If it was just me using the system then I'd simply enter them into one central file. However, as you want it to be really simple to use, then the database option is the way forward. You'll also want a set-up screen for them to enter their database details using an on-line form, as opposed to opening up a PHP file.

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The man who comes back through the Door in the Wall will never be quite the same as the man who went out.