Tag extras

[davidread]

CKAN has the 'tag vocabularies' feature, which allows you to create a list of tags that are attached to a 'vocabulary'. It seems a bit limited that the tag is only a name and no other properties. I'd like to add a 'display_name' which is the human-readable version of the tag, a 'uri' for it, 'broader' and 'narrower' references to create a tag hierarchy, and basically all the usual sort of vocab stuff you see in skos. This is so I can import some skos vocabularies and use them in CKAN.

I'd have thought we could create a TagExtras object to cover this.

[davidread]

Here are some messages about the current limitations for this sort of thing:

https://lists.okfn.org/pipermail/ckan-dev/2013-August/005710.html

[davidread]

Meeting is positive about having Tag Extras.

Debate how to store in the db:

• table (like PackageExtra) - I think it is valuable to be able to do postgres filter queries by each field - e.g. finding a tag with a particular URI, or all tags which are 'narrower' than another tag in a hierarchy. @wardi said it would have been wasteful for resources in his case where there are lots of extras that just need displaying.
• JSON blob in text column (like ResourceExtra) - this was used for resources with a view to using the Postgres JSON type in the future. I understand that the only sensible way to filter on a ResourceExtra is by doing SOLR queries, having set-up your field to be indexed separately. So not very flexible until it is converted to a Postgres JSON field.
• Postgres JSON field - requires Postgres 9.3+ and SQLAlchemy 0.9. Currently CKAN uses Postgres 8.4+ and Ubuntu 12.04 gives 9.1 and Ubuntu 14.04 can give 9.4. CKAN currently uses SQLAlchemy 0.7.8 and since Jan works in 0.8.4 and it's almost working with 0.9: https://github.com/ckan/ckan/pull/1817