articles {
   id INTEGER UNIQUE NOT NULL AUTOINCREMENT
   message_id VARCHAR(255) UNIQUE NOT NULL
   date DATE NOT NULL
   header MEMO NOT NULL
   body MEMO NOT NULL
}

article_groups {
   article_id INTEGER REFERENCES articles.id
   group_id INTEGER REFERENCES groups.id
}

groups {
   id INTEGER UNIQUE NOT NULL AUTOINCREMENT
   name VARCHAR(255) UNIQUE NOT NULL
   creation_date DATE NOT NULL
   first_article INTEGER
   last_article INTEGER
   last_article_date DATE
}