Linked Data Fragments Server - Memento

This module adds support for the Memento Protocol to the Linked Data Fragments server. If your Linked Data source evolve over time and has multiple versions, it makes access and query across the various versions straightforward. To enable the Memento Protocol, follow the guide below.

This package is a Linked Data Fragments Server module.

Memento basics

Any data source can be configured as a Memento resource, meaning it represents a prior version of an existing data source. This is done by adding a mementos entry to your config file that introduces a new memento time gate path, identified by timegatePath. This time gate can contain several version, each pointing to a certain datasource using the mementoDatasource key. The version time range is identified using the versionStart and versionEnd timestamps. Each timestamp must be in ISO 8601 format.

For example, the datasources urn:ldf-server:myDbpedia2015 and urn:ldf-server:myDbpedia2014 are mementos of DBpedia valid in 2014 and 2015:

{
  "mementos": [
    {
      "timegatePath": "dbpedia",
      "versions": [
        {
          "mementoDatasource": "urn:ldf-server:myDbpedia2015",
          "start": "2014-09-14T11:59:59Z",
          "end": "2015-04-15T00:00:00Z",
          "originalBaseURL": "http://fragments.mementodepot.org/dbpedia_201510"
        },
        {
          "mementoDatasource": "urn:ldf-server:myDbpedia2014",
          "start": "2013-06-15T11:59:59Z",
          "end": "2014-09-15T00:00:00Z"
        }
      ]
    }
  ]
}

In case a version is hosted externally, you can specify the version's originalBaseURL to reconstruct its URL.

Example: DBpedia TPF archive

The Memento DBpedia LDF Server supports about 10 versions of DBpedia starting from 2007. A Memento Client like Memento for Chrome can be used to navigate the versions in a browser. The command line utility, cUrl, can also be used to see Memento in action. The following example queries the Memento LDF TimeGate to retrieve a Memento of the English DBpedia page around 15 March 2015.

$ curl -IL -H "Accept-Datetime: Wed, 15 Apr 2015 00:00:00 GMT" http://dbpedia.mementodepot.org/timegate/http://dbpedia.org/page/English

HTTP/1.1 302 Found
Date: Tue, 15 Mar 2016 21:07:08 GMT
Location: http://dbpedia.mementodepot.org/memento/20150415000000/http://dbpedia.org/page/English
Vary: accept-datetime
Link: <http://dbpedia.org/page/English>; rel="original",<http://dbpedia.mementodepot.org/timemap/link/http://dbpedia.org/page/English>; rel="timemap"; type="application/link-format",<http://dbpedia.mementodepot.org/memento/20150415000000/http://dbpedia.org/page/English>; rel="memento"; datetime="Wed, 15 Apr 2015 00:00:00 GMT"

HTTP/1.1 200 OK
Date: Tue, 15 Mar 2016 21:07:08 GMT
Content-Type: text/html
Link: <http://dbpedia.org/page/English>; rel="original", <http://dbpedia.mementodepot.org/memento/20150415000000/http://dbpedia.org/page/English>; rel="memento"; datetime="Wed, 15 Apr 2015 00:00:00 GMT", <http://dbpedia.mementodepot.org/timegate/http://dbpedia.org/page/English>; rel="timegate", <http://dbpedia.mementodepot.org/timemap/link/http://dbpedia.org/page/English>; rel="timemap"
Memento-Datetime: Wed, 15 Apr 2015 00:00:00 GMT

Usage in @ldf/server

This package exposes the following config entries:

• TimegateController: A TimegateController responds to time gate requests. This is enabled by default in @ldf/server. Should be used as @type value.
• MementoControllerExtension: A MementoControllerExtension extends Quad Pattern Fragments responses with Memento headers. This is enabled by default in @ldf/server. Should be used as @type value.
• MementoQpfHtmlView: A MementoHtmlViewExtension extends the Quad Pattern Fragments HTML view with Memento details. This is enabled by default in @ldf/server. Should be used as @type value.
• timegateBaseUrl: The base URL for all Memento time gates. Should be used as key in a Server config.
• mementos: One or more Memento configurations. Should be used as key in a Server config.
• timegatePath: URL path for a Memento within a time gate. Should be used as key in memento value.
• versions: Version entries for a given Memento. Should be used as key in memento value.
• mementoDatasource: The datasource corresponding to a given version. Should be used as key in memento version value.
• versionStart: The start datetime of a given version. Should be used as key in memento version value.
• versionEnd: The end datetime of a given version. Should be used as key in memento version value.
• mementoBaseURL: An optional external memento base URL to override. Should be used as key in memento version value.

@ldf/server and @ldf/preset-qpf provide default instantiations of TimegateController, MementoControllerExtension and MementoQpfHtmlView, which means that you don't have to define them in your config file yourself. The only thing you still need to do is defining the time gate and its mementos, as shown in the example below.

Example:

{
  "@context": "https://linkedsoftwaredependencies.org/bundles/npm/@ldf/server/^3.0.0/components/context.jsonld",
  "@id": "urn:ldf-server:my",
  "import": "preset-qpf:config-defaults.json",

  "datasources": [
    {
      "@id": "urn:ldf-server:myDatasourceVersion1",
      "@type": "SparqlDatasource",
      "datasourceTitle": "My SPARQL source",
      "description": "My datasource with a SPARQL-endpoint back-end",
      "datasourcePath": "mysparql",
      "sparqlEndpoint": "https://dbpedia.org/sparql"
    },
    {
      "@id": "urn:ldf-server:myDatasourceVersion2",
      "@type": "TurtleDatasource",
      "datasourceTitle": "My Turtle file",
      "description": "My dataset with a Turtle back-end",
      "datasourcePath": "myttl",
      "file": "path/to/file.ttl"
    }
  ],

  "timegateBaseUrl": "/timegate/",
  "mementos": [
    {
      "timegatePath": "mydatasource",
      "versions": [
        {
          "mementoDatasource": "urn:ldf-server:myDatasourceVersion1",
          "versionStart": "2014-09-14T11:59:59Z",
          "versionEnd": "2015-04-15T00:00:00Z"
        },
        {
          "mementoDatasource": "urn:ldf-server:myDatasourceVersion2",
          "versionStart": "2015-06-15T11:59:59Z",
          "versionEnd": "2016-09-15T00:00:00Z",
          "mementoBaseURL": "http://fragments.mementodepot.org/dbpedia_201510"
        }
      ]
    }
  ]
}

Usage in other packages

When this module is used in a package other than @ldf/server, then the JSON-LD context https://linkedsoftwaredependencies.org/contexts/@ldf/feature-memento.jsonld must be imported.

For example:

{
  "@context": [
    "https://linkedsoftwaredependencies.org/bundles/npm/@ldf/core/^3.0.0/components/context.jsonld",
    "https://linkedsoftwaredependencies.org/bundles/npm/@ldf/preset-qpf/^3.0.0/components/context.jsonld",
    "https://linkedsoftwaredependencies.org/bundles/npm/@ldf/feature-qpf/^3.0.0/components/context.jsonld",
    "https://linkedsoftwaredependencies.org/bundles/npm/@ldf/feature-memento/^3.0.0/components/context.jsonld",
  ],
  "@id": "urn:ldf-server:my",

  "controllers": [
    {
      "@id": "urn:ldf-server:myTimegateController",
      "@type": "TimegateController"
    },
    {
      "@id": "urn:ldf-server:myQuadPatternFragmentsController", // This should refer to your existing QuadPatternFragmentsController
      "@type": "QuadPatternFragmentsController",
      "qpfControllerExtension": {
        "@id": "urn:ldf-server:myMementoControllerExtension",
        "@type": "MementoControllerExtension"
      }
    }
  ],

  "views": [
    {
      "@id": "urn:ldf-server:myQpfHtmlView", // This should refer to your existing QpfHtmlView
      "@type": "QpfHtmlView",
      "viewExtension": {
        "@id": "urn:ldf-server:myMementoQpfHtmlView",
        "@type": "MementoQpfHtmlView"
      }
    }
  ]

  // Same as above...
}

License

The Linked Data Fragments server is written by Ruben Verborgh, Miel Vander Sande, Ruben Taelman and colleagues.

This code is copyrighted by Ghent University – imec and released under the MIT license.