.. _dci:subject:

Subject (MA, 0-n)
============

``datacite:subject``

Subject, keyword, classification code, or key phrase describing the resource.

*Allowed values, other constraints:*

* In general, choose the most significant and unique words for keywords, avoiding those too general to describe a particular resource.
* Usage of a controlled thesaurus or classification is highly recommended.
* For keywords/keyphrases that are not controlled by a vocabulary or thesaurus:

  * Either encode multiple terms with a semi-colon separating each keyword/keyphrase, or repeat the element for each term.
  * There are no requirements regarding the capitalization of keywords though internal (within archive) consistency is recommended.

* Where terms are taken from a standard classification schema or controlled vocabulary:

  * Encode each term using the additional attributes of the subject property. Encode the complete subject descriptor according to the relevant scheme. 
  * Use the capitalisation and punctuation used in the original scheme.
  * It is recommended to use an URI especially when codified schemes are used like DDC or UDC. Service providers can recognise encoding schemas more easily when the schema is “URI-fied” by an authority namespace.
  * If no specific classification scheme is used we recommend the Dewey Decimal Classification (DDC). More information about the DDC and the DDC Summaries can be found at https://www.oclc.org/en/dewey/resources.html . Please note that OCLC owns all copyright rights in the Dewey Decimal Classification system. Dewey, Dewey Decimal Classification, DDC, OCLC and WebDewey are registered trademarks of OCLC.

Property subject (MA, 0-n)
--------------------------

Use subject name or keyword as value.

.. _dci:subject_subjectScheme:

Attribute subjectScheme (O, 0-1)
~~~~~~~~~~~~~~~~

The name of the subject scheme or classification code or authority if one is used.

*Exemplary values:*

* ``DDC`` - |DDC|
* ``STW`` - |STW|
* ``AGROVOC`` - |AGROVOC|

.. _dci:subject_schemeUri:

Attribute schemeURI (O, 0-1)
~~~~~~~~~~~~~~~~

The URI of the subject identifier scheme.

*Exemplary values:*

* http://id.loc.gov/authorities/subjects
* http://zbw.eu/stw
* http://aims.fao.org/standards/agrovoc

Attribute valueURI (O, 0-1)
~~~~~~~~~~~~~~~~

The URI of the subject term.

Attribute xml:lang (R, 0-1)
~~~~~~~~~~~~~~~~

The language of the subject synonym.

*Recommended value lists:*

* IETF BCP 47 - |IETF BCP 47|
* ISO 639-x - |ISO 639-x|

Examples
-------

.. code-block:: xml
   :linenos:

   <datacite:subjects>
    <datacite:subject>Earth sciences and geology</datacite:subject>
    <datacite:subject subjectScheme="DDC" schemeURI="http://dewey.info/" valueURI="">
    551 Geology, hydrology, meteorology
    </datacite:subject>
   </datacite:subjects>

.. _DataCite MetadataKernel: http://schema.datacite.org/meta/kernel-4.3/

Context
-------

**Do Not Confuse With**

* :ref:`dci:description` (Use ``description`` for an abstract)
* :ref:`dci:title` (Use ``title`` for the name of the resource)
* :ref:`dci:resourceType` (Use ``resourceType`` for the type)

**DataCite v4.3 Differentiation**

* `xml:lang`_ is *recommenced* in OpenAIRE instead of *optional* in DataCite.

**OpenAIRE Data Guidelines v Differentiation**

* `xml:lang`_ is newly added.
* `valueUri`_ is newly added.