  For an artinian ring $R$, the directed zero-divisor graph $\Gamma(R)$ is
connected if and only if there is no proper one-sided identity element in $R$.
Sinks and sources are characterized and clarified for finite ring $R$,
especially, it is proved that for {\it any} ring $R$, if there exists a source
$b$ in $\Gamma(R)$ with $b^2=0$, then $|R|=4$ and $R=\{0,a,b,c\}$, where $a$
and $c$ are left identity elements and $ba=0=bc$. Such a ring $R$ is also the
only ring such that $\Gamma (R) $ has exactly one source. This shows that
$\Gamma(R)$ can not be a network for any ring $R$.
