Ding Dong the witch is dead ------- what does it mean ?

“Ding Dong! The Witch is Dead” is a song in the 1939 movie The Wizard of Oz 綠野仙蹤 sung by the munchkins in response to hearing the death of the Wicked Witch of the East 東方的壞巫婆.
From http://en.wikipedia.org/wiki/Ding-Dong!_The_Witch_Is_Dead

Lyrics of Ding Dong! The Witch is Dead!
Ding Dong! The Witch is dead. Which old Witch? The Wicked Witch!
Ding Dong! The Wicked Witch is dead.

Wake up - sleepy head, rub your eyes, get out of bed.
Wake up, the Wicked Witch is dead. She’s gone where the goblins go,
Below - below - below. Yo-ho, let's open up and sing and ring the bells out.
Ding Dong the merry-oh, sing it high, sing it low.
Let them know
The Wicked Witch is dead!

When people use it, it can mean they are happy because something favorable for them has happened.
eg. Both A and B want to become school captain. But A found out that B was caught stealing. A says to his friend, “Ding Dong! The Witch is Dead! I can’t believe B would steal, now I’ll have no opponent.”

2006-10-26 18:54:41 補充：
Ding Dong is not the name of the witch. Ding Dong is the sound of bells ringing as seen in the lyrics.

Ding Dong the witch is dead. - 女巫叮噹己死