Errata

The Y column of the rightmost table is lacking a double underline.

Delete this bullet item

In Fig. 7.5, the table showing the transitive closure TC appears to be missing the following entry:

P1 P6

Here is a little Perl script that shows the correct output, albeit in an order that does not match Fig. 7.5:

$ perl erratum.pl

PP
____ ____
| PX | PY |
|____|____|
| P1 | P2 |
| P1 | P3 |
| P2 | P4 |
| P3 | P4 |
| P4 | P5 |
| P5 | P6 |
|____|____|


TC
____ ____
| PX | PY |
|____|____|
| P1 | P2 |
| P1 | P3 |
| P1 | P4 |
| P1 | P5 |
| P1 | P6 |
| P2 | P4 |
| P2 | P5 |
| P2 | P6 |
| P3 | P4 |
| P3 | P5 |
| P3 | P6 |
| P4 | P5 |
| P4 | P6 |
| P5 | P6 |
|____|____|

$ cat erratum.pl
sub print_table {
my ( $pr_ref, $n ) = @_;

print "\n";
print "$n\n";
print " ____ ____ \n";
print " | PX | PY |\n";
print " |____|____|\n";
for my $px ( sort keys %{$pr_ref} ) {
for my $py ( sort keys %{ $pr_ref->{$px} } ) {
print " | $px | $py |\n";
}
}
print " |____|____|\n";
print "\n";
} ## end sub print_table

sub get_tc {
my ( $pp_ref, $tc_ref, $px_immediate, $py_immediate ) = @_;

for my $px ( keys %{$pp_ref} ) {
for my $py ( keys %{ $pp_ref->{$px} } ) {
if ( defined $tc_ref
&& defined $px_immediate
&& defined $py_immediate )
{
if ( $px eq $py_immediate ) {
$tc_ref->{$px_immediate}{$py} = {};
$tc_ref = get_tc( $pp_ref, $tc_ref, $px_immediate, $py );
}
} ## end if ( defined $tc_ref &&...)
else {
$tc_ref->{$px}{$py} = {};
$tc_ref = get_tc( $pp_ref, $tc_ref, $px, $py );
}
} ## end for my $py ( keys %{ $pp_ref...})
## end for my $px ( keys %{$pp_ref...})
} ## end for my $px ( keys %{$pp_ref...})

return scalar $tc_ref;
} ## end sub get_tc

my $pp_ref = {
P1 => { 'P2' => {}, 'P3' => {} },
P2 => { 'P4' => {} },
P3 => { 'P4' => {} },
P4 => { 'P5' => {} },
P5 => { 'P6' => {} },
};

print_table( $pp_ref, "PP" );

my $tc_ref = get_tc($pp_ref);

print_table( $tc_ref, "TC" );

Note from the Author or Editor:
On p 159 in the printed book, Fig. 7.5, table labeled TC should contain one additional row with PX = P1 and PY = P6.

In the sentence beginning "For one thing", replace "For one thing" by "To be specific". Delete the sentence beginning "For another" (including the immediately following SQL expression).

In the code lines beginning ON DELETE nls and ON INSERT nls, replace LS by NLS.

Replace "relvar S" by "relvar SC"

Replace "S" by "SC".

In lines 1, 4, and 7, replace "S" by "SC"

In lines 2 and 8, replace "S.*" by "*". In line 16, replace "S.SNO" by "SNO". In lines 3, 9, and 17, replace "FROM S" by "FROM SC".

In line 2, replace "features (see" by "features--see"