Questions about Database Implementation.

Metuchen asks: "I'm developing a program for Linux that will eventually be managing a medical practice. This program will be running on several terminals on the same computer, but they must all access the same database simultaneously (i.e. if one user were to update a record, the next time another user accesses that patient--on a different terminal--the correct information must be displayed). What would be the best way to implement such a program? I would prefer to stay away from writing everything to file after each update since the database will be updated frequently; for the same reasons, I would like to be able to keep everything in RAM without using a RAMdrive (since that may require up to one file per patient). Any suggestions?"