I figured out how mySQL will work. As admin, Timothy has a userid and password that grants him access to the database. He needed that when he installed SMF. I'm admin on my test site, and I verified this. A program establishes a connection by providing the host (usually named localhost), the userid, and the password. The program can then access and update existing databases (providing the user has the necessary permissions), and also create new databases.
I plan to try this (none of this involves the forum's database):
1. Maintain a signature database table, one row per user. If the database doesn't exist, the program creates it.
2. users sign into the signature tool. No password is needed, just a userid. Once they've done that the first time, the program remembers them in a cookie. Nothing we store will be sensitive, so I don't think a password is needed.
3. The signature tool uses userids as the primary key to the database to retrieve and update records. Each user has one record that has in its fields the user-oriented data we need to maintain: banner url, author name, BBCode text and links, and so on.
This way, their data go with them wherever they go, which has been one of my main concerns about using cookies.
I'll work probably next week to get it up and running.
To install the program with another forum, such as WS, the admin will provide the userid and password that the program uses to access the database. We can rig it so nobody else sees those access data.
This is me speculating. MySQL looks like a lot of relational databases I worked with in the old days. It shouldn't be difficult to work with. I hope.
Anybody out there with SQL chops should chime in if I'm heading in the wrong direction. Wish me luck.