Link Relation Types for Simple Version Navigation between Web ResourcesIBM3565 Harbor BlvdCosta MesaCalifornia92626USAalbertcbrown@us.ibm.comIBM20 Maguire RoadLexingtonMA02421USAgeoffrey.clemm@us.ibm.comgreenbytes GmbHHafenweg 16MuensterNW48155Germanyjulian.reschke@greenbytes.dehttp://greenbytes.de/tech/webdav/
This specification defines a set of link relation types that may be
used on Web resources for navigation between a resource and
other resources related to version control, such as past versions
and working copies.
This specification defines a set of link relation types that may be
used on Web resources that exist in a system that supports versioning
to navigate among the different resources available, such as past versions
and working copies.
These link relations are used in the AtomPub () bindings
of the "Content Management Interoperability Services" (CMIS). See
for
further information.
Versioned Resource
When a resource is put under version control, it becomes a "versioned
resource". Many servers protect versioned resources
from modifications by considering them "checked in", and by requiring a
"checkout" operation before modification, and a "checkin" operation to
get back to the "checked-in" state. Other servers allow modification,
in which case the checkout/checkin operation may happen implicitly.
Version History
A "version history" resource is a resource that contains all the
versions of a particular versioned resource.
Predecessor, Successor
When a versioned resource is checked out and then subsequently checked
in, the version that was checked out becomes a "predecessor" of the
version created by the checkin. A client can specify multiple
predecessors for a new version if the new version is logically a merge of
those predecessors. The inverse of the predecessor relation is the
"successor" relation. Therefore, if X is a predecessor of Y, then Y is a
successor of X.
Working Copy
A "working copy" is a resource at a server-defined URL that can be
used to create a new version of a versioned resource.
Checkout
A "checkout" is an operation on a versioned resource that creates a
working copy, or changes the versioned resource to be a working copy as
well ("in-place versioning").
Checkin
A "checkin" is an operation on a working copy that creates a new version of
its corresponding versioned resource.
Note: the operations for putting a resource under version
control and for checking in and checking out depend on the protocol in
use and are beyond the scope of this document; see ,
, and for examples.
The following link relations are defined.
When included on a versioned resource, this link points to a resource
containing the version history for this resource.
When included on a versioned resource, this link points to a resource
containing the latest (e.g., current) version.
The latest version is defined by the system. For linear versioning
systems, this is probably the latest version by timestamp. For systems
that support branching, there will be multiple latest versions, one for
each branch in the version history.
Some systems may allow more than one of these link relations.
When included on a versioned resource, this link points to a working copy
for this resource.
Some systems may allow more than one of these link relations.
When included on a working copy, this link points to the versioned resource
from which this working copy was obtained.
When included on a versioned resource, this link points to a resource
containing the predecessor version in the version history.
Some systems may allow more than one of these link relations in the case of
multiple branches merging.
When included on a versioned resource, this link points to a resource
containing the successor version in the version history.
Some systems may allow more than one of these link relations in order to
support branching.
The link relations below have been registered by IANA per :
version-history
See .
Undefined; this relation can be used for background processing or to provide
extended functionality without displaying its value.
See .
latest-version
See .
Undefined; this relation can be used for background processing or to provide
extended functionality without displaying its value.
See .
working-copy
See .
Undefined; this relation can be used for background processing or to provide
extended functionality without displaying its value.
See .
working-copy-of
See .
Undefined; this relation can be used for background processing or to provide
extended functionality without displaying its value.
See .
predecessor-version
See .
Undefined; this relation can be used for background processing or to provide
extended functionality without displaying its value.
See .
successor-version
See .
Undefined; this relation can be used for background processing or to provide
extended functionality without displaying its value.
See .
Automated agents should take care when these relations
cross administrative domains (e.g., the URI has a different
authority than the current document).
Such agents should also take care to detect circular references.
Care should be applied when versioned resources are subject to differing
access policies. In this case, exposing links may leak information even if
the linked resource itself is properly secured. In particular, the syntax of
the link target could expose sensitive information (see
for a similar consideration
in WebDAV Versioning).
Note that this applies to exposing link metadata in general,
not only to links related to versioning.
Thanks to the members of Content Management Interoperability Services (CMIS)
Technical Committee (TC) at OASIS for the initial proposal, and to Jan
Algermissen for feedback during IETF review.
The Atom Syndication FormatVersioning Extensions to WebDAV (Web Distributed
Authoring and Versioning)Rational Software (IBM)IBMMicrosoftU.C. Santa CruzThe Atom Publishing ProtocolGooglejoe@bitworking.orgNewBay Softwarebill@dehora.netContent Repository API for Java(tm) Technology SpecificationDay SoftwareDay SoftwareDay SoftwareWeb Linkingmnot@mnot.nethttp://www.mnot.net/Work in ProgressContent Management Interoperability Services (CMIS) Version 1.0IBMMicrosoftOracleOpenTextLatest version available at
The link relations defined in correspond to
various properties used in WebDAV Versioning
and JCR :
version-history
WebDAV: the resource identified by the DAV:version-history property
(, Sections and ).
JCR: the node identified by jcr:versionHistory
property () for
versionable nodes, the parent folder for version nodes.
latest-version
WebDAV: for version-controlled resources, DAV:checked-in () or
DAV:checked-out (), depending
on checkin state. For version resources, a successor version that itself does
not have any successors.
JCR: the version node identified by the jcr:baseVersion property ()
for versionable nodes; for version nodes, a successor version that itself does
not have any successors.
working-copy
WebDAV: for version-controlled resources that are checked-out in place: the
resource itself. For version resources: each resource identified by a member
of the DAV:checkout-set property (see ).
JCR: for checked-out versionable nodes: the node itself.
working-copy-of
WebDAV: the resource identified by the DAV:checked-out
property (see ).
JCR: for checked-out versionable nodes: the node identified by the
jcr:baseVersion property ().
predecessor-version
WebDAV: each resource identified by a member of DAV:predecessor-set (, Sections and ).
JCR: each node identified by a member of jcr:predecessors ().
successor-version
WebDAV: each resource identified by a member of DAV:successor-set ().
JCR: each node identified by a member of jcr:successors ().
The "Web Linking" specification ()
generalizes Atom link relations, and also reintroduces the HTTP "Link"
header as a way to expose link relations in HTTP responses. This will make
it possible to expose version links independently from a specific vocabulary,
be it the Atom Feed Format () or WebDAV properties
().
For instance, a response to a VERSION-CONTROL request () could
expose a newly created version-history and checked-in version as link relations:
>> Request:
VERSION-CONTROL /docs/test.txt HTTP/1.1
Host: example.net
>> Response:
HTTP/1.1 204 No Content
Link: </system/v/84345634/1>; rel=latest-version;
anchor=</docs/test.txt>
Link: </system/vh/84345634>; rel=version-history;
anchor=</docs/test.txt>
(Note that in this case, the anchor parameter is used, as the
response to a VERSION-CONTROL request is not a representation of the resource
at the Request-URI.)
A subsequent HEAD request on that resource could expose the version-history
and latest-version relations as well:
>> Request:
HEAD /docs/test.txt HTTP/1.1
Host: example.net
>> Response:
HTTP/1.1 200 OK
Content-Type: text/plain; charset=UTF-8
Content-Length: 12345
Link: </system/v/84345634/1>; rel=latest-version
Link: </system/vh/84345634>; rel=version-history
After creating more versions, following the latest-version would then expose
predecessors of a version:
>> Request:
HEAD /system/v/84345634/3 HTTP/1.1
Host: example.net
>> Response:
HTTP/1.1 200 OK
Content-Type: text/plain; charset=UTF-8
Content-Length: 12323
Link: </system/v/84345634/2>; rel=predecessor-version