The Schema-in PostgreSQL DDL

CREATE TABLE Categories

(cat_id SERIAL PRIMARY KEY,

cname VARCHAR(12));

CREATE TABLE Refs

(ref_id INTEGER PRIMARY KEY,

authors VARCHAR(100),

title VARCHAR(50),

link VARCHAR(100));

CREATE TABLE Users

(uid CHAR(12) PRIMARY KEY,

email VARCHAR(50));

CREATE TABLE Tests

(test_id SERIAL PRIMARY KEY,

ref INTEGER REFERENCES Refs (ref_id),

cat SMALLINT REFERENCES Categories (cat_id),

sn FLOAT NOT NULL,

sp FLOAT NOT NULL,

uid CHAR(12) REFERENCES Users (uid),

t_stamp TIMESTAMP DEFAULT CURRENT_TIMESTAMP,

approved LOGICAL);