Beginner hoping for general help - Long

Question

Forgive the intrusion on this particular board, but I am not at all learned when it comes to databases and distributed computing, despite the fact I hold a degree that says I should be.
In short, I coded an application for my father's accountancy practice some years ago now. He now wishes to deploy it in a server-client manner (up to 4 offices (all with closed networks - each office would have separate data), ~5 employees each using it at once at each office). Basically, I have no idea how to do this. I could create a TCPclient and server module to 'pool' data on a server and distribute it, but no doubt it will end up being erroneous and slow. Henceforth, I assume the best way to go about this is to incorporate some form of database. (Data is currently just held in a simplistic fashion on each local machine, read line by line into the program, any more than 100,000 concurrent records is pretty slow).
However, I have a number of queries regarding this whole process.
I have no idea (at all) how best to even start, despite looking over the tutorials on this site. Do I need to get my hands on a database driver thing (technical) like Oracle or Cloudscape? What I basically want is a database driver which can be distributed with the application onto a number of client machines, as well as a server version. The clients can connect to the server to retrieve current data, and add to it across a closed network.
The other offices would be charged (not much at all - they are 'friends' - my budget for this whole thing is 1000 UK pounds or around $1800...) so I guess I need to purchase licenses if I use oracle or cloudscape. Am I likely to be way out of budget? I was looking on the Oracle site, but did not even know which product I needed to achieve my goals. (They were mind-blowingly expensive either way, but as I have said, my knowledge in this area is pathetic and hence I have no idea of the value of these products).
I hope my queries are clear. Since I don't really know what it is I want within the context of 'networking', it is hard to explain my requirements.
Thank you in advance.

Answer 1

Hi.
It is unlikely you need to pay for a database. You can use free databases like MySQL ( http://www.mysql.com ) if you want a relational database. Or you could use Prevayler ( http://www.prevayler.org ) if you want to avoid object to relational mapping and if you can hold the entire object graph of your system in the server's memory. There are also many other free solutions like McKoi ( http://mckoi.com/database/ ). These are all good.
There is no reason for the client/server interaction to be slow if you get the granularity of communication right. In general, avoid lots of small grained interactions. However, the best way to understand what is a good level is to try it and be prepared to refactor. Above all, don't design for assumed performance characteristics - experiment.
One question that might affect your design decisions significantly, however, is the type of connections that your offices have; if they have a dial-up, you probably want to minimise client/server interactions. If they have a permanently-on connection, then you have more freedom.
Regards,
Lance