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GeezerVison is showing datatracker.ietf.org — RFC 7089: HTTP Framework for Time-Based Access to Resource States -- Memento Independent Submission H. Van de Sompel
Request for Comments: 7089 Los Alamos National Laboratory
Category: Informational M. Nelson
ISSN: 2070-1721 Old Dominion University
R. Sanderson
Los Alamos National Laboratory
December 2013
RFC 7089 HTTP Memento December 2013 Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Table of Contents 1. Introduction ....................................................4 1.1. Terminology ................................................4 1.2. Notational Conventions .....................................4 1.3. Purpose ....................................................5 2. HTTP Headers, Link Relation Types ...............................7 2.1. HTTP Headers ...............................................7 2.1.1. Accept-Datetime and Memento-Datetime ................7 2.1.2. Vary ................................................8 2.1.3. Link ................................................8 2.2. Link Relation Types ........................................9 2.2.1. Link Relation Type "original" .......................9 2.2.2. Link Relation Type "timegate" .......................9 2.2.3. Link Relation Type "timemap" ........................9 2.2.4. Link Relation Type "memento" .......................10 3. Overview of the Memento Framework ..............................11 3.1. Datetime Negotiation ......................................11 3.2. TimeMaps ..................................................13 4. Datetime Negotiation: HTTP Interactions ........................14 4.1. Pattern 1 - The Original Resource Acts as Its Own TimeGate ..................................................15 4.1.1. Pattern 1.1 - URI-R=URI-G; 302-Style Negotiation; Distinct URI-M for Mementos ..........16 4.1.2. Pattern 1.2 - URI-R=URI-G; 200-Style Negotiation; Distinct URI-M for Mementos ...........18 4.1.3. Pattern 1.3 - URI-R=URI-G; 200-Style Negotiation; No Distinct URI-M for Mementos ........19 4.2. Pattern 2 - A Remote Resource Acts as a TimeGate for the Original Resource .................................20 4.2.1. Pattern 2.1 - URI-R<>URI-G; 302-Style Negotiation; Distinct URI-M for Mementos ...........22 4.2.2. Pattern 2.2 - URI-R<>URI-G; 200-Style Negotiation; Distinct URI-M for Mementos ...........24 4.2.3. Pattern 2.3 - URI-R<>URI-G; 200-Style Negotiation; No Distinct URI-M for Mementos ........25 Van de Sompel, et al. Informational [Page 2] RFC 7089 HTTP Memento December 2013 4.3. Pattern 3 - The Original Resource is a Fixed Resource .....26 4.4. Pattern 4 - Mementos without a TimeGate ...................27 4.5. Special Cases .............................................29 4.5.1. Original Resource Provides No "timegate" Link ......29 4.5.2. Server Exists but Original Resource No Longer Does ........................................29 4.5.3. Issues with Accept-Datetime ........................30 4.5.4. Memento of a 3XX Response ..........................30 4.5.5. Memento of Responses with 4XX or 5XX HTTP Status Codes .......................................32 4.5.6. Sticky "Memento-Datetime" and "original" Link for Mementos ..................................33 4.5.7. Intermediate Resources .............................34 4.5.8. Resources Excluded from Datetime Negotiation .......35 5. TimeMaps: Content and Serialization ............................36 5.1. Special Cases .............................................38 5.1.1. Index and Paging TimeMaps ..........................38 5.1.2. Mementos for TimeMaps ..............................39 6. IANA Considerations ............................................40 6.1. HTTP Headers ..............................................40 6.2. Link Relation Types .......................................40 7. Security Considerations ........................................41 8. Acknowledgements ...............................................42 9. References .....................................................42 9.1. Normative References ......................................42 9.2. Informative References ....................................42 Appendix A. Use of Headers and Relation Types per Pattern .........43 Van de Sompel, et al. Informational [Page 3] RFC 7089 HTTP Memento December 2013 RFC 7089 HTTP Memento December 2013 RFC 7089 HTTP Memento December 2013 In the abstract, the Memento framework introduces a mechanism to access versions of Web resources that: o Is fully distributed in the sense that resource versions may reside on multiple servers, and that any such server is likely only aware of the versions it holds; o Uses the global notion of datetime as a resource version indicator and access key; o Leverages the following primitives of [W3C.REC-aww-20041215]: resource, resource state, representation, content negotiation, and link. The core components of Memento's mechanism to access resource versions are: 1. The abstract notion of the state of an Original Resource (URI-R) as it existed at datetime T. Note the relationship with the ability to identify the state of a resource at datetime T by means of a URI as intended by the proposed Dated URI scheme [DATED-URI]. 2. A "bridge" from the present to the past, consisting of: o The existence of a TimeGate (URI-G), which is aware of (at least part of the) version history of the Original Resource (URI-R); o The ability to negotiate in the datetime dimension with that TimeGate (URI-G), as a means to access the state that the Original Resource (URI-R) had at datetime T. 3. A "bridge" from the past to the present, consisting of an appropriately typed link from a Memento (URI-M), which encapsulates the state the Original Resource (URI-R) had at datetime T, to the Original Resource (URI-R). 4. The existence of a TimeMap (URI-T) from which a list of all Mementos that encapsulate a prior state of the Original Resource (URI-R) can be obtained. This document is concerned with specifying an instantiation of these abstractions for resources that are identified by HTTP(S) URIs. Van de Sompel, et al. Informational [Page 6] RFC 7089 HTTP Memento December 2013 RFC 7089 HTTP Memento December 2013 the BNF in Figure 1. This BNF is derived from the HTTP-date construction of the BNF for Full Dates provided in [RFC2616]. The datetime is case sensitive with names for days and months exactly as shown in the wkday and month construction rules of the BNF, respectively. The datetime MUST be represented in Greenwich Mean Time (GMT). accept-dt-value = rfc1123-date rfc1123-date = wkday "," SP date1 SP time SP "GMT" date1 = 2DIGIT SP month SP 4DIGIT ; day month year (e.g., 20 Mar 1957) time = 2DIGIT ":" 2DIGIT ":" 2DIGIT ; 00:00:00 - 23:59:59 (e.g., 14:33:22) wkday = "Mon" | "Tue" | "Wed" | "Thu" | "Fri" | "Sat" | "Sun" month = "Jan" | "Feb" | "Mar" | "Apr" | "May" | "Jun" | "Jul" | "Aug" | "Sep" | "Oct" | "Nov" | "Dec" Figure 1: BNF for the Datetime Format RFC 7089 HTTP Memento December 2013 RFC 7089 HTTP Memento December 2013 be a datetime expressed according to the rfc1123-date construction rule of the BNF in Figure 1, and it MUST be represented in Greenwich Mean Time (GMT). Use in HTTP "Link" headers: If there is a TimeMap associated with an Original Resource, a TimeGate, or a Memento that is preferred for use, then responses to HTTP HEAD/GET requests issued against these latter resources MUST include a link with a "timemap" Relation Type in their HTTP "Link" header. Multiple such links, each with a distinct Target IRI, MAY be expressed as a means to point to different TimeMaps or to different serializations of the same TimeMap. In all cases, use of the "from" and "until" attributes is OPTIONAL. RFC 7089 HTTP Memento December 2013 RFC 7089 HTTP Memento December 2013 Step 1: The user agent that wants to access a prior state of the Original Resource issues an HTTP HEAD/GET against URI-R that has an "Accept-Datetime" HTTP header with a value of the datetime of the desired state. Step 2: The response from URI-R includes an HTTP "Link" header with a Relation Type of "timegate" pointing at a TimeGate (URI-G) for the Original Resource. Step 3: The user agent starts the datetime negotiation process with the TimeGate by issuing an HTTP GET request against URI-G that has an "Accept-Datetime" HTTP header with a value of the datetime of the desired prior state of the Original Resource. Step 4: The response from URI-G includes a "Location" header pointing at a Memento (URI-M) for the Original Resource. In addition, the response contains an HTTP "Link" header with a Relation Type of "original" pointing at the Original Resource (URI-R), and an HTTP "Link" header with a Relation Type of "timemap" pointing at a TimeMap (URI-T). Step 5: The user agent issues an HTTP GET request against URI-M. Step 6: The response from URI-M includes a "Memento-Datetime" HTTP header with a value of the archival datetime of the Memento. It also contains an HTTP "Link" header with a Relation Type of "original" pointing at the Original Resource (URI-R), with a Relation Type of "timegate" pointing at a TimeGate (URI-G) for the Original Resource, and with a Relation Type of "timemap" pointing at a TimeMap (URI-T) for the Original Resource. The state that is expressed by the response is the state the Original Resource had at the archival datetime expressed in the "Memento-Datetime" header. In order to respond to a datetime negotiation request, the server uses an internal algorithm to select the Memento that best meets the user agent's datetime preference. The exact nature of the selection algorithm is at the server's discretion but is intended to be consistent, for example, always selecting the Memento that is nearest in time relative to the requested datetime, always selecting the Memento that is nearest in the past relative to the requested datetime, etc. Due to the sparseness of Mementos in most systems, the value of the "Memento-Datetime" header returned by a server may differ (significantly) from the value conveyed by the user agent in "Accept- Datetime". Van de Sompel, et al. Informational [Page 12] RFC 7089 HTTP Memento December 2013 Although a Memento encapsulates a prior state of an Original Resource, the entity-body returned in response to an HTTP GET request issued against a Memento may very well not be byte-to-byte the same as an entity-body that was previously returned by that Original Resource. Various reasons exist why there are significant chances these would be different yet do convey substantially the same information. These include format migrations as part of a digital preservation strategy, URI-rewriting as applied by some Web archives, and the addition of banners as a means to brand Web archives. When negotiating in the datetime dimension, the regular content negotiation dimensions (media type, character encoding, language, and compression) remain available. It is the TimeGate server's responsibility to honor (or not) such content negotiation, and in doing so it MUST always first select a Memento that meets the user agent's datetime preference, and then consider honoring regular content negotiation for it. As a result of this approach, the returned Memento will not necessarily meet the user agent's regular content negotiation preferences. Therefore, it is RECOMMENDED that the server provides "memento" links in the HTTP "Link" header pointing at Mementos that do meet the user agent's regular content negotiation requests and that have a value for the "Memento-Datetime" header in the temporal vicinity of the user agent's preferred datetime value. A user agent that engages in datetime negotiation with a resource typically starts by issuing an HTTP HEAD, not GET, request with an "Accept-Datetime" header in order to determine how to proceed. This strategy is related to the existence of various server implementation patterns as will become clear in Section 4. Details about the HTTP interactions involved in datetime negotiation are provided in Section 4. RFC 7089 HTTP Memento December 2013 1: UA --- HTTP HEAD/GET ------------------------------------> URI-R 2: UA <-- HTTP 200; Link: URI-G ----------------------------- URI-R 3: UA --- HTTP HEAD/GET ------------------------------------> URI-G 4: UA <-- HTTP 302; Location: URI-M; Vary; Link: URI-R,URI-T ------------------------------------------> URI-G 5: UA --- HTTP GET URI-T -----------------------------------> URI-T 6: UA <-- HTTP 200 ------------------------------------------ URI-T Figure 3: A Request/Response Chain to Obtain a TimeMap Step 1: The user agent that wants to access a TimeMap for the Original Resource issues an HTTP HEAD/GET against URI-R. This can be done with or without an "Accept-Datetime" HTTP header. Step 2: Irrespective of the use of an "Accept-Datetime" HTTP header in Step 1, the response from URI-R includes an HTTP "Link" header with a Relation Type of "timegate" pointing at a TimeGate (URI-G) for the Original Resource. Step 3: The user agent issues an HTTP GET request against URI-G. This can be done with or without an "Accept-Datetime" HTTP header. Step 4: Irrespective of the use of an "Accept-Datetime" HTTP header in Step 1, the response contains an HTTP "Link" header with a Relation Type of "timemap" pointing at a TimeMap (URI-T). Step 5: The user agent issues an HTTP GET request against URI-T. Step 6: The response from URI-T has an entity-body that lists all Mementos for the Original Resource known to the responding server, as well as their archival datetimes. Details about the content and serialization of TimeMaps are provided in Section 5. RFC 7089 HTTP Memento December 2013 o Pattern 3 (Section 4.3) - The Original Resource is a Fixed Resource o Pattern 4 (Section 4.4) - Mementos without a TimeGate Details of the HTTP interactions for common cases for each of those patterns are provided in Sections 4.1 through 4.4. Appendix A summarizes the use of the "Vary", "Memento-Datetime", and "Link" headers in responses from Original Resources, TimeGates, and Mementos for the various patterns. Special cases are described in Section 4.5. Note that in the following sections, the HTTP status code of the responses with an entity-body is shown as "200 OK", but a series of "206 Partial Content" responses could be substituted. Figure 4 shows a user agent that attempts to datetime negotiate with the Original Resource http://a.example.org/ by including an "Accept- Datetime" header in its HTTP HEAD request. This initiating request is the same for Pattern 1 (Section 4.1) through Pattern 3 (Section 4.3). HEAD / HTTP/1.1 Host: a.example.org Accept-Datetime: Tue, 20 Mar 2001 20:35:00 GMT Connection: close Figure 4: User Agent Attempts Datetime Negotiation with Original Resource RFC 7089 HTTP Memento December 2013 +-------------------+------------+----------+---------+-------------+ | Pattern | Original | TimeGate | Memento | Negotiation | | | Resource | | | Style | +-------------------+------------+----------+---------+-------------+ | Pattern 1.1 | URI-R | URI-R | URI-M | 302 | | (Section 4.1.1) | | | | | | Pattern 1.2 | URI-R | URI-R | URI-M | 200 | | (Section 4.1.2) | | | | | | Pattern 1.3 | URI-R | URI-R | URI-R | 200 | | (Section 4.1.3) | | | | | +-------------------+------------+----------+---------+-------------+ Table 1: Pattern 1 RFC 7089 HTTP Memento December 2013 HTTP/1.1 302 Found Date: Thu, 21 Jan 2010 00:06:50 GMT Server: Apache Vary: accept-datetime Location: http://a.example.org/?version=20010320133610 Link: <http://a.example.org/>; rel="original timegate" Content-Length: 0 Content-Type: text/plain; charset=UTF-8 Connection: close Figure 5: Response from URI-R=URI-G for Pattern 1.1 In a subsequent request, shown in Figure 6, the user agent can obtain the selected Memento by issuing an HTTP GET request against the URI-M that was provided in the "Location" header. The inclusion of the "Accept-Datetime" header in this request is not needed but will typically occur as the user agent is in datetime negotiation mode. GET /?version=20010320133610 HTTP/1.1 Host: a.example.org Accept-Datetime: Tue, 20 Mar 2001 20:35:00 GMT Connection: close Figure 6: User Agent Requests Selected Memento The response has a "200 OK" HTTP status code, and the entity-body of the response contains the representation of the selected Memento. The use of Memento response headers and links in the response from URI-M is as follows: o A "Vary" header that includes an "accept-datetime" value MUST NOT be provided. o The response MUST include a "Memento-Datetime" header. Its value expresses the archival datetime of the Memento. o The "Link" header MUST be provided, and it MUST contain at least a link with the "original" Relation Type that has the URI-R of the Original Resource as Target IRI. The provision of other links is encouraged and is subject to the considerations described in Section 2.2. The server's response to the request of Figure 6 is shown in Figure 7. Note the provision of the required "original", and the recommended "timegate" and "timemap" links. The former two point to Van de Sompel, et al. Informational [Page 17] RFC 7089 HTTP Memento December 2013 the Original Resource, which acts as its own TimeGate. The latter has "from" and "until" attributes to indicate the temporal interval covered by Mementos listed in the linked TimeMap. HTTP/1.1 200 OK Date: Thu, 21 Jan 2010 00:06:51 GMT Server: Apache-Coyote/1.1 Memento-Datetime: Tue, 20 Mar 2001 13:36:10 GMT Link: <http://a.example.org/>; rel="original timegate", <http://a.example.org/?version=all&style=timemap> ; rel="timemap"; type="application/link-format" ; from="Tue, 15 Sep 2000 11:28:26 GMT" ; until="Wed, 20 Jan 2010 09:34:33 GMT" Content-Length: 23364 Content-Type: text/html;charset=utf-8 Connection: close Figure 7: Response from URI-M for Pattern 1.1 RFC 7089 HTTP Memento December 2013 HTTP/1.1 200 OK Date: Thu, 21 Jan 2010 00:06:50 GMT Server: Apache Vary: accept-datetime Content-Location: http://a.example.org/?version=20010320133610 Memento-Datetime: Tue, 20 Mar 2001 13:36:10 GMT Link: <http://a.example.org/>; rel="original timegate", <http://a.example.org/?version=20000915112826> ; rel="memento first"; datetime="Tue, 15 Sep 2000 11:28:26 GMT", <http://a.example.org/?version=20100120093433> ; rel="memento last"; datetime="Wed, 20 Jan 2010 09:34:33 GMT", <http://a.example.org/?version=all&style=timemap> ; rel="timemap"; type="application/link-format" Content-Length: 23364 Content-Type: text/html;charset=utf-8 Connection: close Figure 8: Response from URI-R=URI-G for Pattern 1.2 In a subsequent request, which is the same as Figure 4 but with HTTP GET instead of HEAD, the user agent can obtain the representation of the selected Memento. It will be provided as the entity-body of a response that has the same Memento headers as in Figure 8. RFC 7089 HTTP Memento December 2013 The server's response to the request of Figure 4 is shown in Figure 9. The recommended "timemap" and "timegate" links are included in addition to the mandatory "original" link. HTTP/1.1 200 OK Date: Thu, 21 Jan 2010 00:06:50 GMT Server: Apache Vary: accept-datetime Memento-Datetime: Tue, 20 Mar 2001 13:36:10 GMT Link: <http://a.example.org/>; rel="original timegate", <http://a.example.org/?version=all&style=timemap> ; rel="timemap"; type="application/link-format" Content-Length: 23364 Content-Type: text/html;charset=utf-8 Connection: close Figure 9: Response from URI-R=URI-G for Pattern 1.3 In a subsequent request, which is the same as Figure 4 but with HTTP GET instead of HEAD, the user agent can obtain the representation of the selected Memento. It will be provided as the entity-body of a response that has the same Memento headers as in Figure 9. RFC 7089 HTTP Memento December 2013 +-------------------+------------+----------+---------+-------------+ | Pattern | Original | TimeGate | Memento | Negotiation | | | Resource | | | Style | +-------------------+------------+----------+---------+-------------+ | Pattern 2.1 | URI-R | URI-G | URI-M | 302 | | (Section 4.2.1) | | | | | | Pattern 2.2 | URI-R | URI-G | URI-M | 200 | | (Section 4.2.2) | | | | | | Pattern 2.3 | URI-R | URI-G | URI-G | 200 | | (Section 4.2.3) | | | | | +-------------------+------------+----------+---------+-------------+ Table 2: Pattern 2 The response by the Original Resource to the request shown in Figure 4 is the same for all three cases. The use of headers and links in the response from URI-R is as follows: o A "Vary" header that includes an "accept-datetime" value MUST NOT be provided. o The response MUST NOT contain a "Memento-Datetime" header. o The "Link" header SHOULD be provided. It MUST NOT include a link with an "original" Relation Type. If a preferred TimeGate is associated with the Original Resource, then it MUST include a link with a "timegate" Relation Type that has the URI-G of the TimeGate as Target IRI. If a preferred TimeMap is associated with the Original Resource, then it SHOULD include a link with a "timemap" Relation Type that has the URI-T of the TimeGate as Target IRI. Multiple "timegate" and "timemap" links can be provided to accommodate situations in which the server is aware of multiple TimeGates or TimeMaps for the Original Resource. Figure 10 shows such a response. Note the absence of an "original" link as the responding resource is neither a TimeGate nor a Memento. HTTP/1.1 200 OK Date: Thu, 21 Jan 2010 00:02:12 GMT Server: Apache Link: <http://arxiv.example.net/timegate/http://a.example.org/> ; rel="timegate" Content-Length: 255 Connection: close Content-Type: text/html; charset=iso-8859-1 Figure 10: Response from URI-R<>URI-G for Pattern 2 Van de Sompel, et al. Informational [Page 21] RFC 7089 HTTP Memento December 2013 Once a user agent has obtained the URI-G of a remote TimeGate for the Original Resource, it can engage in datetime negotiation with that TimeGate. Figure 11 shows the request issued against the TimeGate, whereas Sections 4.2.1 through 4.2.3 detail the responses for various TimeGate implementation patterns. HEAD /timegate/http://a.example.org/ HTTP/1.1 Host: arxiv.example.net Accept-Datetime: Tue, 20 Mar 2001 20:35:00 GMT Connection: close Figure 11: User Agent Engages in Datetime Negotiation with Remote TimeGate RFC 7089 HTTP Memento December 2013 HTTP/1.1 302 Found Date: Thu, 21 Jan 2010 00:02:14 GMT Server: Apache Vary: accept-datetime Location: http://arxiv.example.net/web/20010321203610/http://a.example.org/ Link: <http://a.example.org/>; rel="original", <http://arxiv.example.net/timemap/http://a.example.org/> ; rel="timemap"; type="application/link-format" ; from="Tue, 15 Sep 2000 11:28:26 GMT" ; until="Wed, 20 Jan 2010 09:34:33 GMT" Content-Length: 0 Content-Type: text/plain; charset=UTF-8 Connection: close Figure 12: Response from URI-G<>URI-R for Pattern 2.1 In a subsequent HTTP GET request, shown in Figure 13, the user agent can obtain the selected Memento by issuing an HTTP GET request against the URI-M that was provided in the "Location" header. The inclusion of the "Accept-Datetime" header in this request is not needed but will typically occur as the user agent is in datetime negotiation mode. GET /web/20010321203610/http://a.example.org/ HTTP/1.1 Host: arxiv.example.net/ Accept-Datetime: Tue, 20 Mar 2001 20:35:00 GMT Connection: close Figure 13: User Agent Requests Selected Memento The response has a "200 OK" HTTP status code. The use of Memento response headers and links in the response from URI-M is as follows: o A "Vary" header that includes an "accept-datetime" value MUST NOT be provided. o The response MUST include a "Memento-Datetime" header. Its value expresses the archival datetime of the Memento. o The "Link" header MUST be provided, and it MUST contain at least a link with the "original" Relation Type that has the URI-R of the Original Resource as Target IRI. The provision of other links is encouraged and is subject to the considerations described in Section 2.2. Van de Sompel, et al. Informational [Page 23] RFC 7089 HTTP Memento December 2013 The server's response to the request of Figure 13 is shown in Figure 14. Note the provision of the recommended "timegate" and "timemap" links. HTTP/1.1 200 OK Date: Thu, 21 Jan 2010 00:02:15 GMT Server: Apache-Coyote/1.1 Memento-Datetime: Wed, 21 Mar 2001 20:36:10 GMT Link: <http://a.example.org/>; rel="original", <http://arxiv.example.net/timemap/http://a.example.org/> ; rel="timemap"; type="application/link-format", <http://arxiv.example.net/timegate/http://a.example.org/> ; rel="timegate" Content-Length: 25532 Content-Type: text/html;charset=utf-8 Connection: close Figure 14: Response from URI-M for Pattern 2.1 RFC 7089 HTTP Memento December 2013 HTTP/1.1 200 OK Date: Thu, 21 Jan 2010 00:09:40 GMT Server: Apache-Coyote/1.1 Vary: accept-datetime Content-Location: http://arxiv.example.net/web/20010321203610/http://a.example.org/ Memento-Datetime: Wed, 21 Mar 2001 20:36:10 GMT Link: <http://a.example.org/>; rel="original", <http://arxiv.example.net/timemap/http://a.example.org/> ; rel="timemap"; type="application/link-format", <http://arxiv.example.net/timegate/http://a.example.org/> ; rel="timegate" Content-Length: 25532 Content-Type: text/html;charset=utf-8 Connection: close Figure 15: Response from URI-G<>URI-R for Pattern 2.2 In a subsequent request, which is the same as Figure 11 but with HTTP GET instead of HEAD, the user agent can obtain the representation of the selected Memento. It will be provided as the entity-body of a response that has the same Memento headers as Figure 15. RFC 7089 HTTP Memento December 2013 The server's response to the request of Figure 11 is shown in Figure 16. HTTP/1.1 200 OK Date: Thu, 21 Jan 2010 00:09:40 GMT Server: Apache-Coyote/1.1 Vary: accept-datetime Memento-Datetime: Wed, 21 Mar 2001 20:36:10 GMT Link: <http://a.example.org/>; rel="original", <http://arxiv.example.net/timemap/http://a.example.org/> ; rel="timemap"; type="application/link-format", <http://arxiv.example.net/timegate/http://a.example.org/> ; rel="timegate" Content-Length: 25532 Content-Type: text/html;charset=utf-8 Connection: close Figure 16: Response from URI-G<>URI-R for Pattern 2.3 In a subsequent request, which is the same as Figure 11 but with HTTP GET instead of HEAD, the user agent can obtain the representation of the selected Memento. It will be provided as the entity-body of a response that has the same Memento headers as Figure 16. RFC 7089 HTTP Memento December 2013 Servers that host such resources can support the Memento framework by treating the stable resource (FixedResource as per [W3C.gen-ont-20090420]) as a Memento. The use of Memento response headers and links in responses from such a stable resource is as follows: o A "Vary" header that includes an "accept-datetime" value MUST NOT be provided. o The response MUST include a "Memento-Datetime" header. Its value expresses the datetime at which the resource became stable. Providing this value includes a promise that the resource has not changed since this datetime and will not change anymore beyond it. o The "Link" header MUST be provided and MUST have a link with the "original" Relation Type that has the URI-R of the stable resource itself as Target IRI. Figure 17 shows a response to an HTTP HEAD request for the resource with URI-R http://a.example.org/ that has been stable since March 20, 2009. HTTP/1.1 200 OK Date: Thu, 21 Jan 2010 00:09:40 GMT Server: Apache-Coyote/1.1 Memento-Datetime: Fri, 20 Mar 2009 11:00:00 GMT Link: <http://a.example.org/>; rel="original" Content-Length: 875 Content-Type: text/html;charset=utf-8 Connection: close Figure 17: Response from URI-R=URI-M for Pattern 3 RFC 7089 HTTP Memento December 2013 +----------+----------------+----------+---------+------------------+ | Pattern | Original | TimeGate | Memento | Negotiation | | | Resource | | | Style | +----------+----------------+----------+---------+------------------+ | Pattern | URI-R | - | URI-M | - | | 4 | | | | | +----------+----------------+----------+---------+------------------+ Table 4: Pattern 4 Servers that host such Mementos without TimeGates can still support the Memento framework by providing the appropriate Memento headers and links. Their use is as follows for a response from URI-M: o A "Vary" header that includes an "accept-datetime" value MUST NOT be provided. o The response MUST include a "Memento-Datetime" header. Its value expresses the archival datetime of the Memento. o The "Link" header MUST be provided, and it MUST have a link with the "original" Relation Type that has the URI-R of the associated Original Resource as Target IRI. The provision of other links is encouraged and is subject to the considerations described in Section 2.2. Figure 18 shows a response to an HTTP HEAD request for the Memento with URI-M http://arxiv.example.net/web/20010321203610/http://a.example.org/. Note the use of links: three links have the URI-M of the Memento as Target IRI and have respective Relation Types "memento", "first", and "last". This combination indicates that this is the only Memento for the Original Resource with Target IRI provided by the "original" link (http://a.example.org/) of which the server is aware. Note also that such a response does not imply that there is no server whatsoever that exposes a TimeGate; it merely means that the responding server neither provides nor is aware of the location of a TimeGate. Van de Sompel, et al. Informational [Page 28] RFC 7089 HTTP Memento December 2013 HTTP/1.1 200 OK Date: Thu, 21 Jan 2010 00:09:40 GMT Server: Apache-Coyote/1.1 Memento-Datetime: Wed, 21 Mar 2001 20:36:10 GMT Link: <http://a.example.org/>; rel="original", <http://arxiv.example.net/web/20010321203610/http://a.example.org/> ; rel="first last memento" ; datetime="Wed, 21 Mar 2001 20:36:10 GMT" Content-Length: 25532 Content-Type: text/html;charset=utf-8 Connection: close Figure 18: Response from URI-M<>URI-R for Pattern 4 RFC 7089 HTTP Memento December 2013 HTTP/1.1 404 Not Found Date: Thu, 21 Jan 2010 00:02:12 GMT Server: Apache Link: <http://arxiv.example.net/timegate/http://a.example.org/pic> ; rel="timegate" Content-Length: 255 Content-Type: text/html; charset=iso-8909-1 Connection: close Figure 19: Response from an Original Resource That No Longer Exists RFC 7089 HTTP Memento December 2013 The user agent's handling of an HTTP response with a 3XX status code is not affected by the presence of a "Memento-Datetime" header. The user agent MUST behave in the same manner as it does with HTTP responses with a 3XX status code that do not have a "Memento- Datetime" header. However, the user agent MUST be aware that the URI that was selected from the "Location" header of an HTTP response with a 3XX status code might not be that of a Memento but rather of an Original Resource. In the latter case, it SHOULD proceed by looking for a Memento of the selected Original Resource. For example, Figure 20 shows the response to an HTTP GET request for http://a.example.org issued on April 11, 2008. This response is archived as a Memento of http://a.example.org that has as URI-M http://arxiv.example.net/web/20080411000650/http://a.example.org. The response to an HTTP GET on this URI-M is shown in Figure 21. It is a replay of the original response with "Memento-Datetime" and "Link" headers added, to allow a user agent to understand the response is a Memento. In Figure 21, the value of the "Location" header is the same as in the original response; it identifies an Original Resource. The user agent proceeds with finding a Memento for this Original Resource. Web archives sometimes overwrite the value that was originally provided in the "Location" header in order to point at a Memento they hold of the resource to which the redirect originally led. This is shown in Figure 22. In this case, the user agent may decide it found an appropriate Memento. HTTP/1.1 301 Moved Permanently Date: Fri, 11 Apr 2008 00:06:50 GMT Server: Apache Location: http://b.example.org Content-Length: 0 Content-Type: text/plain; charset=UTF-8 Connection: close Figure 20: Response Is a Redirect Van de Sompel, et al. Informational [Page 31] RFC 7089 HTTP Memento December 2013 HTTP/1.1 301 Moved Permanently Date: Thu, 21 Jan 2010 00:09:40 GMT Server: Apache-Coyote/1.1 Memento-Datetime: Fri, 11 Apr 2008 00:06:50 GMT Location: http://b.example.org Link: <http://a.example.org>; rel="original", <http://arxiv.example.net/timemap/http://a.example.org> ; rel="timemap"; type="application/link-format", <http://arxiv.example.net/timegate/http://a.example.org> ; rel="timegate" Content-Length: 0 Content-Type: text/plain; charset=UTF-8 Connection: close Figure 21: Response is a Memento of a Redirect; Leads to an Original Resource HTTP/1.1 301 Moved Permanently Date: Thu, 21 Jan 2010 00:09:40 GMT Server: Apache-Coyote/1.1 Memento-Datetime: Fri, 11 Apr 2008 00:06:50 GMT Location: http://arxiv.example.net/web/20080411000655/http://b.example.org Link: <http://a.example.org>; rel="original", <http://arxiv.example.net/timemap/http://a.example.org> ; rel="timemap"; type="application/link-format", <http://arxiv.example.net/timegate/http://a.example.org> ; rel="timegate" Content-Length: 0 Content-Type: text/plain; charset=UTF-8 Connection: close Figure 22: Response is a Memento of a Redirect; Leads to a Memento RFC 7089 HTTP Memento December 2013 is a replay of the original response with "Memento-Datetime" and "Link" headers added, to allow a user agent to understand the response is a Memento. HTTP/1.1 404 Not Found Date: Fri, 11 Apr 2008 00:06:50 GMT Server: Apache Content-Length: 255 Content-Type: text/plain; charset=UTF-8 Connection: close Figure 23: Response Is a 404 HTTP/1.1 404 Not Found Date: Thu, 21 Jan 2010 00:09:40 GMT Server: Apache-Coyote/1.1 Memento-Datetime: Fri, 11 Apr 2008 00:06:50 GMT Link: <http://a.example.org>; rel="original", <http://arxiv.example.net/timemap/http://a.example.org> ; rel="timemap"; type="application/link-format", <http://arxiv.example.net/timegate/http://a.example.org> ; rel="timegate" Content-Length: 255 Content-Type: text/plain; charset=UTF-8 Connection: close Figure 24: Response Is a Memento of a 404 RFC 7089 HTTP Memento December 2013 their original assignment, and the server MUST NOT change the value of the "Memento-Datetime" header nor the Target IRI of the "original" link. o Applications that mirror Mementos at a different URI MUST retain them and MUST NOT change them unless mirroring involves a meaningful state change. This allows, among others, duplicating a Web archive at a new location while preserving the value of the "Memento-Datetime" header and the link with the "original" Relation Type for the archived resources. For example, when mirroring, the "Last-Modified" header will be updated to reflect the time of mirroring at the new URI, whereas the value for "Memento-Datetime" will be maintained. RFC 7089 HTTP Memento December 2013 HTTP/1.1 302 Found Date: Thu, 21 Jan 2010 00:06:50 GMT Server: Apache Location: http://arxiv.example.net/new-timegate/http://a.example.org/ Link: <http://a.example.org>; rel="original" Content-Length: 0 Content-Type: text/plain; charset=UTF-8 Connection: close Figure 25: Redirecting Resource Redirects to a TimeGate RFC 7089 HTTP Memento December 2013 RFC 7089 HTTP Memento December 2013 GET /timemap/http://a.example.org/ HTTP/1.1 Host: arxiv.example.net Accept: application/link-format;q=1.0 Connection: close Figure 27: Request for a TimeMap If the TimeMap requested by the user agent exists, the server's response has a "200 OK" HTTP status code and the list of Mementos is provided in the entity-body of the response. Such a response is shown in Figure 28. HTTP/1.1 200 OK Date: Thu, 21 Jan 2010 00:06:50 GMT Server: Apache Content-Length: 4883 Content-Type: application/link-format Connection: close <http://a.example.org>;rel="original", <http://arxiv.example.net/timemap/http://a.example.org> ; rel="self";type="application/link-format" ; from="Tue, 20 Jun 2000 18:02:59 GMT" ; until="Wed, 09 Apr 2008 20:30:51 GMT", <http://arxiv.example.net/timegate/http://a.example.org> ; rel="timegate", <http://arxiv.example.net/web/20000620180259/http://a.example.org> ; rel="first memento";datetime="Tue, 20 Jun 2000 18:02:59 GMT" ; license="http://creativecommons.org/publicdomain/zero/1.0/", <http://arxiv.example.net/web/20091027204954/http://a.example.org> ; rel="last memento";datetime="Tue, 27 Oct 2009 20:49:54 GMT" ; license="http://creativecommons.org/publicdomain/zero/1.0/", <http://arxiv.example.net/web/20000621011731/http://a.example.org> ; rel="memento";datetime="Wed, 21 Jun 2000 01:17:31 GMT" ; license="http://creativecommons.org/publicdomain/zero/1.0/", <http://arxiv.example.net/web/20000621044156/http://a.example.org> ; rel="memento";datetime="Wed, 21 Jun 2000 04:41:56 GMT" ; license="http://creativecommons.org/publicdomain/zero/1.0/", ... Figure 28: Response from a TimeMap Van de Sompel, et al. Informational [Page 37] RFC 7089 HTTP Memento December 2013 RFC 7089 HTTP Memento December 2013 <http://a.example.org>;rel="original", <http://arxiv.example.net/timegate/http://a.example.org> ; rel="timegate", <http://arxiv.example.net/timemap/1/http://a.example.org> ; rel="self";type="application/link-format" ; from="Tue, 20 Jun 2000 18:02:59 GMT" ; until="Wed, 09 Apr 2008 20:30:51 GMT", <http://arxiv.example.net/timemap/2/http://a.example.org> ; rel="timemap";type="application/link-format" ; from="Thu, 10 Apr 2008 20:30:51 GMT" ; until="Tue, 27 Oct 2009 20:49:54 GMT", <http://arxiv.example.net/timemap/3/http://a.example.org> ; rel="timemap";type="application/link-format" ; from="Thu, 29 Oct 2009 20:30:51 GMT" ; until="Fri, 31 Aug 2012 12:22:34 GMT" <http://arxiv.example.net/web/20000620180259/http://a.example.org> ; rel="memento";datetime="Tue, 20 Jun 2000 18:02:59 GMT", <http://arxiv.example.net/web/20000621011731/http://a.example.org> ; rel="memento";datetime="Wed, 21 Jun 2000 01:17:31 GMT", <http://arxiv.example.net/web/20000621044156/http://a.example.org> ; rel="memento";datetime="Wed, 21 Jun 2000 04:41:56 GMT", ... Figure 30: Paging TimeMap RFC 7089 HTTP Memento December 2013 HTTP/1.1 200 OK Date: Thu, 21 Jan 2010 00:06:50 GMT Server: Apache Link: <http://arxiv.example.net/timemap/http://a.example.org> ; anchor="http://a.example.org"; rel="timemap" ; type="application/link-format" Content-Length: 0 Content-Type: application/link-format; charset=UTF-8 Connection: close Figure 31: TimeMap Links to the Original Resource It Is about RFC 7089 HTTP Memento December 2013 o Relation Name: timegate o Description: The Target IRI points to a TimeGate for an Original Resource. o Reference: this document o Notes: A TimeGate for an Original Resource is a resource that is capable of datetime negotiation to support access to prior states of the Original Resource. o Relation Name: timemap o Description: The Target IRI points to a TimeMap for an Original Resource. o Reference: this document o Notes: A TimeMap for an Original Resource is a resource from which a list of URIs of Mementos of the Original Resource is available. o Relation Name: memento o Description: The Target IRI points to a Memento, a fixed resource that will not change state anymore. o Reference: this document o Notes: A Memento for an Original Resource is a resource that encapsulates a prior state of the Original Resource. RFC 7089 HTTP Memento December 2013 RFC 7089 HTTP Memento December 2013 [W3C.REC-aww-20041215] Jacobs, I. and N. Walsh, "Architecture of the World Wide Web", December 2004, <http://www.w3.org/TR/webarch/>. [W3C.gen-ont-20090420] Berners-Lee, T., "Architecture of the World Wide Web", April 2009, <http://www.w3.org/2006/gen/ont>. Van de Sompel, et al. Informational [Page 43] RFC 7089 HTTP Memento December 2013 RFC 7089 HTTP Memento December 2013 +-----------------+-----------------+----------+----------+---------+ | Response Header | Pattern | Original | TimeGate | Memento | | | | Resource | | | +-----------------+-----------------+----------+----------+---------+ | Vary: | | | | | | Memento- | Pattern 1.1 | 0 | 0 | 1 | | Datetime | (Section 4.1.1) | | | | | | & | | | | | | Pattern 1.2 | | | | | | (Section 4.1.2) | | | | | | | | | | | | Pattern 1.3 | 1 | 1 | 1 | | | (Section 4.1.3) | | | | | | | | | | | | Pattern 2.1 | 0 | 0 | 1 | | | (Section 4.2.1) | | | | | | & | | | | | | Pattern 2.2 | | | | | | (Section 4.2.2) | | | | | | | | | | | | Pattern 2.3 | 0 | 1 | 1 | | | (Section 4.2.3) | | | | | | | | | | | | Pattern 3 | 1 | NA | 1 | | | (Section 4.3) | | | | | | | | | | | | Pattern 4 | 0 | NA | 1 | | | (Section 4.4) | | | | +-----------------+-----------------+----------+----------+---------+ (cont.) Van de Sompel, et al. Informational [Page 45] RFC 7089 HTTP Memento December 2013 +-----------------+-----------------+----------+----------+---------+ | Response Header | Pattern | Original | TimeGate | Memento | | | | Resource | | | +-----------------+-----------------+----------+----------+---------+ | Link: | | | | | | rel="original" | Pattern 1.1 | 0 | 1 | 1 | | | (Section 4.1.1) | | | | | | & | | | | | | Pattern 1.2 | | | | | | (Section 4.1.2) | | | | | | | | | | | | Pattern 1.3 | 1 | 1 | 1 | | | (Section 4.1.3) | | | | | | | | | | | | Pattern 2.1 | 0 | 1 | 1 | | | (Section 4.2.1) | | | | | | & | | | | | | Pattern 2.2 | | | | | | (Section 4.2.2) | | | | | | | | | | | | Pattern 2.3 | 0 | 1 | 1 | | | (Section 4.2.3) | | | | | | | | | | | | Pattern 3 | 1 | NA | 1 | | | (Section 4.3) | | | | | | | | | | | | Pattern 4 | 0 | NA | 1 | | | (Section 4.4) | | | | +-----------------+-----------------+----------+----------+---------+ (cont.) Van de Sompel, et al. Informational [Page 46] RFC 7089 HTTP Memento December 2013 +-----------------+-----------------+----------+----------+---------+ | Response Header | Pattern | Original | TimeGate | Memento | | | | Resource | | | +-----------------+-----------------+----------+----------+---------+ | Link: | | | | | | rel="timegate" | Pattern 1.1 | >=0 | >=0 | >=0 | | | (Section 4.1.1) | | | | | | & | | | | | | Pattern 1.2 | | | | | | (Section 4.1.2) | | | | | | | | | | | | Pattern 1.3 | >=0 | >=0 | >=0 | | | (Section 4.1.3) | | | | | | | | | | | | Pattern 2.1 | >=0 | 0 | >=0 | | | (Section 4.2.1) | | | | | | & | | | | | | Pattern 2.2 | | | | | | (Section 4.2.2) | | | | | | | | | | | | Pattern 2.3 | >=0 | >=0 | >=0 | | | (Section 4.2.3) | | | | | | | | | | | | Pattern 3 | NA | NA | NA | | | (Section 4.3) | | | | | | | | | | | | Pattern 4 | NA | NA | NA | | | (Section 4.4) | | | | +-----------------+-----------------+----------+----------+---------+ (cont.) Van de Sompel, et al. Informational [Page 47] RFC 7089 HTTP Memento December 2013 +-----------------+-----------------+----------+----------+---------+ | Response Header | Pattern | Original | TimeGate | Memento | | | | Resource | | | +-----------------+-----------------+----------+----------+---------+ | Link: | | | | | | rel="timemap" | Pattern 1.1 | >=0 | >=0 | >=0 | | | (Section 4.1.1) | | | | | | & | | | | | | Pattern 1.2 | | | | | | (Section 4.1.2) | | | | | | | | | | | | Pattern 1.3 | >=0 | >=0 | >=0 | | | (Section 4.1.3) | | | | | | | | | | | | Pattern 2.1 | >=0 | >=0 | >=0 | | | (Section 4.2.1) | | | | | | & | | | | | | Pattern 2.2 | | | | | | (Section 4.2.2) | | | | | | | | | | | | Pattern 2.3 | >=0 | >=0 | >=0 | | | (Section 4.2.3) | | | | | | | | | | | | Pattern 3 | >=0 | NA | >=0 | | | (Section 4.3) | | | | | | | | | | | | Pattern 4 | >=0 | NA | >=0 | | | (Section 4.4) | | | | | | | | | | +-----------------+-----------------+----------+----------+---------+ (cont.) Van de Sompel, et al. Informational [Page 48] RFC 7089 HTTP Memento December 2013 +-----------------+-----------------+----------+----------+---------+ | Response Header | Pattern | Original | TimeGate | Memento | | | | Resource | | | +-----------------+-----------------+----------+----------+---------+ | Link: | | | | | | rel="memento" | Pattern 1.1 | >=0 | >=0 | >=0 | | | (Section 4.1.1) | | | | | | & | | | | | | Pattern 1.2 | | | | | | (Section 4.1.2) | | | | | | | | | | | | Pattern 1.3 | >=0 | >=0 | >=0 | | | (Section 4.1.3) | | | | | | | | | | | | Pattern 2.1 | >=0 | >=0 | >=0 | | | (Section 4.2.1) | | | | | | & | | | | | | Pattern 2.2 | | | | | | (Section 4.2.2) | | | | | | | | | | | | Pattern 2.3 | >=0 | >=0 | >=0 | | | (Section 4.2.3) | | | | | | | | | | | | Pattern 3 | >=0 | NA | >=0 | | | (Section 4.3) | | | | | | | | | | | | Pattern 4 | >=0 | NA | >=0 | | | (Section 4.4) | | | | +-----------------+-----------------+----------+----------+---------+ Table 5: Memento Headers Van de Sompel, et al. Informational [Page 49] RFC 7089 HTTP Memento December 2013 Authors' Addresses Herbert Van de Sompel Los Alamos National Laboratory PO Box 1663 Los Alamos, New Mexico 87545 USA Phone: +1 505 667 1267 EMail: [email protected] URI: http://public.lanl.gov/herbertv/ Michael Nelson Old Dominion University Norfolk, Virginia 23529 USA Phone: +1 757 683 6393 EMail: [email protected] URI: http://www.cs.odu.edu/~mln/ Robert Sanderson Los Alamos National Laboratory PO Box 1663 Los Alamos, New Mexico 87545 USA Phone: +1 505 665 5804 EMail: [email protected] URI: http://public.lanl.gov/rsanderson/ Van de Sompel, et al. Informational [Page 50]
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