Allow organization and service_at_location to be categorised with taxonomy

[timgdavies]

At present service_taxonomy is used to related service objects to taxonomy objects, classifying a service.

From #154 via @klambacher:

To my knowledge, categories would not be required to describe locations so location_id is not required, but I certainly wouldn't object to seeing that option. I have also seen a requirement to classify organizations for some use cases, so an organization ID would be a good option as well.

This suggests either:

• Introducing a parallel 'service_at_location_taxonomy' (or just 'location_taxonomy') table, and 'organization_taxonomy' table; or
• Renaming 'service_taxonomy' to 'taxonomy_link' and including multiple possible identifier columns for service_id, location_id and organization_id

Views on the use-cases and approaches to be taken here would be welcome.

[NeilMcKLogic]

@timgdavies , I agree with @klambacher. I prefer your second approach of "taxonomy_link". But since 1.1 is approved I would think this would need to be in a future rev of the spec.

[boxfoot]

@klambacher could you share a bit more about the use case for this? Under what circumstances would a service-at-location need to have different taxonomy codes applied than the underlying service itself?

[MikeThacker1]

I've raised this as a more general need for taxonomies for multiple types of entity as issue 208.

[robredpath]

MINOR - adding lots more tables

MAJOR - adding a more expressive taxonomy mechanism and using it in more places, with better names and terminology

[mrshll1001]

Closed. See #208, we can attach taxonomies and attributes to most objects/schemas now :-)