CREATE TABLE departments (
   department_id INTEGER UNIQUE NOT NULL, 
   ...
CONSTRAINT departments_pkey_department_id PRIMARY KEY (department_id)
)

CREATE TABLE item_templates (
    item_template_id INTEGER UNIQUE NOT NULL,
    department_id INTEGER NOT NULL,
CONSTRAINT item_templates_pkey_item_template_id PRIMARY KEY (item_template_id),
CONSTRAINT item_templates_fkey_department_id FOREIGN KEY (department_id) REFERENCES departments (department_id) ON DELETE CASCADE
)

CREATE TABLE item_instances (
     item_instances_id INTEGER UNIQUE NOT NULL,
     item_template_id INTEGER NOT NULL,
CONSTRAINT item_instances_pkey_item_instances_id PRIMARY KEY (item_instances_id),
CONSTRAINT item_instances_fkey_item_template_id FOREIGN KEY (item_template_id) REFERENCES item_templates(item_template_id) ON DELETE RESTRICT
)