Design an ER (or EER) diagram based on the information given below.

A local dog trainer holds obedience classes Champaign, Urbana, and Savoy. She teaches all five levels in each city. She teaches five levels of classesBasic, Intermediate, and three advanced level classes (I, II, and III) in each city.

Each class is associated with a class level. Owners cannot enroll their dogs in the Intermediate class unless they have taken the Basic class, and they cannot be enrolled in any of the advanced classes they have taken the Intermediate class. The class level includes the name, description, and the prerequisite of the class. The trainer will never take more than eight dogs in a single class, and she will not cancel a class unless no one signs up for it.

The dog trainer requires that the database keeps track of information about each dog, the dog's owner, and each class. Owner information includes the name, address (street, city, state, zip), phone, and email address. Dog information should include the dog's name, birthday, breed, color (can have more than one color), and the dog's shot date. Class information should include the class identifier, the city, start and end dates, start time, class size (number of dogs attended).

In addition, the trainer keeps track of the different skills that the dogs can perform after each class (such as fetch, rollover, heel, etc.). For each skill learned, the trainer records the name of the skill and assigns a grade (good, fair, or poor), along with a date. The trainer can teach the same skill, at increasingly levels of difficulty in a variety of the courses. For example, fetch can be taught in the basic, intermediate and any of the advanced courses. Some dogs would need to the beginners class multiple times before she was ready to move to the intermediate class. The dog trainer is very patient with such dogs (and owners) and allows the dog to repeat a course until the dog learns the skills (or the owner give up). For most dogs the grade assigned for each skill within a course would improve with each iteration.