my %defaults = (
      data_source_name => ".....",
      username => "fred",
      password => "fred",
      taint => { Taint => 1 }
);

# then later...
%arguments = (%defaults, %arguments);

my $dbh = DBI->connect( @arguments{ qw(data_source_name 
                                 username password taint) }) 
          or die "Could not connect to the database: ".
                 "$DBI::errstr";