ALTER TABLE ADD COLUMN and add NOT NULL column without DEFAULT value is illegal in PostgreSQL:

https://stackoverflow.com/questions/3492947/insert-a-not-null-column-to-an-existing-table

Correct behavior should be default NULL instead.

As you can see browsing Cadmium shards source code, several entities (for lack of a better word) are declared in different locations and in different ways.

This issue is not just a namespace or redundancy issue but we'd benefit by having fundamental classes or structs describing the tokens, sentences and documents we're dealing with.

I've started in the pos_tagger declaring such structs an