoked on a collection (note that specific lock types may
restrict the effect of a lock, for example limiting the allowable
values of the Depth header):
· A Depth header (defined in the namespace draft) may be used
on a LOCK method when the LOCK method is applied to a
collection
resource. The legal values for Depth on a LOCK are 0, 1, and
Infinity. A Depth of 0 instructs the resource to just lock the
container. As previously mentioned, depending on the type of
lock, the lock affects the ability to add or remove members of
the container.
· A Depth of 1 means that the container is locked and a LOCK
is executed on the containers propagate members with a Depth
of
0 and If-Range, If-Modified-Since, If-Unmodified-Since, If-
Match
and If-None-Match headers are dropped. However, the effects of
the LOCK MUST be atomic in that either the container and all of
its members are locked or no lock is granted. The result of a
Depth 1 lock is a single lock token which represents the lock
on
the container and all of its members. This lock token may be
used
in an If-State-Match or If-Not-State-Match header against any
of
the resources covered by the lock. Since the lock token
represents a lock on all the resources, an UNLOCK using that
token will remove the lock from all included resources, not
just
the resource the UNLOCK was executed on.
· A Depth of infinity means that the LOCK is recursively
executed, with a Depth of infinity, on the collection and all of
its propagate members and all of their propagate members. As with
a Depth of 1, the LOCK must be granted in total or not at all.
Otherwise the lock operates in the same manner as a Depth of 1
lock.
The default behavior when locking a container is to act as if a
"Depth: 0" header had been placed on the method.
5.2.3 Locking Replicated Resources
Some servers automatically replicate resources across multiple
URLs. In such a circumstance the server MAY only accept a lock on
one of the URLs if the server can guarantee that the lock will be
honored across all the URLs.
5.2.4 Interaction with other Methods
Only two methods, MOVE and DELETE, have side effects which
involve locks. When a resource is moved, its lock SHOULD be moved
with it. However this may not always be possible and there is
currently no proposal to create a header which would specify that
the lock request should fail if the resources locks can not be
maintained. A COPY MUST NOT copy any locks on the source resource
over to the destination resource. Deleting a resource MUST remove
all locks on the resource.
5.2.5 Lock Compatibility Table
The table below describes the behavior that occurs when a lock
request is made on a resource.
Current lock state/ Shared Lock Exclusive Lock
Lock request
None True True
Shared Lock True False
Exclusive Lock False False*
Legend: True = lock MAY be granted. False = lock MUST NOT be
granted. *=if the principal requesting the lock is the owner of
the lock, the lock MAY be regranted.
The current lock state of a resource is given in the leftmost
column, and lock requests are listed in the first row. The
intersection of a row and column gives the result of a lock
request. For example, if a shared lock is held on a resource,
and an exclusive lock is requested, the table entry is "false",
indicating the lock must not be granted.
If an exclusive lock is re-requested by the principal who owns
the lock, the lock MAY be regranted. If the lock is regranted,
the same lock token that was previously issued MUST be returned.
5.2.6 Status Codes
412 "Precondition Failed" - The included state-token was not
enforceable on this resource.
416 "Locked" - The resource is locked so the method has been
rejected.
5.2.7 Example
LOCK /workspace/webdav/proposal.doc HTTP/1.1
Host: webdav.sb.aol.com
Lock-Info: LockType=Write LockScope=Exclusive
Owner: <http://www.ics.uci.edu/~ejw/contact.html>
HTTP/1.1 200 OK
State-Token: StateToken:Type=^DAV:/LOCK/DAVLOCK^:Res=^http://www.
ics.uci.edu/workspace/webdav/proposal.doc^:LockType=Write:LockSco
pe=Exclusive:ServerID=12382349AdfFFF
Time-Out: ClockType=Activity TimeType=second;604800
This example shows the successful creation of an exclusive write
lock on resource
http://webdav.sb.aol.com/workspace/webdav/proposal.doc. The
resource http://www.ics.uci.edu/~ejw/contact.html contains
contact information for the owner of the lock. The server has an
activity-based timeout policy in place on this resource, which
causes the lock to automatically be removed after 1 week (604800
seconds). The response has a Lock-Token header that gives the
state token URL for the lock token generated by this lock
request.
5.2.8 Lock-Info Request Header
The Lock-Info header specifies the scope and type of a lock for a
LOCK method request. The syntax specification below is
extensible, allowing new type and scope identifiers to be added.
LockInfo = "Lock-Info" ":" DAVLockType SP DAVLockScope CRLF
DAVLockType = "LockType" "=" DAVLockTypeValue
DAVLockTypeValue = ("Write" | *(uchar | reserved))
DAVLockScope = "LockScope" "=" DAVLockScopeValue
DAVLockScopeValue = ("Exclusive" |"Shared" | *(uchar | reserved))
5.2.9 Owner Request Header
5.2.9.1 Problem Description
When discovering the list of owners of locks on a resource, a
principal may want to be able to contact the owner directly. For
this to be possible the lock discovery mechanism must provide
enough information for the lock owner to be contacted.
5.2.9.2 Solution Requirements
Not all systems have authentication procedures that provide
sufficient information to identify a particular user in a way
that is meaningful to a human. In addition, many systems that do
have sufficient information, such as a name and e-mail address,
do not have the ability to associate this information with the
lock discovery mechanism. Therefore a means is needed to allow
principals to provide authentication in a manner which will be
meaningful to a human.
The From header (defined in RFC 2068), which contains only an
email mailbox, is not sufficient for the purposes of quick
identification. When desperately looking for someone to remove a
lock, e-mail is often not sufficient. A telephone number (cell
number, pager number, etc.) would be better. Furthermore, the
email address in the From field may or may not support including
the owners name and that name is often set to an alias anyway.
Therefore a header more flexible than From is required.
5.2.9.3 Syntax
Owner = "Owner" ":" (("<" URI ">") | quoted-string)
The URI SHOULD provide a means for either directly contacting the
principal (such as a telephone number or e-mail URI), or for
discovering the principal (such as the URL of a homepage). The
quoted string SHOULD provide a means for directly contacting the
principal, such as a name and telephone number.
5.2.10 Time-Out Header
5.2.10.1 Problem Description
In a perfect world principals take out locks, use the resource as
needed, and then remove the lock when it is no longer needed.
However, this scenario is frequently not completed, leaving
active but unused locks. Reasons for this include client programs
crashing and loosing information about locks, users leaving their
systems for the day and forgetting to remove their locks, etc. As
a result of this behavior, servers need to establish a policy by
which they can remove a lock without input from the lock owner.
Once such a policy is instituted, the server also needs a
mechanism to inform the principal of the policy.
5.2.10.2 Solution Requirements
There are two basic lock removal policies, administrator and time
based remove. In the first case a principal other than the lock
owner has sufficient access rights to order the lock removed,
even though they did not take it out. User-agents MUST assume
that such a mechanism is available and thus locks may arbitrarily
disappear at any time. If their actions require confirmation of
the existence of a lock then the If-State headers are available.
The second solution, is the time based removal policy. Activity
based systems set a timer as soon as the lock is taken out. Every
time a method is executed on the resource, the timer is reset. If
the timer runs out, the lock is removed.
Finally, some systems only allow locks to exist for the duration
of a session, where a session is defined as the time when the
HTTP connection that was used to take out the lock remains
connected. This mechanism is used to allow programs which are
likely to be improperly exited, such as JAVA programs running in
a browser, to take out locks without leaving a lot of ownerless
locks around when they are improperly exited.
5.2.10.3 Syntax
TimeOut = "Time-Out" ":" ((TimeOutType SP Session) | TimeOutVal |
Session) CRLF
TimeOutType = ClockType SP TimeType
ClockType = "ClockType" "=" ClockTypeValue
ClockTypeValue = "Activity"
TimeType = "TimeType" "=" TimeTypeValue
TimeTypeValue = "Second" ";" DAVTimeOutVal
DAVTimeOutVal = 1*digit
Session = "Session" "=" ("Yes" | "No")
The "Second" TimeType specifies the number of seconds that may
elapse before the lock is automatically removed. A server MUST
not generate a time out value for "second" greater than 2^32-1.
If no time based system is in use then a Time-Out header MUST NOT
be returned. The Time-Out header MUST only be returned in a
response to a LOCK request.When session is set to yes then
whatever clocktype and timetype is being used, their effects are
scoped within that particular session. So an absolute lock with a
ten day expiration period will only remain active so long as the
session remains active. A DAVTimeOutVal value must be greater
than zero.
Clients MAY include TimeOut headers in their LOCK requests.
However the server is not required to honor or even consider the
request. The primary purpose in allowing clients to submit a
TimeOut header is to inform the server if the client is
requesting a session based lock. If a timeout is associated with
the lock, the server MUST return a TimeOut header with a valid
value.
5.2.11 State-Token Header
5.2.11.1 Problem Definition
Program A, used by User A, takes out a write lock on a resource.
Program B, also run by User A, then proceeds to perform a PUT to
the locked resource. The PUT will succeed because locks are
associated with a principal, not a program, and thus program B,
because it is acting with principal As credential, will be
allowed to perform the PUT. In reality program B had no knowledge
of the lock and had it had such knowledge, would not have
overwritten the resource. Hence, a mechanism is needed to prevent
different programs from accidentally ignoring locks taken out by
other programs with the same authorization.
5.2.11.2 Solution Requirement
The solution must not require principals to perform discovery in
order to prevent accidental overwrites as this could cause race
conditions.
The solution must not require that clients guess what sorts of
locks might be used and use if-state-match headers with wildcards
to prevent collisions. The problem with trying to "guess" which
locks are being used is that new lock types might be introduced,
and the program would not know to "guess them". So, for example,
a client might put in an if-state-match header with a wildcard
specifying that if any write lock is outstanding then the
operation should fail. However a new read/write lock could be
introduced which the client would not know to put in the header.
5.2.11.3 State-Token Header
The State-Token header is returned in a successful response to
the LOCK method or is used as a request header with the UNLOCK
method.
The State-Token header containing a lock token owned by the
request principal is used by the principal on arbitrary method to
indicate that the principal is aware of the specified lock. If
the State-Token header with the appropriate lock token is not
included the request MUST be rejected, even though the requesting
principal has authorization to make modifications specified by
the lock type. This injunction does not apply to methods that are
not affected by the principals lock.
For example, Program A, used by user A, takes out a write lock on
a resource. Program A then makes a number of PUT requests on the
locked resource, all the requests contain a State-Token header
which includes the write lock state token. Program B, also run by
User A, then proceeds to perform a PUT to the locked resource.
However program B was not aware of the existence of the lock and
so does not include the appropriate state-token header. The
method is rejected even though principal A is authorized to
perform the PUT. Program B can, if it so chooses, now perform
lock discovery and obtain the lock token. Note that program A and
B can perform GETs without using the state-token header because
the ability to perform a GET is not affected by a write lock.
Note that having a lock state token provides no special access
rights. Anyone can find out anyone elses lock state token by
performing lock discovery. Locks are to be enforced based upon
whatever authentication mechanism is used by the server, not
based on the secrecy of the token values.
5.3 Write Lock
A write lock prevents a principal without the lock from
successfully executing a PUT, POST, DELETE, MKCOL, PROPPATCH,
PATCH, ADDREF or DELREF on the locked resource. All other
methods, GET in particular, function independent of the lock.
While those without a write lock may not alter a property on a
resource it is still possible for the values of live properties
to change, even while locked, due to the requirements of their
schemas. Only dead properties and live properties defined to
respect locks are guaranteed to not change while locked.
It is possible to assert a write lock on a null resource in order
to lock the name. Please note, however, that locking a null
resource effectively makes the resource non-null as the resource
now has lock related properties defined on it.
Write locking a container also prevents adding or removing
members of the container. This means that attempts to PUT/POST a
resource into the immediate name space of the write locked
container MUST fail if the principal requesting the action does
not have the write lock on the container. In order to keep the
behavior of locking containers consistent all locks on containers
MUST contain a Depth header equal to infinity, any other value is
illegal.
5.4 Lock Tokens
5.4.1 Problem Description
It is possible that once a lock has been granted it may be
removed without the lock owners knowledge. This can cause
serialization problems if the lock owner executes methods
thinking their lock is still in effect. Thus a mechanism is
needed for a principal to predicate the successful execution of a
message upon the continuing existence of a lock.
5.4.2 Proposed Solution
The proposed solution is to provide a lock token in the response
of a lock request. The lock token is a type of state token and
describes a particular lock. The same lock token must never be
repeated on a particular resource. This prevents problems with
long held outstanding lock tokens being confused with newer
tokens. This uniqueness requirement is the same as for e-tags.
This requirement also allows for tokens to be submitted across
resources and servers without fear of confusion.
5.4.3 Lock Token Definition
The lock token is returned in the State-Token header in the
response to a LOCK method. The lock token can also be discovered
through lock discovery on a resource.
Lock-Token-URL = "StateToken:" Type ":" Resources ":" State-Info
Type = "Type" "=" "^DAV:/LOCK/DAVLOCK^"
Resources = "Res" "=" 1*("^" Caret-Encoded-URI "^")
Caret-Encoded-URI = <This is a URI which has all "^"s % encoded.>
State-Info = DAVLockScope ":" DAVLockType ":" ServerID ;
DAVLockScope, DAVLockType defined in Lock-Info header
ServerID = "ServerID" "=" *(uchar | reserved)
The ServerID is a field for use by the server. Its most basic
purpose is to put in a unique identifier to guarantee that a
server will never confuse an old lock token with a newer one.
However the server is free to use the field to record whatever
information it deems fit. The field is opaque to clients.
5.5 UNLOCK Method
5.5.1 Problem Definition
The UNLOCK method removes the lock identified by the lock token
in the State-Token header from the Request-URI.
5.5.2 Example
UNLOCK /workspace/webdav/proposal.doc HTTP/1.1
Host: webdav.sb.aol.com
State-Token: StateToken:Type=^DAV:/LOCK/DAVLOCK^:Res=^http://www.
ics.uci.edu/workspace/webdav/proposal.doc^:LockType=Write:LockSco
pe=Exclusive:ServerID=12382349AdfFFF
HTTP/1.1 200 OK
In this example, the lock from example of Section 2.9 is removed
from the resource at
http://webdav.sb.aol.com/workspace/webdav/proposal.doc
5.6 Discovery Mechanisms
5.6.1 Lock Type Discovery
5.6.1.1 Problem Definition
Since server lock support is optional, a client trying to lock a
resource on a server can either try the lock and hope for the
best or can perform some form of discovery to determine what lock
types the server actually supports, then formulate a supported
request. This is known as lock type discovery. Lock type
discovery is not the same as discovering what access control
types are supported, as there may be access control types without
corresponding lock types.
5.6.1.2 SupportedLock Property
Name: http://www.ietf.org/standards/dav/lock/supportedlock
Purpose: To provide a listing of the lock types supported by the
resource.
Schema: http://www.ietf.org/standards/dav/
Values: An XML document containing zero or more LockEntry XML
elements.
Description: The SupportedLock property of a resource returns a
listing of the combinations of scope and access types which may
be specified in a lock request on the resource. Note that the
actual contents are themselves controlled by access controls so a
server is not required to provide information the client is not
authorized to see. If SupportedLock is available on "*" then it
MUST define the set of locks allowed on all resources on that
server.
5.6.1.3 LOCKENTRY XML Element
Name: http://www.ietf.org/standards/dav/lockentry
Purpose: Defines a DAVLockType/LockScope pair which may be
legally used with a LOCK on the specified resource.
Schema: HYPERLINK http://www.ietf.org/standards/dav/
Parent: A SupportedLock entry
Values: LockType LockScope
5.6.1.4 LOCKTYPE XML Element
Name: http://www.ietf.org/standards/dav/locktype
Purpose: Lists a DAVLockType
Schema: http://www.ietf.org/standards/dav/
Parent: LOCKENTRY
Values: DAVLockTypeValue
5.6.1.5 LOCKSCOPE XML Element
Name: http://www.ietf.org/standards/dav/lockscope
Purpose: Lists a DAVLockScope
Schema: http://www.ietf.org/standards/dav/
Parent: LOCKENTRY
Values: DAVLockScopeValue
5.6.2 Active Lock Discovery
5.6.2.1 Problem Definition
If another principal locks a resource that a principal wishes to
access, it is useful for the second principal to be able to find
out who the first principal is.
5.6.2.2 Solution Requirements
The lock discovery mechanism should provide a list of who has the
resource locked, what locks they have, and what their lock tokens
are. The lock tokens are useful in shared lock situations where
two principals in particular may want to guarantee that they do
not overwrite each other. The lock tokens are also useful for
administrative purposes so that an administrator can remove a
lock by referring to its token.
5.6.2.3 LOCKDISCOVERY Property
Name: http://www.ietf.org/standards/dav/lockdiscovery
Purpose: To discover what locks are active on a resource
Schema: http://www.ietf.org/standards/dav/
Values= An XML document containing zero or more ActiveLock XML
elements.
Description: The LOCKDISCOVERY property returns a listing of who
has a lock, what type of lock they have, the time out type and
the time remaining on the time out, and the associated lock
token. The server is free to withhold any or all of this
information if the requesting principal does not have sufficient
access rights to see the requested data.
5.6.2.4 ACTIVELOCK XML Element
Name: http://www.ietf.org/standards/dav/activelock
Purpose: A multivalued XML element that describes a particular
active lock on a resource
Schema: http://www.ietf.org/standards/dav/
Parent: A LOCKDISCOVERY entry
Values= LOCKTYPE LOCKSCOPE OWNER TIMEOUT LOCKTOKEN
5.6.2.5 OWNER XML Element
Name: http://www.ietf.org/standards/dav/lock/owner
Purpose: Returns owner information
Schema: http://www.ietf.org/standards/dav/
Parent: ACTIVELOCK
Values= XML:REF | {any valid XML string}
5.6.2.6 TIMEOUT XML Element
Name: http://www.ietf.org/standards/dav/timeout
Purpose: Returns information about the timeout associated with
the lock
Schema: http://www.ietf.org/standards/dav/
Parent: ACTIVELOCK
Values= CLOCKTYPE TIMETYPE TIMEOUTVAL
5.6.2.7 CLOCKTYPE XML Element
Name: http://www.ietf.org/standards/dav/clocktype
Purpose: Returns the clock type used with this lock
Schema: http://www.ietf.org/standards/dav/
Parent: TIMEOUT
Values= ClockTypeValue
5.6.2.8 TIMETYPE XML Element
Name: http://www.ietf.org/standards/dav/clocktype
Purpose: Returns the time type used with this lock
Schema: http://www.ietf.org/standards/dav/
Parent: TIMEOUT
Values= TimeTypeValue
5.6.2.9 TIMEOUTVAL XML Element
Name: http://www.ietf.org/standards/dav/timeoutval
Purpose: Returns the amount of time left on the lock
Schema: http://www.ietf.org/standards/dav/
Parent: TIMEOUT
Values= DAVTimeOutVal
5.6.2.10 LOCKTOKEN XML Element
Name: http://www.ietf.org/standards/dav/statetoken
Purpose: Returns the lock token
Schema: http://www.ietf.org/standards/dav/
Parent: ACTIVELOCK
Values= XML:REF
Description: The REF contains a Lock-Token-URL.
6 Version Control
[TBD]
7 Internationalization Support
[TBD]
8 Security Considerations
[TBD]
9 Acknowledgements
Terry Allen, Harald Alvestrand, Alan Babich, Dylan Barrell,
Bernard Chester, Dan Connolly, Jim Cunningham, Ron Daniel, Jr.,
Keith Dawson, Mark Day, Martin Duerst, David Durand, Lee Farrell,
Chuck Fay, Roy Fielding, Mark Fisher, Alan Freier, George
Florentine, Jim Gettys, Phill Hallam-Baker, Dennis Hamilton,
Steve Henning, Alex Hopmann, Andre van der Hoek, Ben Laurie, Paul
Leach, Ora Lassila, Karen MacArthur, Steven Martin, Larry
Masinter, Michael Mealling, Keith Moore, Henrik Nielsen, Kenji
Ota, Bob Parker, Glenn Peterson, Jon Radoff, Saveen Reddy, Henry
Sanders, Christopher Seiwald, Judith Slein, Mike Spreitzer, Einar
Stefferud, Ralph Swick, Kenji Takahashi, Robert Thau, Sankar
Virdhagriswaran, Fabio Vitali, Gregory Woodhouse, Lauren Wood
10 References
[Berners-Lee, 1997] T. Berners-Lee, "Metadata Architecture."
Unpublished white paper, January 1997.
http://www.w3.org/pub/WWW/DesignIssues/Metadata.html.
[Bray, Sperberg-McQueen, 1997] T. Bray, C. M. Sperberg-McQueen,
"Extensible Markup Language (XML): Part I. Syntax", WD-xml-
lang.html, http://www.w3.org/pub/WWW/TR/WD-xml-lang.html.
[Connolly et al, 1997] D. Connolly, R. Khare, H.F. Nielsen, "PEP
- an Extension Mechanism for HTTP", Internet draft, work-in-
progress. draft-ietf-http-pep-04.txt,
ftp://ds.internic.net/internet-drafts/draft-ietf-http-pep-04.txt.
[Fielding et al., 1997] R. Fielding, J. Gettys, J. Mogul, H.
Frystyk, T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1." RFC 2068. U.C. Irvine, DEC, MIT/LCS. January, 1997.
[Lasher, Cohen, 1995] R. Lasher, D. Cohen, "A Format for
Bibliographic Records," RFC 1807. Stanford, Myricom. June, 1995.
[Maloney, 1996] M. Maloney, "Hypertext Links in HTML." Internet
draft (expired), work-in-progress, January, 1996.
[MARC, 1994] Network Development and MARC Standards, Office, ed.
1994. "USMARC Format for Bibliographic Data", 1994. Washington,
DC: Cataloging Distribution Service, Library of Congress.
[Miller et al., 1996] J. Miller, T. Krauskopf, P. Resnick, W.
Treese, "PICS Label Distribution Label Syntax and Communication
Protocols" Version 1.1, W3C Recommendation REC-PICS-labels-
961031. http://www.w3.org/pub/WWW/TR/REC-PICS-labels-961031.html.
[Slein et al., 1997] J. A. Slein, F. Vitali, E. J. Whitehead,
Jr., D. Durand, "Requirements for Distributed Authoring and
Versioning on the World Wide Web." Internet-draft, work-in-
progress, draft-ietf-webdav-requirements-02.txt,
ftp://ds.internic.net/internet-drafts/draft-ietf-webdav-
requirements-02.txt.
[WebDAV, 1997] WEBDAV Design Team. "A Proposal for Web Metadata
Operations." Unpublished manuscript.
http://www.ics.uci.edu/~ejw/authoring/proposals/metadata.html
[Weibel et al., 1995] S. Weibel, J. Godby, E. Miller, R. Daniel,
"OCLC/NCSA Metadata Workshop Report."
http://purl.oclc.org/metadata/dublin_core_report.
[Yergeau, 1997] F. Yergeau, "UTF-8, a transformation format of
Unicode and ISO 10646", Internet Draft, work-in-progress, draft-
yergeau-utf8-rev-00.txt, http://www.internic.net/internet-
drafts/draft-yergeau-utf8-rev-00.txt.
11 Authors' Addresses
Y. Y. Goland
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
Email yarong@microsoft.com
E. J. Whitehead, Jr.
Dept. Of Information and Computer Science
University of California, Irvine
Irvine, CA 92697-3425
Email: ejw@ics.uci.edu
A. Faizi
Netscape
685 East Middlefield Road
Mountain View, CA 94043
Email: asad@netscape.com
S. R Carter
Novell
1555 N. Technology Way
M/S ORM F111
Orem, UT 84097-2399
Email srcarter@novell.com
D. Jensen
Novell
1555 N. Technology Way
M/S ORM F111
Orem, UT 84097-2399
Email dcjensen@novell.com
Datatracker
Report a datatracker bug
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