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4.1 Versioned Resources

• When an LDPR is created with a rel="type" link in the Link header specifying type http://mementoweb.org/ns#OriginalResource to indicate versioning, it must be created as an LDPRv and a version container (LDPCv) must be created to contain Memento resources (LDPRm) capturing time-varying representations of the LDPRv. Patterns for version creation are described in 4.5 Implementation Patterns.
  
  • NB: Spec has changed: currently LDPRv is created using the type http://fedora.info/definitions/fcrepo#VersionedResource in the link header.

4.1.1 HTTP GET  (LDPRv)

• The Accept-Datetime header is used to request a past state, exactly as per [RFC7089] section 2.1.1. A successful response must be a 302 (Found) redirect to the appropriate LDPRm
• If no LDPRm is appropriate to the Accept-Datetime value, an implementation should return a 406 (Unacceptable).
  • curl -v -X GET http://localhost:8080/rest/test -H "Accept-Datetime: Thu, 31 May 2007 20:35:00 GMT" returns 200.
  • (db) Should a post to a non-LDPRv return 406?
• The response to a GET request on an LDPRv must include the following headers:
  • A rel="original timegate" link in the Link header referencing itself
  • A <http://mementoweb.org/ns#TimeGate>; rel="type" link in the Link header
  • A <http://mementoweb.org/ns#OriginalResource>; rel="type" link in the Link header
    • NB: Spec has changed: currently LDPRv is returning type http://fedora.info/definitions/fcrepo#VersionedResource
  • At least one rel="timemap" link in the Link header referencing an associated LDPCv
  • A Vary: Accept-Datetime header, exactly as per [RFC7089] section 2.1.2.

4.1.2 HTTP PUT (Danny Bernstein)

• An implementation must support PUT, as is the case for any LDPR.

4.2 Version Resources (LDPRm)

• An LDPRm may be deleted;
• however, it must not be modified once created.
  

4.2.1 HTTP GET §

• An implementation must support GET, as is the case for any LDPR.
• The headers for GET requests and responses on this resource must conform to [RFC7089] section 2.1. Particularly it should be noted that the relevant TimeGate for an LDPRm is the original versioned LDPRv.
• In addition, any response to a GET request must include a <http://mementoweb.org/ns#Memento>; rel="type" link in the Link header.

4.2.2 HTTP OPTIONS §

• An implementation must support OPTIONS.
• A response to an OPTIONS request must include Allow: GET, HEAD, OPTIONS as per [LDP].
• An implementation may include Allow: DELETE if clients can remove a version from the version history, as noted in 3.8 HTTP DELETE.

4.2.3 HTTP POST 

• An implementation must not support POST for LDPRms.

4.2.4 HTTP PUT 

• An implementation must not support PUT for LDPRms.

4.2.5 HTTP PATCH 

• An implementation must not support PATCH for LDPRms.

4.2.6 HTTP DELETE 

• An implementation may support DELETE for LDPRms. If DELETE is supported, the server is responsible for all behaviors implied by the LDP-containment of the LDPRm.

4.3 Version Containers (LDPCv) 

• An implementation must indicate TimeMap in the same way it indicates the container interaction model of the resource via HTTP headers.
• An implementation must not allow the creation of an LDPCv that is LDP-contained by its associated LDPRv.

4.3.1 HTTP GET 

• An implementation must support GET, as is the case for any LDPR. Any response to a GET request must include a <http://mementoweb.org/ns#TimeMap>; rel="type" link in the Link header.
• An LDPCv must respond to GET Accept: application/link-format as indicated in [RFC7089] section 5 and specified in [RFC6690] section 7.3.
• An implementation must include the Allow header as outlined in 4.3.2 HTTP OPTIONS.
• If an LDPCv supports POST, then it must include the Accept-Post header described in 4.3.3 HTTP POST.
• If an LDPCv supports PATCH, then it must include the Accept-Patch header.

4.3.2 HTTP OPTIONS 

• An implementation must Allow: GET, HEAD, OPTIONS as per [LDP].
• An implementation may Allow: DELETE if the versioning behavior is removable by deleting the LDPCv. See 4.3.4HTTP DELETE for requirements on DELETE if supported.
• An implementation may Allow: PATCH if the LDPCv has mutable properties. See 3.7.1 Containment Triples for requirements on PATCH if supported.
  • NB: it does not allow PATCH
• An implementation may Allow: POST if versions can be explicitly minted by a client. See 4.3.3 HTTP POST for requirements on POST if supported.
• Currently PUT is allowed. The spec doesn't explicitly ban it, but perhaps it should?

4.3.3 HTTP POST 

• Although an LDPCv is both a TimeMap and an LDPC, it may disallow POST requests.
• If an LDPCv supports POST, a POST that does not contain a Memento-Datetime header should be understood to create a new LDPRm contained by the LDPCv, reflecting the state of the LDPRv at the time of the POST. Any request body must be ignored.
• If an LDPCv supports POST, a POST with a Memento-Datetime header should be understood to create a new LDPRm contained by the LDPCv, with the state given in the request body and the datetime given in the Memento-Datetime request header.
• If an implementation does not support one or both of POST cases above, it must respond to such requests with a 4xx range status code and a link to an appropriate constraints document (see [LDP] 4.2.1.6).

4.3.4 HTTP DELETE 

• An implementation may support DELETE.
  • DELETE is advertised, but not currently implemented: do we plan to implement ?
• An implementation that does support DELETE should do so by both removing the LDPCv and removing the versioning interaction model from the original LDPRv.

4.4 Vary 

Non-normative note: When a POST to an LDPCv, or a PUT or PATCH to an LDPRv creates a new LDPRm, the response indicates this by using a Vary header as appropriate. When an LDPCv supports POST, and allows clients to specify a datetime for created URI-Ms, Vary-Post/Vary-Put: Memento-Datetime.

4.5 Implementation Patterns 

Non-normative note: This section describes the way the normative specification might be applied to implement discoverable versioning patterns. If an implementation of an LDPCv does not support POST to mint versions, that must be advertised via OPTIONS as described in 4.3.2 HTTP OPTIONS. This allows a client to perform an OPTIONS request on an LDPCv to determine if it can explicitly mint versions. If the LDPCv does not support POST, the client should assume some other mechanism is used to mint versions, for example, the implementation may automatically mint versions instead, but that is outside the requirements of this specification. This document specifies normatively only how LDPCvs and LDPRms can be discovered, and how they should act.

4.5.1 Server-Managed Version Creation §

Non-normative note: Upon PUT or PATCH to an LDPRv, a new LDPRm is created in an appropriate LDPCv. This LDPRm is the version of the original LDPRv that was just created.

4.5.2 Client-Managed Version Creation §

Non-normative note: An LDPRm for a particular LDPRv is created on POST to any LDPCv associated with that LDPRv. The new LDPRm is contained in the LDPCv to which the POST was made and features in that LDPCv-as-a-TimeMap. This pattern is very flexible and might be useful for migration from other systems into Fedora implementations. Responses from requests to the LDPRv include a rel="timemap" link in the Linkheader that references the same LDPCv as per [RFC7089] section 5.

4.5.3 Replacing Contents from Mementos §

Non-normative note: Using the ingest-by-reference mechanism, one can replace the contents of an LDPRvwith that of an LDPRm by providing it's URL as the URL parameter in a Content-Type: message/external-body header. For example, given an LDPRm with URL http://example.org/some/memento, the full header would be 
Content-Type: message/external-body; access-type=URL; expiration=1;
    URL="http://example.org/some/memento"