Keeping data private per User in a multi user database

Hello. I have an Accounting Access DB that I intend at some point to split
into front-end (tables, forms, reports) and back-end (data), then I hope to
deploy on the web. I will eventually have around 30 distributed users (only
about 5 concurrent) – each inputs the same type of financial data but does
business independent of the others and so must NEVER see the data entered by
the other users. To make future releases and bug fixes as simple as
possible, I intend to have a single instance of the front-end that each of
the Users will access.

However, as each User must NEVER see data entered by other Users, is there
any way of achieving ‘privacy’ for each User so they only ever see their own
set of data? My first reaction is that I must (in some way?) have multiple
instances of the back-end data base (remembering there is a common single
front end instance) and somehow ‘map’ each user to only ever open their own
back-end. However, I’m hoping there might be a more simple elegant way of
ensuring privacy perhaps by somehow (cleverly) making each set of User data
private to that User on a single instance back-end data base.

In a nutshell I’m asking how I’d configure Access to allow many users to
enter their own private data through a shared common single instance
front-end and keep their data private from other users.

I should finally add that I have just got to grips with Access and while
there may well be better more appropriate alternatives such as SQL or MySQL,
I’d much rather stick with Access – the user population won’t grow any more
than anticipated.

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Peter