The Employee constructor is: 
sub new {
    my $class = shift;
    my $self = $class->SUPER::new();
    $self->{SALARY} = undef;
    $self->{ID} = undef;
    $self->{START_DATE} = undef;
    bless ($self, $class); # reconsecrate
    return $self;
}

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When you do 
my $emp = Employee->new;

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the $self returned by 
my $self = $class->SUPER::new();

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will be blessed into the Person package, so to be able to call the methods that Employee has beyond those in Person, $self needs to be reblessed into the class that Employee::new was invoked on (i.e. Employee or a subclass of it).

Update

The answer above would apply if the first version of Person::new() in perltoot (i.e. the one that doesn't bless $self into $class) were being used. As ikegami points out, the rebless isn't needed if Person::new() does bless $self into $class.

In reply to Re: To bless or not to bless by Arunbear
in thread To bless or not to bless by LesleyB

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