INTERNET-DRAFT Geoffrey Clemm, Rational Software
draft-ietf-deltav-versioning-04 Chris Kaler, Microsoft
Expires November 10, 2000 May 10, 2000
Versioning Extensions to WebDAV
Status of this Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups. Note that other groups
may also distribute working documents as Internet-Drafts.
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or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
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The list of Internet-Draft Shadow Directories can be accessed at
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Abstract
This document specifies a set of methods, headers, and resource-types
that define the WebDAV Versioning extensions to the HTTP/1.1 protocol.
WebDAV Versioning will minimize the complexity of clients so as to
facilitate widespread deployment of applications capable of utilizing
the WebDAV Versioning services. WebDAV Versioning includes:
- Basic versioning with automatic versioning for versioning-unaware
clients,
- Activity and configuration management,
- URL namespace versioning.
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Table of Contents
1 INTRODUCTION...........................................5
1.1 Relationship to DAV...................................5
1.2 Terms.................................................5
1.3 Notational Conventions................................7
2 WEBDAV VERSIONING SEMANTICS............................7
2.1 Creating and Modifying Versioned Resources............7
2.2 Naming Working Resources: Workspaces..................9
2.3 Naming Revisions: Revision Ids and Revision Labels....9
2.4 Accessing Versioned Resources: Workspace and Revision-Selector
Headers...................................................9
3 VERSIONING PROPERTIES BY RESOURCE TYPE.................9
3.1 Common Property Values...............................10
3.1.1 boolean Syntax...................................10
3.1.2 segment Syntax...................................10
3.1.3 date-time Syntax.................................10
3.1.4 href XML Element.................................10
3.1.5 stable href......................................10
3.2 Resource Properties..................................10
3.2.1 DAV:author.......................................10
3.2.2 DAV:comment......................................10
3.3 Versioned Resource Properties........................11
3.3.1 DAV:revision-set (protected).....................11
3.3.2 DAV:initial-revision (protected).................11
3.3.3 DAV:default-revision.............................11
3.3.4 DAV:auto-version.................................11
3.4 Revision Properties..................................11
3.4.1 DAV:revision-id (protected)......................11
3.4.2 DAV:revision (protected).........................12
3.4.3 DAV:predecessor-set (protected)..................12
3.4.4 DAV:successor-set (protected)....................12
3.4.5 DAV:label-set (protected)........................12
3.4.6 DAV:checkin-date (protected).....................13
3.4.7 DAV:workspace-set (protected)....................13
3.4.8 DAV:single-checkout..............................13
3.4.9 DAV:versioned-resource (protected)...............13
3.5 Working Resource Properties..........................13
3.5.1 DAV:workspace (protected)........................13
3.5.2 DAV:predecessor-set (protected)..................13
3.5.3 DAV:checkin-policy...............................14
4 VERSIONING AND EXISTING METHODS.......................14
4.1 Automatic Versioning for Versioning Unaware Clients..14
4.2 New Status Codes for Existing Methods................15
5 NEW WEBDAV METHODS....................................15
5.1 MKRESOURCE...........................................15
5.1.1 Example - MKRESOURCE.............................16
5.2 REPORT...............................................16
5.2.1 DAV:report-request...............................17
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5.2.2 DAV:report-response..............................17
5.3 Available REPORT.....................................17
5.3.1 DAV:available-report-request.....................17
5.3.2 DAV:available-report-response....................17
5.3.3 Example - Available REPORT.......................18
5.4 Property REPORT......................................18
5.4.1 DAV:property-report-request......................18
5.4.2 DAV:property-report-response.....................19
5.4.3 Example - Property REPORT........................19
6 VERSIONING METHODS....................................19
6.1 VERSION..............................................19
6.1.1 Example - VERSION................................20
6.2 CHECKOUT.............................................20
6.2.1 Example - CHECKOUT...............................21
6.3 UNCHECKOUT...........................................22
6.3.1 Example - UNCHECKOUT.............................22
6.4 CHECKIN..............................................22
6.4.1 Example - CHECKIN................................23
6.5 LABEL................................................24
6.5.1 Example - LABEL..................................24
7 VERSIONING HEADERS....................................25
7.1 Workspace............................................25
7.2 Revision-Selector....................................25
8 ADVANCED VERSIONING...................................26
8.1 Advanced Versioning Terms............................26
9 ADVANCED VERSIONING SEMANTICS.........................29
9.1 Revision Selection and Workspaces....................29
9.2 Parallel Development, Activities, and Merging........29
9.3 Configurations.......................................30
9.4 Versioned Collections................................30
9.5 Repositories.........................................31
10 ADVANCED VERSIONING PROPERTIES BY RESOURCE TYPE......31
10.1 Collection Properties..............................31
10.1.1 DAV:default-workspace............................31
10.2 Versioned Resource Properties......................31
10.2.1 DAV:baselines (protected)........................32
10.2.2 DAV:baselines-root (protected)...................35
10.2.3 DAV:repository (protected).......................32
10.3 Revision Properties................................32
10.3.1 DAV:activity.....................................32
10.4 Working Resource Properties........................32
10.4.1 DAV:activity.....................................32
10.5 Workspace Properties...............................32
10.5.1 DAV:working-resource-set (protected).............32
10.5.2 DAV:revision-selection-rule......................33
10.5.3 DAV:no-checkout..................................34
10.5.4 DAV:current-label................................34
10.5.5 DAV:current-activity.............................34
10.6 Activity Properties................................35
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10.6.1 DAV:revision-set (protected).....................35
10.6.2 DAV:needed-activity-set..........................35
10.6.3 DAV:workspace-set (protected)....................35
10.7 Configuration Properties...........................35
10.8 Baseline Properties................................35
10.9 Repository Properties..............................36
10.9.1 DAV:versioned-resource-collection (protected)....36
10.9.2 DAV:repository-root (protected)..................36
10.9.3 DAV:activity-collection (protected)..............36
10.9.4 DAV:configuration-collection (protected).........36
11 ADVANCED VERSIONING AND EXISTING METHODS.............36
11.1 LOCK...............................................37
11.2 CHECKOUT...........................................37
11.3 CHECKIN............................................37
12 ADVANCED VERSIONING REPORTS..........................38
12.1 Conflict REPORT....................................38
12.1.1 DAV:conflict-report-request......................38
12.1.2 DAV:conflict-report-response.....................38
12.1.3 Example - Conflict REPORT........................38
12.2 Compare REPORT.....................................39
12.2.1 DAV:compare-report-request.......................39
12.2.2 DAV:compare-report-response......................40
12.2.3 Example - Compare REPORT.........................40
13 ADVANCED VERSIONING METHODS..........................41
13.1 MERGE..............................................41
13.1.1 Example - MERGE..................................42
13.2 BASELINE...........................................42
13.2.1 Example - BASELINE...............................44
14 ADVANCED VERSIONING HEADERS..........................44
14.1 Workspace..........................................44
15 INTERNATIONALIZATION CONSIDERATIONS..................44
16 SECURITY CONSIDERATIONS..............................44
17 SCALABILITY..........................................44
18 AUTHENTICATION.......................................44
19 IANA CONSIDERATIONS..................................44
20 INTELLECTUAL PROPERTY................................45
21 ACKNOWLEDGEMENTS.....................................45
22 INDEX................................................45
23 REFERENCES...........................................45
24 AUTHORS' ADDRESSES...................................46
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25 OPEN ISSUES..........................................46
1 INTRODUCTION
This document defines WebDAV Versioning extensions, an application
of HTTP/1.1 for handling resource versioning in a WebDAV
environment. [Goals] describes the motivation and requirements for
these extensions. WebDAV Versioning defines two levels of
versioning functionality: basic versioning and advanced versioning.
Basic versioning provides versioning of largely independent
resources. It allows authors to concurrently create, label, and
access distinct revisions of a resource, and provides automatic
versioning for versioning-unaware clients. All basic versioning
functionality MUST be provided by a versioned resource that
supports versioning.
Advanced versioning provides more sophisticated capabilities such
as logical change tracking, configuration management, and
versioning the URL namespace. A particular versioned resource may
support only a subset of the advanced versioning capabilities. The
advanced versioning capabilities provided by a particular versioned
resource may be discovered with an OPTIONS request.
This document will first define the terminology, semantics,
properties, methods, and headers for basic versioning, and then
define the additional terminology, semantics, properties, and
methods for advanced versioning.
1.1 Relationship to DAV
To maximize interoperability and the use of existing protocol
functionality, versioning support is designed as extensions to the
WebDAV [RFC2518] and Binding protocols [Binding]. In particular,
WebDAV Versioning relies on the resource and property model defined
by [RFC2518] and the binding model defined by [Binding].
1.2 Terms
This draft uses the terms defined in [RFC2068] and [RFC2518]. In
addition, the following terms are defined:
Versionable Resource
A "versionable resource" is a resource that can be placed under
version control with a VERSION request.
Versioned Resource
A "versioned resource" is a resource that is under version control.
A versioned resource tracks the history of its significant states.
To update a resource under version control, it must be checked out
and then subsequently checked in.
Working Resource
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A "working resource" is a writeable resource created by applying a
CHECKOUT request to a revision of a versioned resource.
Workspace
A "workspace" is a string chosen by the server to identify a
particular working resource of a versioned resource.
Revision
A "revision" of a versioned resource is a write-protected resource
created by applying a CHECKIN request to a working resource.
Revision Id
A "revision id" is a string chosen by the server to identify a
particular revision of a versioned resource.
Revision Label
A "revision label" is a string chosen by a client to identify a
particular revision of a versioned resource..
Initial Revision
An "initial revision" is the first revision of a versioned
resource.
Predecessor, Successor
A "predecessor" of a revision is a previous revision that was
checked out or merged to create the revision. A successor of a
revision is a later revision that has the revision as one of its
predecessors. Each revision except for the initial revision has at
least one predecessor.
The following diagram illustrates several of the previous
definitions.
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Versioned -------> Foo.htm
Resource
+----+ \
Initial Revision ---> | V1 | |
+----+ |
| |
| |
+----+ |
Label ------> "beta1" | V2 | |
+----+ |
/ \ |
/ \ |
+----+ +----+ |
Revision Id ------> V3 | | V4 | | History
+----+ +----+ | of
^ | | | Foo.htm
Predecessor | | | |
| +----+ +----+ |
| V5 | | V6 | |
+----+ +----+ |
| \ / |
Successor | \ / |
v +----+ |
| V7 | |
+----+ /
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Target
Whenever a server encounters a versioned resource while it is
processing an HTTP request, it acts on the "target" of the
versioned resource, rather than on the versioned resource itself.
This allows a client to largely ignore the fact that a resource has
been placed under version control. Workspace and Version-Selector
headers are used to control the target selection for a versioned
resource. The "default target" of a versioned resource is the
target selected when neither a Workspace nor a Revision-Selector
header is specified.
1.3 Notational Conventions
The augmented BNF used by this document to describe protocol
elements is exactly the same as the one described in Section 2.1 of
[RFC2068]. Because this augmented BNF uses the basic production
rules provided in Section 2.2 of [RFC2068], those rules apply to
this document as well.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in [RFC2119].
The term "protected" is placed in parentheses following the
definition of a property that cannot up updated with a PROPPATCH
request.
2 WEBDAV VERSIONING SEMANTICS
2.1 Creating and Modifying Versioned Resources
An unversioned resource that can be put under version control is
called a versionable resource. A versionable resource that is put
under version control is called a versioned resource.
A versioned resource must be checked out before it can be modified.
Checking out a versioned resource produces a new resource, called a
working resource. A working resource is a modifiable copy of the
revision, and is identical to an unversioned resource in all
respects other than that it is associated with a particular
revision of a particular versioned resource. It may be edited by
setting its properties or contents any number of times. When the
author is satisfied that the working resource is in a state that
should be retained in the versioned resource history, the author
checks in the working resource to create a new revision of the
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versioned resource. The revision that was checked out is the
predecessor of the new revision.
The following diagram illustrates the checkout/checkin process.
===CHECKOUT==> ===CHECKIN==>
Foo.htm | Foo.htm | Foo.htm
| |
+----+ | +----+ | +----+
| V1 | | | V1 | | | V1 |
+----+ | +----+ | +----+
| | | | |
v | v | v
+----+ | +----+ | +----+
| V2 | | | V2 | | | V2 |
+----+ | +----+ | +----+
| | | |
| v | v
| +----+ | +----+
| | WR | | | V3 |
| +----+ | +----+
The use of checkout/checkin and working resources to update a
versioned resource addresses the lost update problem by ensuring
that each author is updating his or her own working resource rather
than a shared resource, and by ensuring that the predecessor of the
updated resource is reliably tracked. Authors can use
checkout/checkin to register intent to modify a versioned resource
similar to the way lock /unlock are used in WebDAV class 2, but the
underlying semantics are very different. With lock/unlock, work is
serialized and avoiding lost updates depends on clients using the
lock/unlock protocol. With checkout/checkin, work can be performed
in parallel, and the server prevents lost updates by retaining all
saved states (revisions) of the resource. Another distinction is
that an update to a locked resource is immediately visible to all
clients, while an update to a working resource in a workspace is
immediately visible only to clients using that workspace.
A server MAY support mutable revisions. Normally, a revision cannot
be changed and provides a stable environment for history
management, change recovery, merging, and configuration management.
A mutable revision is more suitable for situations where versioning
is treated more informally, and it is not necessary or desirable to
maintain strict version histories, or to guarantee the possibility
of backtracking to a previous saved state. If mutable revisions are
supported, the author may request that a checkin should overwrite
the revision that was checked out, instead of creating a new
revision. In this case, the previous state captured by that
revision is lost. Servers may choose not to support mutable
revisions.
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2.2 Naming Working Resources: Workspaces
Workspaces are used to distinguish a working resource of a
versioned resource from other working resources of that versioned
resource. A working resource of a versioned resource is given a
server assigned workspace when it is created. This workspace acts
as an identifier that distinguishes this working resource from all
others of the same versioned resource. A workspace does not
distinguish working resources from different versioned resources,
since the same workspace can be assigned to a working resource of
any versioned resource.
2.3 Naming Revisions: Revision Ids and Revision Labels
Revision ids and revision labels are used to distinguish a revision
of a versioned resource from other revisions of that versioned
resource. A revision of a versioned resource is given a server
assigned revision id when it is created. This revision id acts as a
persistent, immutable identifier distinguishing this revision from
all others of the same versioned resource. The revision id cannot
be changed, assigned to another revision, or reused.
A user may assign revision labels to a revision in order to provide
a more meaningful name for the revision. A given revision label
can be assigned to at most one revision of a given versioned
resource, but may be reassigned to any other revision of the
versioned resource at any time.
Revision identifiers and revision labels are unique only across a
single versioned resource. That is, a revision id or revision
label does not distinguish revisions from different versioned
resources, since the same revision id or revision label can be
applied to a revision of any other versioned resource.
2.4 Accessing Versioned Resources: Workspace and Revision-Selector
Headers
When a method is applied to a versioned resource, it is applied to
the target of that versioned resource. The target can be a working
resource of the versioned resource, a revision of the versioned
resource, or the versioned resource itself. The Workspace and
Revision-Selector headers of the request determine the target. If
neither a Workspace or a Revision-Selector header is specified, the
target is the DAV:default-revision of the versioned resource.
3 VERSIONING PROPERTIES BY RESOURCE TYPE
This section defines the new resource types and properties
introduced by WebDAV versioning. When a property cannot be updated
by a PROPPATCH request, it is identified in this document as a
"protected" property.
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3.1 Common Property Values
3.1.1 boolean Syntax
Some properties take a Boolean value.
boolean = "F" | "T"
3.1.2 segment Syntax
Some properties take a value suitable for use as a segment of a
URI. Segment characters are encoded in UTF-8 format, and then when
appropriate escaped with the URL segment escaping mechanism defined
in section 3.3 of [RFC2396].
3.1.3 date-time Syntax
Some properties take a date or time value. The syntax of date-time
is defined in section 23.2 of [RFC2518].
3.1.4 href XML Element
The href XML element is defined in section 12.3 of [RFC2518].
3.1.5 stable href
A stable href contains a URL that identifies a resource that cannot
be renamed with a MOVE request.
3.2 Resource Properties
WebDAV versioning introduces the following properties for a
resource:
3.2.1 DAV:author
This property is used to track the author of a resource. Different
revisions of a versioned resource can have different DAV:author
values, indicating who authored that revision.
<!ELEMENT author (#PCDATA)>
3.2.2 DAV:comment
This property is used to track a brief comment about a resource.
Each revision of a versioned resource has its own set of
properties, so each revision can be given a DAV:comment appropriate
to that revision.
<!ELEMENT comment (#PCDATA)>
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3.3 Versioned Resource Properties
The DAV:resourcetype of a versioned resource MUST be DAV:versioned-
resource-resourcetype. WebDAV versioning introduces the following
properties for a versioned resource:
3.3.1 DAV:revision-set (protected)
This property identifies the revisions of this versioned resource.
Each DAV:revision-set href contains a stable URL.
<!ELEMENT revision-set (href*)>
3.3.2 DAV:initial-revision (protected)
This property identifies the initial revision of this versioned
resource. The DAV:initial-revision href contains a stable URL.
<!ELEMENT initial-revision (href)>
3.3.3 DAV:default-revision
This property identifies the default revision of this versioned
resource that will be the target of the versioned resource if no
Workspace or Revision-Selector header is specified. Whenever a new
revision is created by the automatic CHECKIN resulting from
automatic versioning (see the DAV:auto-version property), the
DAV:default-revision property is updated to refer to that revision
. The DAV:default-revision href contains a stable URL.
<!ELEMENT default-revision (href)>
3.3.4 DAV:auto-version
When the DAV:auto-version property of a versioned resource is set,
a request that attempts to modify the state of a revision of that
versioned resource without specifying a Workspace or Revision-
Selector header (such as PUT/PROPPATCH for a basic resource or a
DELETE /MOVE for a collection) is automatically preceded by a
CHECKOUT and automatically followed by a CHECKIN. This allows a
versioning-unaware client to modify a version-controlled resource.
<!ELEMENT auto-version (boolean)>
3.4 Revision Properties
WebDAV versioning introduces the following properties for a
revision of a versioned resource:
3.4.1 DAV:revision-id (protected)
The DAV:revision-id is an identifier assigned to a revision by the
server. A revision cannot be given a DAV:revision-id that has been
given to any other revision of that versioned resource, even a
revision that has been deleted.
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<!ELEMENT revision-id (#PCDATA)>
Value: segment
Since implementations are likely to use revision ids in resource
naming schemes, a revision id is constrained to be a legal URL
segment. Standard URL encoding techniques should provide a server
with sufficient flexibility in defining revision id formats.
Since a revision id can be specified in a Revision-Selector header,
the length of a revision id should be compatible with common header
length constraints.
3.4.2 DAV:revision (protected)
This property contains a stable URL for this revision. This is a
server allocated URL that can be used without a Revision-Selector
header to reference this revision. The DAV:revision href contains
a stable URL.
<!ELEMENT revision (href)>
3.4.3 DAV:predecessor-set (protected)
The DAV:predecessor-set of a revision identifies the revision that
was checked out to produce this revision. The DAV:predecessor-set
property can identify multiple revisions if the advanced versioning
MERGE method is supported. Each DAV:predecessor-set href contains a
stable URL.
<!ELEMENT predecessor-set (href*)>
3.4.4 DAV:successor-set (protected)
This property identifies the revisions whose DAV:predecessor-set
identify this revision. Each DAV:successor-set href contains a
stable URL.
<!ELEMENT successor-set (href*)>
3.4.5 DAV:label-set (protected)
This property is used to identify labels that are associated with a
specific revision. The value of DAV:label-set is updated with the
LABEL method.
<!ELEMENT label-set (label*)>
<!ELEMENT label (#PCDATA)>
Value: segment
Since revision labels are only exposed to a user as a simple
mnemonic tag for selecting a specific revision, embedding advanced
XML facilities for character set tagging, character set encoding,
and language tagging would not be appropriate. For label
applications that are not exposed to a user, the standard URL
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encoding techniques will provide a client with sufficient
flexibility in defining label formats.
Since a revision label can be specified in a Revision-Selector
header, clients should limit the length of a revision label to be
compatible with common header length constraints.
3.4.6 DAV:checkin-date (protected)
This property contains the date when the revision was checked in.
<!ELEMENT checkin-date (#PCDATA)>
Value: date-time
3.4.7 DAV:workspace-set (protected)
This property identifies the workspaces for the working-resources
currently checked out from this revision. Each DAV:workspace-set
href contains a stable URL. This property is updated with the
CHECKOUT method.
<!ELEMENT workspace-set (href*)>
3.4.8 DAV:single-checkout
When the DAV:single-checkout property of a revision is true, only
one working resource can be checked out from that revision at any
time.
<!ELEMENT single-checkout (#PCDATA)>
Value: boolean
3.4.9 DAV:versioned-resource (protected)
This property identifies the versioned resource that contains this
revision. The DAV:versioned-resource href contains a stable URL.
<!ELEMENT versioned-resource (href)>
3.5 Working Resource Properties
WebDAV versioning introduces the following properties for a working
resource:
3.5.1 DAV:workspace (protected)
This property identifies the workspace for this working resource.
The DAV:workspace href contains a stable URL.
<!ELEMENT workspace (href)>
3.5.2 DAV:predecessor-set (protected)
This property identifies the revision that was checked out to
create this working resource. Each DAV:predecessor-set href
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contains a stable URL. The advanced versioning MERGE method can be
used to add additional values to this property.
<!ELEMENT predecessor-set (href*)>
3.5.3 DAV:checkin-policy
The DAV:checkin-policy property of a working resource describes any
special processing that should be performed when this working
resource is checked in. If a PROPPATCH request specifies a
DAV:checkin-policy that is not supported by the server, it MUST
fail. The following are defined values for DAV:checkin-policy:
DAV:new-revision - Create a new revision (the default value).
DAV:overwrite - The working resource should be copied into its
DAV:predecessor instead of creating a new revision. This CHECKIN
will succeed only if the server supports mutable revisions.
DAV:keep-checked-out - Create a new revision but do not delete the
working resource. The DAV:predecessor-set of the working resource
is changed to identify the new revision.
<!ELEMENT checkin-policy
(new-revision | overwrite | keep-checked-out | ANY)* >
<!ELEMENT new-revision EMPTY>
<!ELEMENT overwrite EMPTY>
<!ELEMENT keep-checked-out EMPTY>
4 VERSIONING AND EXISTING METHODS
For most existing HTTP and WebDAV methods, the only change
introduced by versioning is instead of applying a method to a
versioned resource, the method is applied to the target of that
versioned resource. Note that if a method modifies only a binding
to a resource and not the resource itself (e.g. DELETE, MOVE,
BIND), the method is being applied to the collection containing
that binding, so these methods are not affected by versioning
unless that collection is under version control.
4.1 Automatic Versioning for Versioning Unaware Clients
For methods that update a resource (e.g. PUT, PROPPATCH), when that
method is applied to a revision of a versioned resource, the method
MUST fail unless the versioned resource has a DAV:auto-version
property and no Workspace or Revision-Selector header has been
specified. In this case, the revision is checked out, the update
is applied to the resulting working resource, and the working
resource is checked in. The check-out, update, check-in sequence
MUST be performed atomically. This functionality allows a
versioning unaware client to update a versioned resource.
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4.2 New Status Codes for Existing Methods
4xx (No Such Revision): The selected versioned resource does not
have the specified revision.
4xx (No Such Working Resource): The selected versioned resource
does not have the specified working resource.
5 NEW WEBDAV METHODS
WebDAV versioning introduces two new methods, MKRESOURCE and
REPORT, which are not specific to versioning but are needed to
support the versioning extensions.
5.1 MKRESOURCE
The MKRESOURCE method requests the creation of a resource and
initialization of its properties. It allows resources other than
standard data containers and collections to be created and their
properties initialized in one atomic operation.
Preconditions:
A resource MUST NOT exist at the Request-URL.
Request Marshalling:
The location of the new resource to be created is specified by the
Request-URL.
The request body of the MKRESOURCE method MUST consist of the
DAV:propertyupdate XML element defined in Section 12.13 of
[WebDAV].
Postconditions:
If the response status code is 201, a new resource exists at the
request-URL.
The body of the new resource is empty.
The properties of the new resource are as specified by the
DAV:propertyupdate request body, using PROPPATCH semantics. If the
DAV:propertyupdate does not specify a DAV:resourcetype, the
resource will be a standard data container.
If the response status code is not 201, then a new resource is not
created at the request-URL, and any existing resource at the
request-URL is unaffected.
Response Marshalling:
Responses from a MKRESOURCE request SHOULD NOT be cached, as
MKRESOURCE has non-idempotent semantics.
The following status codes can be expected in responses to
MKRESOURCE request:
201 (Created): The new resource was successfully created.
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207 (Multi-Status): This response is generated if an error was
encountered while initializing the properties of the resource, in
which case the response is as defined in Section 8.2.1 of [WebDAV].
403 (Forbidden): The server does not allow the creation of the
requested resource type at the requested location, or the parent
collection of the request-URL exists but cannot accept members.
409 (Conflict): A resource cannot be created at the request-URL
because the parent collection for the resource does not exist, or
because there is already a resource at that request-URL.
423 (Locked): The request-URL is locked and the lock token was not
specified in the request.
507 (Insufficient Storage): The server does not have sufficient
space to record the state of the resource.
5.1.1 Example - MKRESOURCE
MKRESOURCE /repo/worspaces/public HTTP/1.1
Host: www.webdav.org
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:propertyupdate xmlns:D="DAV:">
<D:set>
<D:prop>
<D:resourcetype> <D:workspace-resourcetype/>
</D:resourcetype>
</D:prop>
</D:set>
</D:propertyupdate>
>>Response
HTTP/1.1 201 Created
Host: www.webdav.org
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
5.2 REPORT
The REPORT request is an extensible mechanism for obtaining
information about resources. This differs from OPTIONS in that the
information provided is dynamic. The REPORT method MUST not change
the state of any resource managed by the server.
This document defines two general purpose reports (DAV:available-
report, DAV:property-report) and two advanced versioning reports
(DAV:compare-report, DAV:conflict-report).
Request Marshalling:
The resource that is the target of the report is specified by the
request-URL.
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A Depth header MAY be specified.
The request body of the REPORT method MUST consist of a DAV:report-
request XML element.
Response Marshalling:
The response body of the REPORT method MUST consist of a
DAV:report-response XML element.
The following status codes can be expected in responses to REPORT
request:
200 (OK): Generated on successful completion of the requested
report. The body of the response is marshaled as a DAV:report-
response.
5.2.1 DAV:report-request
Describes a report request.
<!ELEMENT report-request
(available-report-request
| property-report-request
| conflict-report-request
| compare-report-request
| ANY)>
5.2.2 DAV:report-response
A DAV:report-response contains an entire report. A response can be
for one of the standard reports (reports, conflict, or compare) or
for a server-defined report. The form of server-defined requests
is not specified.
<!ELEMENT report-response status
(available-report-response
| property-report-response
| conflict-report-response
| compare-report-response
| ANY)>
5.3 Available REPORT
The list of reports supported by the resource identified by the
request-URL.
5.3.1 DAV:available-report-request
<!ELEMENT available-report-request EMPTY>
5.3.2DAV:available-report-response
A DAV:available-report-response is a sequence of elements
identifying the supported reports.
<!ELEMENT available-report-response
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(available-report
| property-report
| conflict-report
| compare-report
| ANY)*>
<!ELEMENT available-report EMPTY>
<!ELEMENT property-report EMPTY>
<!ELEMENT conflict-report EMPTY>
<!ELEMENT compare-report EMPTY>
5.3.3Example - Available REPORT
>>Request
REPORT /myCollection HTTP/1.1
Host: www.webdav.org
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
Workspace http://www.webdav.org/repo/workspaces/public
<?xml version="1.0" encoding="utf-8" ?>
<D:report-request xmlns:D="DAV:">
<D:available-report/>
</D:report-request>
>>Response
HTTP/1.1 200 OK
Host: www.webdav.org
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
Workspace http://www.webdav.org/repo/workspaces/public
<?xml version="1.0" encoding="utf-8" ?>
<D:report-response xmlns:D="DAV:">
<D:available-report-response>
<DAV:available-report/>
<DAV:conflict-report/>
</D:available-report-response>
</D:report-response>
5.4 Property REPORT
Many properties consist of a set of one or more href elements. The
property REPORT provides a mechanism for retrieving in one request
the properties from all of the resources identified by those href
elements.
5.4.1 DAV:property-report-request
<!ELEMENT property-report-request (property-list)>
<!ELEMENT property-list ...> (TBD)
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5.4.2DAV:property-report-response
TBD.
5.4.3Example - Property REPORT
>>Request
REPORT /myCollection HTTP/1.1
Host: www.webdav.org
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
Workspace http://www.webdav.org/repo/workspaces/public
<?xml version="1.0" encoding="utf-8" ?>
<D:report-request xmlns:D="DAV:">
<D:property-report-request>
...
</D:property-report-request>
</D:report-request>
>>Response
HTTP/1.1 200 OK
Host: www.webdav.org
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
Workspace http://www.webdav.org/repo/workspaces/public
<?xml version="1.0" encoding="utf-8" ?>
<D:report-response xmlns:D="DAV:">
<D:property-report-response>
...
</D:property-report-response>
</D:report-response>
6 VERSIONING METHODS
6.1 VERSION
The VERSION method can be applied to a versionable resource to
produce a new versioned resource whose initial revision is a copy
of the versionable resource.
Preconditions:
The request-URL MUST identify a versionable resource.
Request Marshalling:
The request-URL specifies a versionable resource.
Postconditions:
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A new versioned resource is created.
The initial revision of the new versioned resource is a copy of the
versionable resource.
The value of the DAV:resourceid of the initial revision is the same
as that of the versionable resource.
The versionable resource is replaced in its parent collection by
the new versioned resource.
Response Marshalling:
The response MUST contain a Location header containing a stable URL
for the new versioned resource.
The following status codes can be expected in responses to a
VERSION request:
201 (Created): The versioned resource was successfully created.
404 (Not Found): The request-URL did not identify a resource.
405 (Method Not Allowed): The selected resource is not a
versionable resource.
6.1.1Example - VERSION
>> REQUEST
VERSION /file HTTP/1.1
Host: www.webdav.org
>> RESPONSE
HTTP/1.1 201 Created
Host: www.webdav.org
Location: http://www.webdav.org/repository/example/vr/183
6.2 CHECKOUT
The CHECKOUT method can be applied to a URL whose target is a
revision to produce a working resource that is a modifiable copy of
that revision. The CHECKOUT response will contain a Workspace
header that can be used in subsequent requests on that URL to
identify that working resource. A CHECKIN request applied to
that working resource can be used to create a new revision of that
working resource.
Preconditions:
The request-URL MUST identify either a revision or a versioned
resource whose target is a revision. This is the "selected
revision". The versioned resource for the revision is the
"selected versioned resource".
If the DAV:single-checkout property of the selected revision is
set, this revision MUST not be already checked out.
Request Marshalling:
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The request-URL specifies the revision to check out.
If the request-URL identifies a versioned resource, the revision to
be checked out MAY be specified in a Revision-Selector header.
Postconditions:
A new working resource that is a copy of the revision is created.
The value of the DAV:resourceid of the working resource is the same
as that of the revision.
The DAV:predecessor-set of the new working resource is set to the
selected revision.
The DAV:workspace of the new working resource is set to a value
selected by the server. The value of DAV:workspace is the
"selected workspace".
The selected workspace is added to the DAV:workspace-set property
of the selected revision.
Response Marshalling:
Results from a CHECKOUT request MUST NOT be cached as CHECKOUT has
non-idempotent semantics.
The response MUST contain a Location header containing a stable URL
for the new working resource.
The following status codes can be expected in responses to a
CHECKOUT request:
201 (Created): The working resource was successfully created.
404 (Not Found): The request-URL did not identify a resource.
405 (Method Not Allowed): The selected resource is not a revision
or the specified Workspace is invalid.
409 (Conflict): Any other violated pre-condition of the CHECKOUT
request.
6.2.1Example - CHECKOUT
>> REQUEST
CHECKOUT /file HTTP/1.1
Host: www.webdav.org
>> RESPONSE
HTTP/1.1 201 Created
Host: www.webdav.org
Workspace: http://www.webdav.org/workspaces/ws-23
Location: http://www.webdav.org/workspaces/ws-23/wr/X143
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6.3 UNCHECKOUT
The UNCHECKOUT method can be applied to a working resource of a
versioned resource to cancel the CHECKOUT and delete the working
resource.
Preconditions:
The target of the request-URL MUST be a working resource.
Request Marshalling:
The request-URL specifies the working resource.
The Workspace header specifies the workspace that contains the
selected working resource. This workspace is the "selected
workspace".
Postconditions:
The selected working resource is removed from the selected
workspace.
Response Marshalling:
The following status codes can be expected in responses to an
UNCHECKOUT request:
200 (OK): The working resource was successfully deleted.
404 (Not Found): The request-URL did not identify a resource.
405 (Method Not Allowed): The selected resource is not a working
resource or the specified Workspace is invalid.
6.3.1Example - UNCHECKOUT
>> REQUEST
UNCHECKOUT /file HTTP/1.1
Host: www.webdav.org
Workspace: http://www.webdav.org/workspaces/mywksp
>> RESPONSE
HTTP/1.1 200 OK
Host: www.webdav.org
Workspace: http://www.webdav.org/workspaces/mywksp
6.4 CHECKIN
The CHECKIN method can be applied to a working resource of a
versioned resource to produce a new revision that is a copy of that
working resource. This working resource is the "selected working
resource". The DAV:predecessor-set of the selected working
resource identifies the "predecessor revisions". The versioned
resource that contains the predecessor revisions is the "selected
versioned resource". The DAV:workspace property of the working
resource is the "selected workspace". If the server supports
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mutable revisions and there is a single predecessor revision, then
CHECKIN can be used to overwrite the value of the predecessor
revision.
Preconditions:
The request-URL MUST identify a working resource.
Request Marshalling:
The request-URL specifies the working resource.
The Workspace header specifies the workspace that contains the
selected working resource.
If a request body is specified, it MUST contain a DAV:checkin-
policy XML element.
Postconditions:
A new revision is created for the selected versioned resource. The
new revision is a copy of the working resource without the
DAV:checkin-policy property.
The value of the DAV:resourceid of the new revision is the same as
that of the working resource.
The selected workspace is deleted from the DAV:workspace-set
property of the predecessor revisions.
The new revision is added to the DAV:successor-set property of the
predecessor revisions.
If DAV:keep-checked-out is specified, the working-resource is not
deleted, but the DAV:predecessor-set property of the working
resource is modified to contain just the new revision. Otherwise,
the selected working resource is deleted.
Response Marshalling:
The response MUST contain a Location header containing a stable URL
for the new revision.
The following status codes can be expected in responses to a
CHECKIN request:
201 (Created): The revision was successfully created.
404 (Not Found): The request-URL did not identify a resource.
405 (Method Not Allowed): The selected resource is not a working
resource, the specified Workspace is invalid, or the specified
properties in the DAV:propertyupdate element are invalid.
409 (Conflict): Any other violated pre-condition of the CHECKIN
request.
6.4.1Example - CHECKIN
>> REQUEST
CHECKIN /file HTTP/1.1
Host: www.webdav.org
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Workspace: http://www.webdav.org/workspaces/mywksp
Content-type: text/xml; charset="utf-8"
<? xml version="1.0" encoding="utf-8" ?>
<D:checkin-policy> <D:keep-checked-out/> </D:checkin-policy>
>> RESPONSE
HTTP/1.1 201 Created
Host: www.webdav.org
Workspace: http://www.webdav.org/workspaces/mywksp
Content-type: text/xml; charset="utf-8"
Location: http://www.webdav.org/repository/vr/23/rev/12
6.5 LABEL
The LABEL method is used to add or remove a label on a revision of
a versioned resource.
Preconditions:
The request-URL MUST identify a revision of a versioned resource.
Request Marshalling:
The request-URL specifies the revision.
The body of the request contains either a DAV:add or a DAV:delete
element.
Postconditions:
The specified label has been added to or deleted from the specified
revision.
Response Marshalling:
The following status codes can be expected in responses to a LABEL
request:
200 (OK): The label update was performed.
400 (Bad Request): The specified label was not a legal segment.
404 (Not Found): The request-URL did not identify a resource.
405 (Method Not Allowed): The selected resource is not a revision.
6.5.1Example - LABEL
>> REQUEST
LABEL /file HTTP/1.1
Host: www.webdav.org
Workspace "http://www.webdav.org/workspaces/mywksp"
Content-type: text/xml; charset="utf-8"
<?xml version="1.0" encoding="utf-8" ?>
<D:add>stable</D:add>
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>> RESPONSE
HTTP/1.1 200 OK
Host: www.webdav.org
Workspace "http://www.webdav.org/workspaces/mywksp"
Content-type: text/xml; charset="utf-8"
7 VERSIONING HEADERS
7.1 Workspace
The following defines the BNF for the Workspace header:
Workspace := "Workspace" ":" URL
| "Workspace" ":"
The syntax of a URL is defined in [RFC2396].
Examples of a workspace header are:
Workspace: http://www.webdav.org/workspaces/public
Workspace:
Whenever a server encounters a versioned resource while it is
processing an HTTP request, it is required to act on the target of
the versioned resource. The Workspace header specifies which
workspace will be used to determine the target. If that workspace
identifies a working resource for that versioned resource, that
working resource is selected; otherwise, the request MUST fail.
If the Workspace-URL is omitted in the Workspace header, the
versioned resource itself is the target of the request. This allows
a client to access the properties of the versioned resource itself.
If no Workspace header is specified, the DAV:default-revision of
that versioned resource is selected.
A server MUST return a Vary header containing "Workspace" in any
response that includes a Workspace header.
7.2 Revision-Selector
The following defines the BNF for the Revision-Selector header:
Revision-Selector
:= "Revision-Selector" ":" "id" segment
| " Revision-Selector" ":" "label" segment
Examples of a Revision-Selector header are:
Revision-Selector: id Rev178AE8
Revision-Selector: label released
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When the target of a request-URL would otherwise be a working
resource or a revision of a versioned resource, a Revision-Selector
header causes the revision identified by the specified id or label
to be selected instead.
A server MUST return a Vary header containing "Revision-Selector"
in any response that includes a Revision-Selector header.
8 ADVANCED VERSIONING
8.1 Advanced Versioning Terms
Workspace
A workspace is a resource that not only identifies working
resources, but also contains a revision selection rule that
specifies what revision of an arbitrary versioned resource should
be accessed when the resource is referenced in the context of that
workspace. A revision selection rule provides revision selection
based on criteria such as revision label, latest in an activity,
and membership in a configuration.
The following diagram illustrates a workspace resource.
Foo.htm Bar.htm Bing.htm
+----+ +----+
| V1 | | V1 |
+----+ +----+
| |
| |
+-----------------|------------|------------------+
| v v |
| +----+ +----+ +----+ |
| | V1 | | V2 | | WR | Workspace X |
| +----+ +----+ +----+ |
| | |
+-----------------|-------------------------------+
|
v
+----+
| V3 |
+----+
Default Workspace
A default workspace can be associated with a collection to specify
the default revision selection for members of that collection .
The revision selection specified by a default workspace overrides
the DAV:default-revision property of a versioned resource.
Activity
An activity is a resource that selects a set of revisions that
correspond to some unit of work or conceptual change. An activity
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can contain revisions of multiple versioned resources, and multiple
revisions of the same versioned resource. If an activity contains
multiple revisions of the same versioned resource, every revision
must be on a single "line of descent" in that versioned resource,
where a line of descent is a sequence of revisions connected by
successor relationships.
The following diagram illustrates activities. Revision V3 is the
latest revision of Foo.htm selected by activity 2, and revision V7
is the latest revision of Bar.htm selected by activity 2.
Foo.htm | Bar.htm
|
+----+ | +----+
| V1 | | | V5 |
+----+ | +----+
| Activity | | Activity
v 1 | v 2
+----+ | +----+
| V2 | | | V6 |
+----+ | +----+
| Activity | | Activity
v 2 | v 2
+----+ | +----+
| V3 | | | V7 |
+----+ | +----+
| | Activity
| v 3
| +----+
| | V8 |
| +----+
Conflict Report
A conflict report lists all versioned resources for which the
revision selection rule of a workspace selects multiple revisions
on different lines of descent. A conflict is resolved by checking
out one of the selected revisions, modifying the resulting working
resource so that it represents the logical merge of all selected
revisions, and then indicating these merges by adding these
revisions as additional predecessors of the working resource.
Checking in this working resource creates a new revision that
resolves the conflict.
Configuration
A configuration is a type of collection that contains a set of
revisions, with a most one revision from any versioned resource.
Unlike a workspace, which can select both working resources and
revisions, a configuration can only select revisions. Also, while
the revision selected by a workspace for a versioned resource can
change as a result of a change to the versioned resource (such as
adding a label), the revision selected by a configuration can
change only by explicitly modifying the configuration. Unlike an
activity, a configuration can contain at most one revision of a
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given versioned resource. Unlike both a workspace and an activity,
a configuration can be versioned.
The following diagram illustrates a configuration.
Foo.htm Bar.htm Bing.htm
+----+
| V1 |
+----+
|
|
+-----------------|-------------------------------+
| | |
| +----+ +----+ +----+ Configuration |
| | V1 | | V2 | | V1 | V1.1 |
| +----+ +----+ +----+ |
| | | |
+-----------------|------------|------------------+
| |
v v
+----+ +----+
| V3 | | V2 |
+----+ +----+
Versioned Collection
A versioned collection is a type of versioned resource that results
from placing a collection under version control. The members of a
versioned collection revision must be versioned resources. The
working resource that results from checking out a versioned
collection is called a working collection.
Baseline
A baseline is a revision of a versioned configuration that is
associated with a particular versioned collection. Each baseline
defines a "deep revision" of a particular versioned collection. A
deep revision of a versioned collection captures the state of a
versioned collection in a particular workspace, including a
revision of the versioned collection selected by that workspace, as
well as a revision of every member of that versioned collection
selected by that workspace.
Repository
A repository is a type of resource that contains related versioned
resources, activities, and configurations. A repository provides a
stable namespace for versioning metadata resources, and provides
versioning unaware clients access to the versioning metadata.
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9 ADVANCED VERSIONING SEMANTICS
9.1 Revision Selection and Workspaces
When a request URL identifies a versioned resource, it is necessary
to provide additional information to specify which working resource
or which revision of the versioned resource should be accessed.
Specifying the resource URL and a revision label can access a
specific revision of the versioned resource. However, this
requires the user to add and remember labels for each revision; it
does not provide a way of accessing a consistent set of revisions
captured by an activity or contained in a configuration; it does
not enable non-versioning aware clients to access revisions; and it
does not provide a client with access to a working resource of a
versioned resource.
To address the restrictions inherent in revision-name based
revision selection, the revision selected when a specific revision
name is not specified is resolved through a workspace. A workspace
is a resource whose primary purpose is to identify working
resources. If the workspace contains no working resource for a
given versioned resource, it can also be used to select an
appropriate revision of the versioned resource. This allows
versioned resources and unversioned resources to be accessed
consistently by both versioning-aware and versioning-unaware
clients.
In order to specify revision selection, a workspace contains a
revision selection rule. A revision selection rule can specify
revision labels, activities, configurations, or use operators that
combine several of these revision selectors. A revision label
selects a revision with that label. An activity selects the latest
revision that was created in that activity. Configurations select
the revision contained in the configuration. The "or" operator
contains a sequence of rule elements, and applies them in order
until the first match is found. If there is no matching revision,
then a resource-not-found status is returned.
If a request is made and no workspace is specified, a server
determined default workspace is used. This is the workspace used by
all versioning-unaware clients. A server MAY allow modifications to
the revision selection rule of the default workspace.
9.2 Parallel Development, Activities, and Merging
In a locking model, when a resource is locked for modifications by
one author, all other authors are supposed to respect that lock and
not work on a copy of that resource until the lock has been
released. To avoid the work serialization inherent in the locking
model, a versioning model allows multiple authors in different
workspaces to check out the same revision at the same time, work on
their respective working resources in parallel, and check in their
respective working resources as soon as their changes are complete.
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This results in two parallel revisions (neither revision is an
ancestor of the other) that will need to be merged.
Although a simple versioning model works well for isolated changes
to independent resources, the required merge process becomes
unmanageable when sequences of inter-related changes are performed
on sets of related resources. To address this merge problem,
resources can be checked out in the context of an activity. An
activity captures the set of revisions that form a set of related
changes an author is making to one or more versioned resources.
Each activity represents a thread of development, where any thread
can be isolated from other threads to provide a stable environment
for parallel work.
When parallel work on isolated activities results in branches in
the underlying versioned resource histories, the activities can be
unified through a merge operation. The activities to be merged are
specified with a merge operator in the revision selection rule of a
workspace. A conflict report is then obtained from the workspace,
which enumerates which revisions of which versioned resources need
to be merged. The client then uses the conflict report to iterate
through the versioned resources that require merging, preferably
providing the user with some domain specific merge tool. Finally,
the result of each merge is checked in as a new revision with
multiple predecessors (the revisions that were merged). The next
time a conflict report is requested for that set of activities, the
workspace will indicate that no conflicts exist (i.e. all conflicts
have been resolved by merges).
9.3 Configurations
A workspace selects a volatile set of revisions. Changes to
selected activities or changes to labels may result in the
selection of different revisions. A configuration is a resource
that selects a specific set of revisions. A workspace whose
version selection rule contains a configuration will always select
the same revisions as long as the configuration is not modified and
no checkouts are performed in that workspace.
Configurations are convenient for defining a persistent set of
revisions that relate to each other in some specific way at some
point in time. This can be useful for a variety of purposes such as
publishing consistent versions of resources to deploy an
application, or for recovering a specific state for legal or
maintenance reasons.
9.4 Versioned Collections
A collection contains a set of named bindings to other resources
that are the members of that collection. For a versioned
collection, the bindings are to versioned resources, not to
particular revisions. To modify the state of a versioned collection
(i.e. add or remove a binding), the versioned collection must be
checked out, just like any other versioned resource. Requests that
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modify the state of a collection member, such as checking it out or
checking in a new revision, have no effect on the state of the
collection. Conversely, requests that modify the state of a
versioned collection, such as deleting or adding a binding to a
resource, have no effect on the state of that resource. In
particular, the resource will remain bound in any other revisions
of the collection of which it was a member.
It is often important to capture the entire tree of revisions
selected by a workspace rooted at a given versioned collection.
This "deep revision" of a versioned collection is called a
baseline.
If a URL identifies a sequence of nested versioned collections,
revision selection is performed for each versioned collection in
the sequence, to select the versioned collection revision that will
be used to map the next segment of the URL to the appropriate
versioned resource.
9.5 Repositories
A repository contains versioned resources, activities, and
configurations. Since a server will often allow certain metadata
relationships to be created only between resources in the same
repository, it is important to allow a client to specify in which
repository a resource should be created.
10 ADVANCED VERSIONING PROPERTIES BY RESOURCE TYPE
This section defines the new resource types and properties
introduced by WebDAV versioning.
10.1 Collection Properties
WebDAV advanced versioning introduces the following properties for
a collection:
10.1.1 DAV:default-workspace
This property of a collection identifies the workspace that should
be used to perform default revision selection for members of a
collection. The DAV:default-workspace href contains a stable URL.
<!ELEMENT default-workspace (href)>
10.2 Versioned Resource Properties
WebDAV advanced versioning introduces the following properties for
a versioned resource:
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10.2.1 DAV:baselines (protected)
This property appears on a versioned collection that has baselines.
It identifies the versioned configuration containing those
baselines. The DAV:baselines href contains a stable URL.
<!ELEMENT baselines (href)>
10.2.2 DAV:repository (protected)
This property identifies the repository that contains this
versioned resource. The DAV:repository href contains a stable URL.
<!ELEMENT repository (href)>
10.3 Revision Properties
WebDAV advanced versioning introduces the following properties for
a revision:
10.3.1 DAV:activity
This property identifies the activity that represents the logical
change to which this revision contributes. The DAV:activity href
contains a stable URL.
<!ELEMENT activity (href)>
10.4 Working Resource Properties
WebDAV advanced versioning introduces the following properties for
a working resource:
10.4.1 DAV:activity
This property identifies the activity that represents the logical
change to which this working resource contributes. The
DAV:activity href contains a stable URL.
<!ELEMENT activity (href)>
10.5 Workspace Properties
The DAV:resourcetype of a workspace MUST be DAV:workspace-
resourcetype. WebDAV advanced versioning introduces the following
properties for a workspace:
10.5.1 DAV:working-resource-set (protected)
This property identifies the working resources that are checked out
into this workspace. Each DAV:working-resource-set href contains a
stable URL.
<!ELEMENT working-resource-set (href*)>
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10.5.2 DAV:revision-selection-rule
If there is no working resource in a workspace for a given
versioned resource, the DAV:revision-selection-rule of the
workspace specifies the revision of that versioned resource that is
selected by that workspace. Since the working resources checked out
into a workspace take priority over revisions selected by the
revision selection rule, the target of a versioned resource in a
workspace is the working resource in that workspace for that
versioned resource, otherwise the revision selected by the
workspace revision selection rule. To ensure that working resources
continue to be visible in a workspace after they are checked in,
the DAV:current-label or DAV:current-activity of a workspace is
usually the first element of the DAV:revision-selection-rule. If
the DAV:revision-selection-rule is not set or is empty, the
workspace will select no revision for any versioned resource.
The DAV:revision-selection-rule property contains an XML element.
Semantically, a revision selection rule (or RSR) element can be
applied to an arbitrary versioned resource, and will either select
a particular revision of that versioned resource, select no
revision of that versioned resource, or detect a conflict (e.g.
when there were multiple candidates for selection). A document
describing the conflicts can be obtained through a conflict REPORT
request.
<!ELEMENT revision-selection-rule
(href | label | rsr-latest | rsr-or | rsr-merge)>
<!ELEMENT rsr-latest EMPTY>
<!ELEMENT rsr-or (href | label)*>
<!ELEMENT rsr-merge (href | label)*>
An href element contains a stable URL of an activity, a
configuration, or a revision.
If the href identifies an activity, and the DAV:revision-set
property of the activity contains one or more revisions of the
versioned resource, then the latest revision for that activity is
selected. The semantics of activities ensures that there always is
a unique latest revision for an activity. If the activity contains
no revisions of the versioned resource, the activity selects no
revisions of that versioned resource. If the DAV:needed-activity-
set property of an activity is non-empty, then the activity acts
like a DAV:rsr-merge element that contains that activity and each
of the DAV:needed-activity-set activities. An activity element can
generate conflicts only if the DAV:needed-activity-set property is
non-empty.
If the href identifies a configuration, and the configuration
contains a revision of the versioned resource, that revision is
selected by the configuration; otherwise, no revision is selected.
To avoid revision selection circularities, a versioned
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configuration MUST not be specified in a revision selection rule,
but a configuration revision may. A configuration never generates
a conflict.
If the href identifies a revision, then that revision is selected
if it is a revision of the versioned resource; otherwise, no
revision is selected.
If the revision selection rule element is a label, and a revision
of the versioned resource has that label, that revision is
selected; otherwise, no revision is selected. A label element
never generates a conflict.
A DAV:rsr-latest element selects the revision of that versioned
resource with the latest DAV:creationdate. A DAV:rsr-latest
element never generates a conflict.
A DAV:rsr-or element contains a sequence of RSR elements. The
behavior of a DAV:rsr-or element is identical to the behavior of
the first element in this sequence that selects a revision of the
versioned resource. If this element generates a conflict, the
DAV:rsr-or element generates this conflict as well. If no element
selects a revision, then the DAV:rsr-or element selects no revision
of that versioned resource.
A DAV:rsr-merge element contains a sequence of RSR elements. If
one of the elements in this sequence selects a revision that is the
descendent of all of the other revisions selected by elements in
this sequence, then that revision is selected by the DAV:rsr-merge
element. If no selected revision is a descendent of all the other
selected revisions, then the result of the DAV:rsr-merge is a
"conflict". A conflict REPORT request can be used to identify the
conflicts.
10.5.3 DAV:no-checkout
The DAV:no-checkout property of a workspace indicates that no new
working resources can be created in that workspace.
<!ELEMENT no-checkout (#PCDATA)>
Value: boolean
10.5.4 DAV:current-label
The DAV:current-label property of a workspace can contain a
revision label. When a working resource in a workspace is checked
in, it will be given this label.
<!ELEMENT current-label (#PCDATA)>
Value: segment
10.5.5 DAV:current-activity
The DAV:current-activity property of a workspace is the activity
that is currently being performed in that workspace. A new
working resource in a workspace will have its DAV:current-activity
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property set to this activity. The DAV:current-activity href
contains a stable URL.
<!ELEMENT current-activity (href)>
10.6 Activity Properties
The DAV:resourcetype of an activity MUST be DAV:activity-
resourcetype. WebDAV advanced versioning introduces the following
properties for an activity:
10.6.1 DAV:revision-set (protected)
This property identifies the revisions whose DAV:activity property
identifies this activity. Each DAV:revision-set href contains a
stable URL.
<!ELEMENT revision-set (href*)>
10.6.2 DAV:needed-activity-set
This property identifies the other activities that form a part of
the logical change being captured by this activity. The
DAV:needed-activity-set of an activity contribute to the revision
selection behavior of that activity when it is used in a revision
selection rule. The purpose of this property is to identify other
activities that are a prerequisite to this activity. Each
DAV:needed-activity-set href contains a stable URL.
<!ELEMENT needed-activity-set (href*)>
10.6.3 DAV:workspace-set (protected)
This property identifies the workspaces whose DAV:current-activity
property identifies this activity. Each DAV:workspace-set href
contains a stable URL.
<!ELEMENT workspace-set (href*)>
10.7 Configuration Properties
The DAV:resourcetype of a configuration MUST be DAV:configuration-
resourcetype.
10.7.1 DAV:baseline-root (protected)
This property appears on a configuration that is a baseline of a
versioned collection. It contains a stable URL to the versioned
collection.
<!ELEMENT baseline-root (href)>
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10.8 Repository Properties
The DAV:resourcetype of a repository MUST be DAV:repository-
resourcetype. WebDAV advanced versioning introduces the following
properties for a repository:
10.8.1 DAV:versioned-resource-collection (protected)
This property identifies the stable URL of a collection that
contains the set of versioned resources maintained by the
repository. The name of a versioned resource in this collection
MUST be its DAV:resourceid. This restricts the DAV:resourceid of a
versioned resource in a repository to be a legal URL segment.
<!ELEMENT versioned-resource-collection (href)>
10.8.2 DAV:repository-root (protected)
This property identifies the member of DAV:versioned-resource-
collection that can be exposed with a BIND operation in another
part of the URL namespace. The DAV:repository-root href contains a
stable URL.
<!ELEMENT repository-root (href)>
10.8.3 DAV:activity-collection (protected)
This property identifies the stable URL of a collection that
contains the set of activities maintained by that repository. New
activities can be added to this collection with a MKRESOURCE
request. A server MAY restrict the creation of new activities to
only occur in a DAV:activity-collection of a repository.
<!ELEMENT activity-collection (href)>
10.8.4 DAV:configuration-collection (protected)
This property identifies the stable URL of a collection that
contains the set of configurations maintained by that repository.
New configurations can be added to this collection with a
MKRESOURCE request. A server MAY restrict the creation of new
configurations to only occur in a DAV:configuration-collection
collection of a repository.
<!ELEMENT configuration-collection (href)>
11 ADVANCED VERSIONING AND EXISTING METHODS
Each binding in a working collection MUST be to a versioned
resource. Therefore, when a request (e.g. PUT, MKCOL, MKRESOURCE)
attempts to create a new resource in a working collection:
- a new versioned resource is created,
- an empty initial revision is created and checked out,
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- the request is used to initialize the state of the new working
resource,
- and a binding to the new versioned resource is added to the
working collection.
When a request attempts to add a binding to a revision of a
versioned collection, the request MUST fail unless the versioned
collection has a DAV:auto-version property and no Workspace header
has been specified. In this case, the versioned collection is
checked out, the request is applied to the resulting working
collection, and the working collection is checked in.
11.1LOCK
If a LOCK is successfully applied to a URL, revision selection in
the current workspace is frozen for the duration of the lock for
any versioned resource or versioned collection identified by that
URL or by any slash-terminated prefix of that URL. When revision
selection is frozen for a particular versioned resource in a
workspace, only a CHECKIN of a working resource in that workspace
for that versioned resource causes revision selection to be
recomputed for that versioned resource.
11.2CHECKOUT
When workspace resources are provided, a CHECKOUT request may
specify a workspace in the Workspace request header. The server
MUST use this workspace to identify the working resource created by
the CHECKOUT. If there already is a working resource for that
versioned resource with that workspace, the CHECKOUT request MUST
fail.
The new working resource is added to the DAV:working-resource-set
property of the selected workspace.
If the DAV:current-activity property of the specified workspace is
set, the DAV:activity property of the working resource is set to
that activity.
11.3CHECKIN
If the DAV:current-label of the workspace is set, that label is
applied to the new revision created by the CHECKIN request. If the
DAV:activity property of the working resource being checked in
identifies an activity, the new revision created by the CHECKIN is
added to the DAV:revision-set property of that activity.
If CHECKIN is being applied to a baseline of a versioned
collection, then the current workspace must select a particular
revision of each member of that versioned collection. In
particular, there can be no conflicts and there can be no working
resources.
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12 ADVANCED VERSIONING REPORTS
12.1Conflict REPORT
A conflict report describes the conflicts in a specified workspace
for a specified resource or for all the members of a specified
versioned collection. Conflicts occur when the workspace revision
selection rule selects more than one revision of a particular
versioned resource, resulting in ambiguous revision selection. The
resource to test is specified by the request-URL. Conflicts are
checked in the workspace specified in the Workspace header. If the
Workspace header is not given, the default workspace is used.
Conflicts for all resources transitively reachable from the
request-URL are reported according to the value of the Depth
header. If the Depth header is not specified, the value infinity
is assumed. Conflicts in resources reachable only via a versioned
collection which is itself ambiguous are not reported.
12.1.1 DAV:conflict-report-request
<!ELEMENT conflict-report-request EMPTY>
12.1.2 DAV:conflict-report-response
A DAV:conflict-report-response contains a DAV:conflict element for
each versioned resource for which the workspace produced a
conflict.
<!ELEMENT conflict-report-response (conflict*)>
<!ELEMENT conflict (href, common-ancestor, contributor,
contributor+)>
<!ELEMENT common-ancestor (#PCDATA)>
Value: segment
<!ELEMENT contributor(#PCDATA)>
Value: segment
The DAV:conflict element contains the URL of a versioned resource
for which the revision selection rule generated a conflict, a
DAV:common-ancestor for the conflict, and two or more
DAV:contributor elements for the conflict.
The DAV:common-ancestor element identifies the revision id of a
revision that is a common ancestor of all the DAV:contributor
elements for a particular conflict.
The DAV:contributor element identifies the revision id of a
revision that is selected by an element of the revision selection
rule but that is not an ancestor of any of the other revisions
selected by the revision selection rule.
12.1.3 Example - Conflict REPORT
>>Request
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REPORT /myCollection HTTP/1.1
Host: www.webdav.org
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
Workspace http://www.webdav.org/repo/workspaces/public
<?xml version="1.0" encoding="utf-8" ?>
<D:report-request xmlns:D="DAV:">
<D:conflict-report-request/>
</D:report-request>
>>Response
HTTP/1.1 200 OK
Host: www.webdav.org
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
Workspace http://www.webdav.org/repo/workspaces/public
<?xml version="1.0" encoding="utf-8" ?>
<D:report-response xmlns:D="DAV:">
<D:conflict-report-response>
<D:conflict>
<D:href>http://www.webdav.org/repo/vr/vr732</D:href>
<D:common-ancestor>revisionid:3</D:common-ancestor>
<D:contributor>revisionid:5</D:contributor>
<D:contributor>revisionid:4</D:contributor>
</D:conflict>
</D:conflict-report-response>
</D:report-response>
12.2Compare REPORT
A compare REPORT identifies the differences between the resource
identified by the request-URL (base) and the resources specified in
the body of the request (targets). The comparison is carried out
transitively on any children of the resources according to the
value of the Depth header. If the Depth header is not specified,
the value infinity is assumed. Resources appearing in a target but
not in the base are described by DAV:added elements, resources
appearing in the base but not a target are described by DAV:deleted
elements, and resources appearing in both base and target but
having different states are described by DAV:changed elements.
Resource content comparison is not specified, though servers MAY
provide it.
12.2.1 DAV:compare-report-request
A DAV:compare- request contains the URL's of the resources to be
compared with the resource identified by the request URL.
<!ELEMENT compare-report-request (href*)>
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12.2.2 DAV:compare-report-response
A DAV:compare-report-response identifies the differences between
two resources. These differences are indicated by appropriate
DAV:added, DAV:deleted, and DAV:changed elements. For example, if
a DAV:compare-request is applied to two configurations, the
DAV:compare-report-response contains the revisions that are
selected by one configuration but not the other.
<!ELEMENT compare-report-response (added, deleted, changed)*>
<!ELEMENT added (href, ANY*)>
<!ELEMENT deleted (href, ANY*)>
<!ELEMENT changed (href, ANY*)>
A DAV:added element identifies something that appears in a
particular target resource but not in the base.
A DAV:deleted element identifies something that appears in the base
resource but not in a particular target.
A DAV:changed element identifies information that is in both the
base and the target but that has changed in some way. For example,
when two configurations are being compared, a DAV:changed element
can identify a versioned resource if the configurations select
different revisions of that versioned resource.
12.2.3 Example - Compare REPORT
>>Request
REPORT /myCollection HTTP/1.1
Host: www.foo.com
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
Depth: 1
<?xml version="1.0" encoding="utf-8" ?>
<D:report-request xmlns:D="DAV:">
<D:compare-report-request>
<href>http://www.foo.com/myOtherCollection</href>
</D:compare-report-request>
</D:report-request>
>>Response
HTTP/1.1 200 OK
Host: www.foo.org
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:report-response xmlns:D="DAV:">
<D:compare-report-response>
<D:added>
<href>http://www.foo.com/myOtherCollection</href>
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</D:added>
<D:added>
<href>http://www.foo.com/myOtherCollection/foo.html</href>
</D:added>
<D:deleted>
<href>http://www.foo.com/myCollection/bar.html</href>
</D:deleted>
</D:compare-report-response>
</D:report-response>
13 ADVANCED VERSIONING METHODS
13.1MERGE
The MERGE method can be applied to a working resource to add or
delete predecessors for that working resource.
Preconditions:
The request-URL MUST identify a working resource.
A revision being added to the predecessors of a working resource
MUST share a common ancestor with each of the other predecessors of
the working resource.
A revision being added to the predecessors of working resource MUST
not be an ancestor of one of the other predecessors of the working
resource.
A revision being deleted from the predecessors of a working
resource MUST be one of the predecessors of the working resource.
Request Marshalling:
The request-URL specifies the working resource.
The body of the request contains an XML document with DAV:add and
DAV:delete members.
Postconditions:
The predecessor revisions being added are members of the
DAV:predecessor-set property of the working resource.
The predecessor revisions being deleted are not members of the
DAV:predecessor-set property of the working resource.
Response Marshalling:
The following status codes can be expected in responses to a MERGE
request:
200 (OK): The predecessor update was performed..
404 (Not Found): The request-URL did not identify a resource.
405 (Method Not Allowed): The selected resource is not a working
resource or the specified Workspace is invalid.
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409 (Conflict): Any other violated pre-condition of the MERGE
request.
13.1.1 Example - MERGE
>> REQUEST
MERGE /file HTTP/1.1
Host: www.webdav.org
Workspace "http://www.webdav.org/workspaces/mywksp"
Content-type: text/xml; charset="utf-8"
<?xml version="1.0" encoding="utf-8" ?>
<D:request xmlns:D="DAV:">
<D:add>http://www.webdav.org/repo/vr/VR182/rev/5
</D:response>
>> RESPONSE
HTTP/1.1 200 OK
Host: www.webdav.org
Workspace "http://www.webdav.org/workspaces/mywksp"
Content-type: text/xml; charset="utf-8"
13.2CONFIGURE
The CONFIGURE method is used to add or remove a revision from a
configuration.
Preconditions:
The request-URL MUST identify a revision of a versioned resource.
Request Marshalling:
The request-URL specifies the revision.
The body of the request contains either a DAV:add or a DAV:delete
element, where the value of the element is an href of a
configuration.
Postconditions:
The specified revision has been added to or deleted from the
specified configuration.
Response Marshalling:
The following status codes can be expected in responses to a
CONFIGURE request:
200 (OK): The configuration update was performed.
400 (Bad Request): The body of the request did not contain a
DAV:add or DAV:delete element whose value was an href of a
configuration.
404 (Not Found): The request-URL did not identify a resource.
405 (Method Not Allowed): The selected resource is not a revision.
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13.2.1 Example - CONFIGURE
>> REQUEST
CONFIGURE /file HTTP/1.1
Host: www.webdav.org
Workspace "http://www.webdav.org/workspaces/mywksp"
Content-type: text/xml; charset="utf-8"
<?xml version="1.0" encoding="utf-8" ?>
<D:add>
<D:href> http://www.webdav.org/repository/cg/357 </D:href>
</D:add>
>> RESPONSE
HTTP/1.1 200 OK
Host: www.webdav.org
Workspace "http://www.webdav.org/workspaces/mywksp"
Content-type: text/xml; charset="utf-8"
13.3BASELINE
The BASELINE method can be applied to a versioned collection to
allow the creation of baselines for that versioned collection.
Preconditions:
The request-URL MUST identify a versioned collection. The
versioned collection MUST NOT have a DAV:baselines property.
Request Marshalling:
The request-URL specifies the versioned collection.
Postconditions:
The DAV:baselines property of the versioned collection identifies a
new versioned configuration that will contain the baselines for the
versioned collection.
Response Marshalling:
The response MUST contain a Location header containing a stable URL
for the new versioned configuration.
The following status codes can be expected in responses to a
BASELINE request:
201 (Created): The versioned configuration was successfully created
and associated with the versioned collection.
404 (Not Found): The request-URL did not identify a resource.
405 (Method Not Allowed): The selected resource is not a versioned
collection.
409 (Conflict): The versioned collection already has a
DAV:baselines property.
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13.3.1 Example - BASELINE
>> REQUEST
BASELINE /folder HTTP/1.1
Host: www.webdav.org
>> RESPONSE
HTTP/1.1 201 Created
Host: www.webdav.org
Location: http://www.webdav.org/repository/vr/237
14 ADVANCED VERSIONING HEADERS
Advanced versioning does not introduce any new headers, but the
semantics of the Workspace header is extended to take advantage of
the DAV:revision-selection-rule property of workspace resources.
14.1Workspace
If the Workspace header specifies the URL of an advanced versioning
workspace resource, and no working resource for that versioned
resource exists in that workspace, then the revision specified by
the DAV:revision-selection-rule property of the workspace is
selected.
15 INTERNATIONALIZATION CONSIDERATIONS
To be supplied.
16 SECURITY CONSIDERATIONS
To be supplied.
17 SCALABILITY
To be supplied.
18 AUTHENTICATION
Authentication mechanisms defined in WebDAV will also apply to
WebDAV Versioning.
19 IANA CONSIDERATIONS
This document uses the namespace defined by [RFC2518] for XML
elements. All other IANA considerations mentioned in [RFC2518]
also applicable to WebDAV Versioning.
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20 INTELLECTUAL PROPERTY
The following notice is copied from RFC 2026, section 10.4, and
describes the position of the IETF concerning intellectual property
claims made against this document.
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use other technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on
the IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances
of licenses to be made available, or the result of an attempt made
to obtain a general license or permission for the use of such
proprietary rights by implementers or users of this specification
can be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF
Executive Director.
21 ACKNOWLEDGEMENTS
This protocol is the collaborative product of the Delta-V design
team: Jim Amsden (IBM, DeltaV Chair), Geoffrey Clemm (Rational),
Bruce Cragun (Novell), David Durand (INSO), Chris Kaler
(Microsoft), Jeff McAffer (OTI), Bradley Sergeant (Merant), and Jim
Whitehead (UC Irvine). We would like to acknowledge the foundation
laid for us by the authors of the WebDAV and HTTP protocols upon
which this protocol is layered, and the invaluable feedback from
the WebDAV and DeltaV working groups.
22 INDEX
To be supplied.
23 REFERENCES
[RFC2026] S.Bradner, "The Internet Standards Process", Harvard,
1996, <http://www.ietf.org/rfc/rfc2026.txt>.
[RFC2068] R.Fielding, J.Gettys, J.C.Mogul, H.Frystyk, and
T.Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2068,
U.C. Irvine, DEC, MIT/LCS, 1997,
<http://www.ietf.org/rfc/rfc2068.txt >.
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[RFC2119] S.Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", Harvard, 1997,
<http://www.ietf.org/rfc/rfc2119.txt >.
[RFC2396] T.Berners-Lee, R.Fielding, L.Masinter, ôUniform Resource
Identifiers (URI): Generic Syntaxö, MIT/LCS, U.C. Irvine, Xerox,
1998, <http://www.ietf.org/rfc/rfc2396.txt>.
[RFC2518] Y. Goland, E.Whitehead, A.Faizi, S.R.Carter, D.Jensen,
"HTTP Extensions for Distributed Authoring - WEBDAV", Microsoft,
U.C.Irvine, Netscape, Novell, 1999
<http://www.ietf.org/rfc/rfc2518.txt>.
[Binding] J.Slein, E.Whitehead, J.Davis, G.Clemm, C.Fay,
J.Crawford, T.Chihaya, "WebDAV Bindings", Xerox, U.C.Irvine,
CourseNet, Rational, FileNet, DataChannel, 1999,
<http://www.ietf.org/internet-drafts/draft-ietf-webdav-binding-
protocol-01.txt>
[Goals] J.Amsden, C.Kaler, J.Stracke, "Goals for Web Versioning",
IBM, Microsoft, Netscape, 1999, <http://www.ietf.org/internet-
drafts/draft-ietf-webdav-version-goals-01.txt>
24 AUTHORS' ADDRESSES
Geoffrey Clemm
Rational Software
20 Maguire Road
Lexington, MA
Email: geoffrey.clemm@rational.com
Christopher Kaler
Microsoft
One Microsoft Way
Redmond WA, 9085-6933
Email: ckaler@microsoft.com
25 OPEN ISSUES
The following list identifies key open issues against this
document:
@ TODO: Flesh out the effect of VERSION and CHECKIN on all
properties.
@ TODO: Add error conditions for auto-versioning.
@ TODO: Allow activity and workspace as CHECKIN request-URL.
@ TODO: Allow CHECKOUT to apply to a versionable resource (like
LOCK).
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@ TODO: Describe how BIND can mount the root versioned collection
of a repository at an arbitrary URL, even at another authority.
@ TODO: Mention that the If-Modified-Since header cannot be used to
reliably cache versioned resource information since the
modification date can decrease.
@ Does Versioning have to be a header, or can it be the body of the
OPTIONS response?
@ Couldn't MKRESOURCE be handled just by allowing PROPPATCH to be
applied to a null resource?
@ Do members of a versioned collection revision have to be
versioned resources?
@ Should we define which properties are optional, and which can
have an empty string as a value?
@ Should there be a report to enumerate the repositories and
workspaces ?
@ Is there already an DAV property like DAV:author?
@ Should dead properties like DAV:author and DAV:comment be in
another document
METHOD Template
Preconditions:
{What are the expected preconditions of the method, and what
happens if these preconditions are violated. For example, a common
precondition is the resource identified by the Request-URI must
exist.}
Request Marshalling:
{How are the arguments for the method marshalled. For WebDAV, this
includes stating which headers must be present, and which XML
elements are present in the request body.}
Postconditions:
{It states the postconditions of the method, giving easily
validated postconditions. Some examples of postconditions are
effects on the state of the resource, including body and
properties, and effects on the resource's parent collection.
Postconditions will often vary depending on the type of the
resource executing the method.}
Response Marshalling:
{It states how the results of the method are marshalled, including
the response for success, and the responses which are generated
when the postconditions cannot be achieved.}
Effect on Existing Resource Types:
Clemm, Kaler [Page 47]
INTERNET-DRAFT WebDAV Versioning May10, 2000
{How does this method work on all the different types of resources
defined so far (collections, redirect references, ordinary
resources, etc.)}
Clemm, Kaler [Page 48]
