Database ER diagram review. Is this a good database design?

Question

I have a task to design an ER diagram and task is given as points below is the description of the problem:

1. A telecommunications company employs thousands of consultants.
2. Each consultant is assigned to a company department, each department might be a part higher level company division up to the CEO board (multiple levels)
3. The personal data for each employee include:first name, last name, address, phone number and email
4. The company provides different types of services –online sales, advertising, maintenance, each employee has a specific primary and optionally secondary role assigned
5. The company collects information about clients including their personal data and also all signed contracts, sold devices and active premium services
6. Each contact with a customer is registered in dedicated service ticket including type of service (contract, issue, advertising), start and end date and customer id
7. The ticket tracks a progress of particular case by recording each activity performed by the employee using a specific type of activity, date, and arbitrarily long description
8. Each ticket has a status flag (e.g. registered, in progress) and for closed tickets the closure summary is added.

I designed an ER diagram and it is below my question. Is it a good idea to design point 8 where for closed tickets the closure summary is added. part via an optional summary table.

Looking for your advice. Also I am not sure if this is a good Database design I know it is a time taking task, but I really appreciate if someone can tell me "How good" my design is, and whether it requires any change. Thanks!

Answer 1

I figured my mistakes:

• Consultant is Employee. When I read the task I thoguht I have to create two different tables but no need for it so I simply removed the table CONSULTANT.
• Closure summary is a direct attribute of each ticket so there is no need to have another table for this. Added to the TICKET table as nullable field.
• A foreign key column with the UNIQUE and NOT NULL constraints that references a UNIQUE, NOT NULL column in another table creates a 1:(0|1) relationship, which is probably what you want.
• According to above Realtionships between Client and Signed Contract, Premium Service, Sold Device also Entry and Ticket realtionships are wrong. Fixed them accordingly

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