 -- corpora
 -- each corpus has a unique name
 -- corpora are ordered in a tree
+DROP TABLE IF EXISTS _corpus;
 CREATE TABLE _corpus
 (
 	id 			numeric(38) NOT NULL,		-- primary key


-- source texts
-- stores each source text in its entirety
CREATE TABLE _text
(
	id 		numeric(38) NOT NULL,			-- primary key


-- node annotations
-- unique combinantion of node_ref, namespace and name
DROP TABLE IF EXISTS _node_annotation;
CREATE TABLE _node_annotation
(
	node_ref	numeric(38)	NOT NULL,		-- foreign key to _node.id
