
.. _metadata-head:

Metadata
========

What is metadata?
-----------------

The word "metadata" means "data about data". Metadata articulates a context for
objects of interest -- "resources" such as MP3 files, library books, or
satellite images -- in the form of "resource descriptions". As a tradition,
resource description dates back to the earliest archives and library catalogs.
During the Web revolution of the mid-1990s, `Dublin Core <http://dublincore.org/metadata-basics/>`_
has emerged as one of the prominent metadata standards.

Why use metadata?
-----------------

Uploading a document to several servers can be very tricky, because the
document has to be saved in a place where it can be easily found with basic
searches in all storages (For instance: ERP5, XWiki and Mioga2 have their own
way to save documents and to get them). So we must use metadata for
*interoperability reasons*. Interoperability is the ability of diverse systems
and organizations to work together.

How to format metadata with jIO
-------------------------------

See below XML and its JSON equivalent:

+--------------------------------------------+---------------------------------------+
| XML                                        | JSON                                  |
+============================================+=======================================+
| .. code-block:: xml                        | .. code-block:: javascript            |
|                                            |                                       |
|   <dc:title>My Title</dc:title>            |   {"title": "My Title"}               |
+--------------------------------------------+---------------------------------------+
| .. code-block:: xml                        | .. code-block:: javascript            |
|                                            |                                       |
|   <dc:contributor>Me</dc:contributor>      |   {"contributor": ["Me", "And You"]}  |
|   <dc:contributor>And You</dc:contributor> |                                       |
+--------------------------------------------+---------------------------------------+
| .. code-block:: xml                        | .. code-block:: javascript            |
|                                            |                                       |
|    <dc:identifier scheme="DCTERMS.URI">    |   {"identifier": [                    |
|      http://my/resource                    |     {                                 |
|    </dc:identifier>                        |       "scheme": "DCTERMS.URI",        |
|    <dc:identifier>                         |       "content": "http://my/resource" |
|      Xaoe41PAPNIWz                         |     },                                |
|    </dc:identifier>                        |     "Xaoe41PAPNIWz"                   |
|                                            |   ]}                                  |
+--------------------------------------------+---------------------------------------+

List of metadata to use
-----------------------

Identification
^^^^^^^^^^^^^^

* **_id**

  A specific jIO metadata which helps the storage to find a document
  (can be a real path name, a dc:identifier, a uuid, ...). **String Only**

* **identifier**

  | ``{"identifier": "http://domain/jio_home_page"}``
  | ``{"identifier": "urn:ISBN:978-1-2345-6789-X"}``
  | ``{"identifier": [{"scheme": "DCTERMS.URI", "content": "http://domain/jio_home_page"}]}``

  An unambiguous reference to the resource within a given context. Recommended
  best practice is to identify the resource with a string or number
  conforming to a formal identification system. Examples of formal identification
  systems include the `Uniform Resource Identifier <http://en.wikipedia.org/wiki/URI>`_ (URI)
  (including the `Uniform Resource Locator <http://en.wikipedia.org/wiki/URL>`_ (URL)),
  the `Digital Object Identifier <http://en.wikipedia.org/wiki/Digital_object_identifier>`_ (DOI)
  and the `International Standard Book Number <http://en.wikipedia.org/wiki/Isbn>`_ (ISBN).

* **format**

  | ``{"format": ["text/html", "52 kB"]}``
  | ``{"format": ["image/jpeg", "100 x 100 pixels", "13.2 KiB"]}``

  The physical or digital manifestation of the resource. Typically, Format may
  include the media-type or dimensions of the resource. Examples of dimensions
  include size and duration. Format may be used to determine the software,
  hardware or other equipment needed to display or operate the resource.

* **date**

  | ``{"date": "2011-12-13T14:15:16Z"}``
  | ``{"date": {"scheme": "DCTERMS.W3CDTF", "content": "2011-12-13"}}``

  A date associated with an event in the life cycle of the resource. Typically,
  Date is associated with the creation or availability of the resource.
  Recommended best practice for encoding the date value is defined in a profile
  of ISO 8601 `Date and Time Formats, W3C Note <http://www.w3.org/TR/NOTE-datetime>`_
  and follows the YYYY-MM-DD format.

* **type**

  | ``{"type": "Text"}``
  | ``{"type": "Image"}``
  | ``{"type": "Dataset"}``

  The nature or genre of the content of the resource. Type includes terms describing
  general categories, functions, genres, or aggregation levels for content.
  Recommended best practice is to select a value from a controlled vocabulary.
  **This type is not a MIME Type!**


Intellectual property
^^^^^^^^^^^^^^^^^^^^^

* **creator**

  | ``{"creator": "Tristan Cavelier"}``
  | ``{"creator": ["Tristan Cavelier", "Sven Franck"]}``

  An entity primarily responsible for creating the content of the resource.
  Examples of a Creator include a person, an organization, or a service.
  Typically the name of the Creator should be used to indicate the entity.

* **publisher**

  | ``{"publisher": "Nexedi"}``

  The entity responsible for making the resource available. Examples of a
  Publisher include a person, an organization, or a service. Typically, the name
  of a Publisher should be used to indicate the entity.

* **contributor**

  | ``{"contributor": ["Full Name", "Full Name", ...]}``

  An entity responsible for making contributions to the content of the
  resource. Examples of a Contributor include a person, an organization or a
  service. Typically, the name of a Contributor should be used to indicate the
  entity.

* **rights**

  | ``{"rights": "Access limited to members"}``
  | ``{"rights": "https://www.j-io.org/documentation/jio-documentation/#copyright-and-license"}``

  Information about rights held in and over the resource. Typically a Rights
  element should contain a rights management statement for the resource, or
  reference a service providing such information. Rights information often
  encompasses Intellectual Property Rights (IPR), Copyright, and various Property
  Rights. If the rights element is absent, no assumptions can be made about the
  status of these and other rights with respect to the resource.


Content
^^^^^^^

* **title**

  | ``{"title": "jIO Home Page"}``

  The name given to the resource. Typically, a Title is a name by which the resource is formally known.

* **subject**

  | ``{"subject": "jIO"}``
  | ``{"subject": ["jIO", "basics"]}``

  The topic of the content of the resource. Typically, a Subject is
  expressed as keywords or key phrases or classification codes that describe the
  topic of the resource. Recommended best practice is to select a value from a
  controlled vocabulary or formal classification scheme.

* **description**

  | ``{"description": "Simple guide to show the basics of jIO"}``
  | ``{"description": {"lang": "fr", "content": "Ma description"}}``

  An account of the content of the resource. Description may include but is not
  limited to: an abstract, table of contents, reference to a graphical
  representation of content or a free-text account of the content.

* **language**

  | ``{"language": "en"}``

  The language of the intellectual content of the resource. Recommended best
  practice for the values of the Language element is defined by `RFC 3066 <http://www.ietf.org/rfc/rfc3066.txt>`_
  which, in conjunction with `ISO 639 <http://www.oasis-open.org/cover/iso639a.html>`_, defines two- and
  three-letter primary language tags with optional subtags. Examples include "en"
  or "eng" for English, "akk" for Akkadian, and "en-GB" for English used in the
  United Kingdom.

* **source**

  | ``{"source": ["Image taken from a drawing by Mr. Artist", "<phone number>"]}``

  A Reference to a resource from which the present resource is derived. The
  present resource may be derived from the Source resource in whole or part.
  Recommended best practice is to reference the resource by means of a string or
  number conforming to a formal identification system.

* **relation**

  | ``{"relation": "Resilience project"}``

  A reference to a related resource. Recommended best practice is to reference
  the resource by means of a string or number conforming to a formal
  identification system.

* **coverage**

  | ``{"coverage": "France"}``

  The extent or scope of the content of the resource. Coverage would typically
  include spatial location (a place name or geographic co-ordinates), temporal
  period (a period label, date, or date range) or jurisdiction (such as a named
  administrative entity). Recommended best practice is to select a value from a
  controlled vocabulary (for example, the `Getty Thesaurus of Geographic Names
  <http://www.getty.edu/research/tools/vocabulary/tgn/>`_. Where appropriate, named
  places or time periods should be used in preference to numeric identifiers such
  as sets of co-ordinates or date ranges.

* **category**

  | ``{"category": ["parent/26323", "resilience/javascript", "javascript/library/io"]}``

  The category the resource is associated with. The categories may look like
  navigational facets, they correspond to the properties of the resource which
  can be generated with metadata or some other information (see `faceted search <https://en.wikipedia.org/wiki/Faceted_search>`_).

* **product**

  | ``{"product": "..."}``

  For e-commerce use.

* **custom**

  | ``{custom1: value1, custom2: value2, ...}``



Examples
--------

Posting a webpage for jIO
^^^^^^^^^^^^^^^^^^^^^^^^^

.. code-block:: javascript

  jio.post({
    "identifier" : "http://domain/jio_home_page",
    "format"     : ["text/html", "52 kB"],
    "date"       : new Date(),
    "type"       : "Text",
    "creator"    : ["Nexedi", "Tristan Cavelier", "Sven Franck"],
    "title"      : "jIO Home Page",
    "subject"    : ["jIO", "basics"],
    "description": "Simple guide to show the basics of jIO",
    "category"   : ["resilience/jio", "webpage"],
    "language"   : "en"
  }); // send content as attachment


Posting jIO library
^^^^^^^^^^^^^^^^^^^

.. code-block:: javascript

  jio.post({
    "identifier" : "jio.js",
    "date"       : "2013-02-15",
    "format"     : "application/javascript",
    "type"       : "Software",
    "creator"    : ["Tristan Cavelier", "Sven Franck"],
    "publisher"  : "Nexedi",
    "rights"     :
      "https://www.j-io.org/documentation/" +
        "jio-documentation/#copyright-and-license",
    "title"      : "Javascript Input/Output",
    "subject"    : "jIO",
    "category"   : [
                       "resilience/javascript",
                       "javascript/library/io"
                   ]
    "description": "jIO is a client-side JavaScript library to " +
                   "manage documents across multiple storages."
  }); // send content as attachment


Posting a webpage for interoperability levels
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.. code-block:: javascript

  jio.post({
    "identifier" : "http://dublincore.org/documents/" +
                       "interoperability-levels/",
    "date"       : "2009-05-01",
    "format"     : "text/html",
    "type"       : "Text",
    "creator"    : [
                    "Mikael Nilsson",
                    "Thomas Baker",
                    "Pete Johnston"
                   ],
    "publisher"  : "Dublin Core Metadata Initiative",
    "title"      : "Interoperability Levels for Dublin Core Metadata",
    "description": "This document discusses the design choices " +
                   "involved in designing applications for " +
                   "different types of interoperability. [...]",
    "language"   : "en"
  }); // send content as attachment


Posting an image
^^^^^^^^^^^^^^^^

.. code-block:: javascript

  jio.post({
    "identifier" : "new_york_city_at_night",
    "format"     : ["image/jpeg", "7.2 MB", "8192 x 4096 pixels"],
    "date"       : "1999",
    "type"       : "Image",
    "creator"    : "Mr. Someone",
    "title"      : "New York City at Night",
    "subject"    : ["New York"],
    "description": "A photo of New York City taken just after midnight",
    "coverage"   : ["New York", "1996-1997"]
  }); // send content as attachment


Posting a book
^^^^^^^^^^^^^^

.. code-block:: javascript

  jio.post({
    "identifier" : {
                       "scheme": "DCTERMS.URI",
                       "content": "urn:ISBN:0385424728"
                   },
    "format"     : "application/pdf",
    "date"       : {
                       "scheme": "DCTERMS.W3CDTF",
                       "content": getW3CDate()
                   }, // see tools below
    "creator"    : "Original Author(s)",
    "publisher"  : "Me",
    "title"      : {"lang": "en", "content": "..."},
    "description": {"lang": "en", "Summary: ..."},
    "language"   : {
                       "scheme": "DCTERMS.RFC4646",
                       "content": "en-GB"
                   }
  }); // send content as attachment


Posting a video
^^^^^^^^^^^^^^^

.. code-block:: javascript

  jio.post({
    "identifier" : "my_video",
    "format"     : ["video/ogg", "130 MB", "1080p", "20 seconds"],
    "date"       : getW3CDate(), // see tools below
    "type"       : "Video",
    "creator"    : "Me",
    "title"      : "My life",
    "description": "A video about my life"
  }); // send content as attachment


Posting a job announcement
^^^^^^^^^^^^^^^^^^^^^^^^^^

.. code-block:: javascript

  jio.post({
    "format"     : "text/html",
    "date"       : "2013-02-14T14:44Z",
    "type"       : "Text",
    "creator"    : "James Douglas",
    "publisher"  : "Morgan Healey Ltd",
    "title"      : "E-Commerce Product Manager",
    "subject"    : "Job Announcement",
    "description": "Announcement for e-commerce product manager job",
    "language"   : "en-GB",
    "source"     : "James@morganhealey.com",
    "relation"   : ["Totaljobs"],
    "coverage"   : "London, South East",
    "job_type"   : "Permanent",
    "salary"     : "£45,000 per annum"
  }); // send content as attachment


Getting a list of document created by someone
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

With query:

.. code-block:: javascript

  jio.allDocs({"query": "creator: \"someone\""});


Getting all documents about jIO in the resilience project
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

With query:

.. code-block:: javascript

  jio.allDocs({
    "query": 'subject: "jIO" AND category: "resilience"'
  });


Tools
-----

Date functions
^^^^^^^^^^^^^^

.. code-block:: javascript

  // Get RFC1123 date format "Tue, 13 Dec 2011 13:15:16 GMT"
  new Date().toUTCString();

  // Get ISO8601 date format "2011-12-13T13:15:16.433Z"
  new Date().toISOString();

  /**
   * Tool to get the date in W3C date format.
   *
   *     "2011-12-13T14:15:16.433+01:00"
   *
   * @param  {Date} [date] The date to convert
   * @return {String} The date in W3C date format
   */
  function getW3CDate(date) {
    var d = date || new Date(), offset = - d.getTimezoneOffset();
    return (
      d.getFullYear() + "-" +
        (d.getMonth() + 1) + "-" +
        d.getDate() + "T" +
        d.getHours() + ":" +
        d.getMinutes() + ":" +
        d.getSeconds() + "." +
        d.getMilliseconds() +
        (offset < 0 ?
         "-" + parseInt(-offset / 60, 10) + ":" + (-offset % 60) :
         "+" + parseInt(offset / 60, 10) + ":" + (offset % 60))
    ).replace(/[0-9]+/g, function (found) {
      if (found.length < 2) {
        return '0' + found;
      }
      return found;
    });
  }


Sources
-------

* `Interoperability definition <https://en.wikipedia.org/wiki/Interoperability>`_
* `Faceted search <https://en.wikipedia.org/wiki/Faceted_search>`_
* `DublinCore <http://dublincore.org/>`_

  * `Interoperability levels <http://dublincore.org/documents/interoperability-levels/>`_
  * `Metadata elements <http://dublincore.org/documents/usageguide/elements.shtml>`_
  * http://www.chu-rouen.fr/documed/eahilsantander.html
  * http://openweb.eu.org/articles/dublin_core (French)

* `CouchDB <https://couchdb.apache.org/>`_
* `Resource Description Framework (RDF) <http://www.w3.org/RDF/>`_
* `Five Ws <https://en.wikipedia.org/wiki/Five_Ws>`_
* `Metadata <https://en.wikipedia.org/wiki/Metadata>`_
* MIME Types

  * https://en.wikipedia.org/wiki/Internet_media_type
  * https://www.iana.org/assignments/media-types
