Implement 'fragment' domain object

[pudo]

Fragment is another type of relation which can link to any number of entities through a piece of marked-up text. The reason for implementing this is to combine narrative elements into the database, so that you can capture non-structured parts of a story in a way that is easy to understand for readers.

The metaphor for this is the Facebook timeline, where each update would be shown on the feeds for all entities mentioned within. Subscriptions would help users make their own news feeds with the updates of all entities to which they are subscribed.

A domain model could look like this:

• fragment: has text, start_date, end_date, account_id, source_url.
• fragment_entity: has fragment_id, entity_id, text_start, text_end.
• entity_subscription: has account_id, entity_id, since_date (used to subscribe users to an entity's news feed - but do we want all subscribers to have to be users?)

There's a mockup of what the finished function could look like here: http://opendatalabs.org/misc/demo/grano/_mockup/