Narrative opening: A narrative opening is when you are introduced into the film where the credits are played during the opening of the film. The scene is set with a narrative opening this gives you an insight of the film and the credits just run through out the opening there is a example of a narrative opening above from the film 'The Shinning'.
Discrete Title Sequence: A discrete title sequence is a small self detained film, which is a opening of a film which is usually different form the film doesn't have any relevance towards the film and doesn't relate at all. There is a example above of a discrete title sequence from the film 'SEVEN'.
Titles over a blank screen of a narrative opening: This is just a narrative opening with titles over a blank screen as shown in 'Donnie Darko'.