PostgresSQL Table Schema

CREATE TABLE IF NOT EXISTS document (
 	_id SERIAL NOT NULL,
 	text_id TEXT UNIQUE NOT NULL,
 	length DOUBLE PRECISION NOT NULL,
 	parent_doc INTEGER,
 	"type" SMALLINT NOT NULL DEFAULT 1,

 	PRIMARY KEY (_id)
 );

CREATE TABLE IF NOT EXISTS term (
	_id SERIAL NOT NULL,
	term TEXT UNIQUE NOT NULL,

	PRIMARY KEY (_id)
);

CREATE TABLE IF NOT EXISTS gram (
	gram_id SERIAL NOT NULL,
	term_id_1 INT NOT NULL,
	term_id_2 INT,

	PRIMARY KEY (gram_id, term_id_1, term_id_2),
	FOREIGN KEY (term_id_1) REFERENCES term(_id),
	FOREIGN KEY (term_id_2) REFERENCES term(_id)
);

CREATE TABLE IF NOT EXISTS tf (
	gram_id INTEGER NOT NULL,
	doc_id INTEGER NOT NULL,
	lnc DOUBLE PRECISION NOT NULL,

	PRIMARY KEY (gram_id, doc_id),

	FOREIGN KEY (doc_id) REFERENCES document(_id)
);

CREATE TABLE IF NOT EXISTS idf (
	gram_id INT UNIQUE NOT NULL,
	df BIGINT NOT NULL
);