Clarify foreign key field in the docs

[dan-odsc]

1, I don't really understand the service at location appearing in the schedule table. Is that simply to allow an application to automatically set up a schedule without the user needing to add anything further i.e. a default from the service?

I think there is confusion around fields that end with “_id” which are foreign key fields existing on the schedule table. For the API/JSON representation, these are not required and are only needed with the tablular datapackage representation. We should aim to make that clearer in the docs.

The standard, for a long while, has given the flexibility for a service, service at location, and a location to have a schedule and a given schedule can only attach to one of these at a time.

Within the JSON/API representation these are nested under each object meaning there is no need to add these id fields, however for the tabular representation they are needed as foreign keys.

Action - 'Clarify foreign key fields' in the docs.