MS SQL 2005 Express DB design question. Please help.

Hi all! I was given the task by my father who wants me to create an appointment DB for his new law firm and I can't seem to figure out what to do with the Appointment table. I've been stuck on this problem for well a week trying to google the answer to no avail.

Here's my design so far:
I have created 3 tables. One for Employees, one for Clients and one for Appointments(going to trials, meeting with the clients etc). The Employees table has the EmployeeID as the primary key and the Clients table has the Telephone as the Primary Key. The Appointment table has two foreign keys and no Primary key with one FK linking to the Clients_Telephone and the other FK linking to the Employee_EmployeeID.

What I want to accomplish:
A client calls and wants to set an appointment, the receptionist will take the information and query the appointment table to see if one of the partner named Anderson is busy at, say, 3:00PM to 4:00PM on a certain day. If he is then the information will not be applied and my GUI interface will display an error, if he is available then the information is set into the table.

I think I'm to use Domain Constraint, but the logic is very fuzzy to me. Thanks!One bit of advice. do not use the phone number as a PK. it can change. As this may be OK for some because all of the FKs can be updated what happens if you have to recover data from a backup into a production database and you can not overwrite the whole database. In this case you need to have primary keys that do not change to match up the records.|||@.Thrasymachus:

Thanks for your advice. I was thinking about using something other than a phone number like a driver's license or SS#, but I think it's unorthodox to ask them to provide such information. Don't you think?|||This is what I would do. Keep your primary on phone number, but add an identity field to cya.|||Any way you can link to an Exchange server, and use their appointment/meeting functonality?