Using keywords from a thesaurus as queryables

18 September 2024 14:59:00 - by Paul van Genuchten

Using keywords from a thesaurus as queryables

A common convention in catalogues is the use of keywords from a dedicated thesaurus. The assignment of these keywords can then later be used to filter or query the catalogue by these terms. To achieve this use case in pycsw, some configuration needs to be tailored. This blog post indicates the changes needed for this scenario.

For this example we’ll use a keyword from the INSPIRE Themes thesaurus. We will define a new queryable inspiretheme, which will be populated with the relevant keyword (if present).

You can repeat these steps for any other thesaurus.

Extra database column

Extend the records table in the database with an extra field for the selected thesaurus. This is usually a manual operation on the database.

ALTER TABLE records
ADD inspiretheme VARCHAR(255);

Add parameter to pycsw

In pycsw/core/config.py the newly created database column can be registered to pycsw.

'pycsw:InspireTheme': 'inspiretheme',

Add column to mapping

etc/mappings.py links the pycsw parameter to the columnname in the table.

'pycsw:InspireTheme': 'inspiretheme',

Define parameter as queryable

Which of the parameters are queryable is defined in pycsw/core/repository.py.

'inspiretheme': self.dataset.inspiretheme,

Add parameter to record results?

Keywords are already published in records, so there is generally no need to extend the record with the new parameter. If needed you can do so in pycsw/ogc/api/records.py (Line 1150).

Populate the parameter from record imports

We have 2 options here, either manage the population of the column within the database as part of an insert trigger on the record.themes field. Alternatively update pycsw/core/metadata.py so the column is populated when records are imported.

For the second option consider the following code. For each of the keyword blocks, it tries to match the thesaurus title or uri and, if matched, adds the keywords to the new parameter.

_set(context, recobj, 'pycsw:InspireTheme', ", ".join(
    [", ".join(k.name for k in t.keywords if k.name not in [None,'']) for t in md_identification.keywords if ( hasattr(t,'thesaurus') and 
        t.thesaurus not in [None,''] and ((
            'title' in t.thesaurus and t.thesaurus['title'] not in [None,''] and
            t.thesaurus['title'] in ['GEMET - INSPIRE themes, version 1.0','GEMET Themes, version 2.3']
        ) or (
            'uri' in t.thesaurus and t.thesaurus['uri'] not in [None,''] and
            t.thesaurus['uri'] == 'http://inspire.ec.europa.eu/theme')))]))

Facets enable to further limit search results. Keywords from thesauri are very useful to add as facet. Add the paremeter to default.yml.

facets:
    - type
    - inspiretheme

Using keywords from a thesaurus as queryables