What do you think about this? We forgot about course category....

/**
 * Adds a new course to the course table
 *
 * @private ?
 *
 * @param array $course
 * $course format:
 * <ul>
 * <li>$course[name]</li>
 * <li>$course[shortname]</li>
 * <li>$course[format]</li>
 * <li>$course[idnumber]</li>
 * <li>$course[category]</li>
 * </ul>
 *
 * @return int|boolean new course id or false
 */
function add_course($course){
}

/**
 * Adds several new courses to the course table
 *
 * @param array $courses
 * $courses format
 * <ul>
 * <li>$courses[i][name]</li>
 * <li>$courses[i][shortname]</li>
 * <li>$courses[i][format]</li>
 * <li>$courses[i][idnumber]</li>
 * <li>$courses[i][category]</li>
 * </ul>
 *
 * @uses add_course
 *
 * @return array|boolean array containing new courses ids or false
 */
function add_courses($courses){
}

i think the course category should be passed by unique identifier (id, name), and have functions, like add_course, to course_categories too (I.E. add_course_category, delete_course_category, ... )
If no category parameter not specified, pass to a default category (0) ...

In the function thats remove a course_category, could have a flag(true/false), like cascade, thats set to do a delete cascade, removing all courses with associate couse_categories if it's set to true, the default could be false.

This funcionality is completed in CVS.
We have commit a simpletest.