def etl(db_engines):
    # Extract the data
    courses = extract_course_data(db_engines)
    rating = extract_rating_data(db_engines)
    # Clean up courses data
    courses = transform_fill_programming_language(courses)

    # Get the average course ratings
    avg_course_rating = transform_avg_rating(rating)

    # Get eligible user and course id pairs
    courses_to_recommend = transform_courses_to_recommend(
        rating,
        courses,
    )

    # Calculate the recommendations
    recommendations = transform_recommendations(
        avg_course_rating,
        courses_to_recommend,
    )

    # Load the recommendations into the database
    load_to_dwh(recommendations, db_engine))