B.7.1. Direct System Database Access
Perl can directly access some system databases, sometimes with the help of a module. These are databases like the Windows Registry (which holds machine-level settings), or the Unix password database (which lists which username corresponds to which number, and related information), as well as the domain-name database (which lets you translate an IP number into a machine name, and vice versa).
B.7.2. Flat-file Database Access
If you'd like to access your own flat-file databases from Perl, there are modules to help you with doing that (seemingly a new one every month or two, so any list here would be out of date). You can even do quite a bit without a module, with what we give in Chapter 16, "Simple Databases".
B.7.3. Relational Database Access
Relational databases include Sybase, Oracle, Informix, mysql, and others. These are complex enough that you generally do need to know about modules to use them. But if you use the DBI module, whose name stands for "database-independent," you can minimize your dependence upon any one type of database -- then, if you have to move from mysql to Oracle, say, you might not even need to change anything at all in your program.
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