Plain text "database" with multiple users

[Héctor Abreu]

Hi there,

I'm trying to test a plain text database with multiple users accessing
the same text file (the database). The context is like this:

1) Users access a GNU/Linux server via SSH. I'm using GNU Recutils for
reading/writing on the database, but I guess it won't be much difference
if a different software is used.

2) A particular user creates a plain text database for everybody's use.

3) I guess restrictions for reading/writing on the database will need to
be done through Unix/Linux groups.

My question is: How can be a text file (the database) can be restricted
so that users can only read/write what they're supposed to, without
messing with database structure or other users' sensitive info?

Will this restriction require an indirect interaction with the textfile
by the users? For example, allowing users to read only the results of
their queries rather than viewing the whole plain text file, or allowing
only the library (recutils, etc.) to write on the plain text file rather
that allowing users to edit directly the text file directly.

I'm new to this, sorry if I'm not making sense, but basically I'd like
to know how permissions on a plain text database can be handled with
mutiple users in a Unix/Linux environment, since the "database" is just
a plain text file.

Thank you in advance for any hint or help, even if it's a totally
different approach.

Regards,
--
Héctor Abreu