Allow definition of Views in Datastore which are exposed as Computed Datasets

[jqnatividad]

Views are nothing more than stored queries.

Oftentimes, when uploading open data, publishers denormalize data in their transaction DBs into big, wide tables. Having views against these tables would make it easier for data consumers to digest the data.

It will also help with complex queries/joins across tables. And perhaps, for certain popular, expensive queries, materialized views can be used to increase performance.

[jqnatividad]

This can be done in coordination with #59, as some system catalog objects can just be views, similar to the way Oracle's system catalog is composed primarily of views.

If views are supported, maybe there can even be a way for CKAN extensions to register views (e.g. stats can add view/download metrics to the catalog; a geocoder extension can extend a dataset's metadata with geographical info, etc.)

[rufuspollock]

@jqnatividad have you seen #28 (custom data APIs) - do you think there is a connection here? Would this possibly be a subpart of #28?

[jqnatividad]

@rgrp I haven't seen #28 (custom data APIs) before I posted this, but yes, there is definitely a connection!

Perhaps, we can start showing the power of this approach with the System Metadata Catalog #59?

[rufuspollock]

@jqnatividad I'm suggesting to merge this with #28 - wdyt?

[jqnatividad]

@rgrp makes sense to me - merge away!

[rufuspollock]

DUPLICATE / MERGED WITH #28.