.. include:: /includes.rst.txt

.. comments - headings

   # with overline, for parts
   * with overline, for chapters
   = for sections
   - for subsections
   ^ for subsubsections
   " for paragraphs

.. index:: pair: Taxonomies; SKOS-XL

.. _skos_xl_target:

SKOS-XL Taxonomies
^^^^^^^^^^^^^^^^^^

SKOS-XL (SKOS eXtension for Labels) is a part of the W3C SKOS standard that lets you treat labels as resources in their own right, with their own metadata.
This may be useful for adding provenance data or information for text mining tools about how to use specific labels.
TopBraid EDG lets you use SKOS-XL to add any metadata you like to alternative and hidden labels.
Starting with release 6.3, EDG also lets you add metadata directly to links between a concept and its textual labels as detailed in :ref:`enabling_reification` .
This may serve as an alternative to SKOS-XL – an alternative that supports capture of label metadata without the added complexity of managing labels as independent resources.

To activate the SKOS-XL support for a particular taxonomy, select Settings > Includes and check SKOS XL SHACL Shapes to include SKOS-XL.
Then, when you edit concepts in that taxonomy, the edit forms will let you add existing label resources as the values of alternative and hidden labels.
Once a label’s data has been entered, it will appear like any other relationship property value on the relevant form: as a hypertext link.
You will be able create new labels using “Create New” as part of the editing concept information.
Or, alternatively, you can create and work with label resources independently from concepts.
To do so, switch to the Search panel (or Search layout) and select Label from the asset type navigator.

.. note::

 * SKOS-XL SHACL Shapes only provide skosXL:altLabel and skosXL:hiddenLabel relationships so that you can create separate label resources for them.

 * A concept still needs to have a textual label.
   This means that even with SKOS-XL, TopBraid EDG will continue to use skos:prefLabel as a direct label of a concept.

 * EDG uses resource’s textual label (either skos:prefLabel or rdfs:label) as a display name consistently across all the UI.
   Further, TopBraid EDG creates text indexes of concepts (and other resources) to facilitate auto-complete and search.
   The indexing process uses resource’s label.

SKOS-XL defines only one property for the Label class – literal form.
As previously mentioned, EDG uses either skos:prefLabel or rdfs:label as resource names.
There is a special “hard coded exception” from this rule for the SKOS-XL Label resources.
Even-though the create dialog for them says “label”, the value entered as a label is stored in the skosXL:literalForm property.
EDG will understand that for Label resources this property is used as their name.
To associate a new property with a SKOS-XL label use the same Ontology customization capabilities as you would use to create new properties for concepts.

Transform SKOS-XL
*****************

On the Transform tab of Taxonomies you will find an option to convert SKOS-XL labels to reified values.
This feature will convert any instances of ``skosxl:Label`` to values of their corresponding *direct* SKOS properties:

* ``skosxl:prefLabel`` is converted to ``skos:prefLabel``

* ``skosxl:altLabel`` is converted to ``skos:altLabel``

* ``skosxl:hiddenLabel`` is converted to ``skos:hiddenLabel``

If the ``skosxl:Label`` has other properties than ``skosxl:literalForm`` and ``rdf:type`` then these values will be converted into reified statements.
For example, if your ``skosxl:Label`` instances have values for ``ex:isAbbreviation`` and ``skosxl:prefLabel`` was used to point to the label, then there will be a reified triple attached to the ``skos:prefLabel`` statement to store these additional values.
The ontology should define suitable node shapes that define the properties such as ``ex:isAbbreviation`` for display and editing purposes, and attach them to the property shapes of properties such as ``skos:prefLabel`` using ``dash:reifiableBy``

Optionally, the original URIs of the ``skosxl:Label`` instances will be stored as reified triples and the property ``dash:uri`` which can then be used to restore the original ``skosxl:Label`` instances as part of an exporter.