Complex sentence: Mullingar is mentioned in the song "The Rocky Road to Dublin" by "The Dubliners", which is one the few songs in the 2009 film, "Sherlock Holmes" that was not composed for the film.
Split into simpler sentences: Mullingar is mentioned in the song "The Rocky Road to Dublin" by "The Dubliners". It is one the few songs in the 2009 film, "Sherlock Holmes" that was not composed for the film.