Excellent point, Apotheon. You helped me see relationships in my own writing and software design styles. I'd never consciously related the two processes this way. In short:

Sequence diagram <--> Outline of book/article/etc

Object diagram <--> Character/Event diagram

With sequence diagrams, one can represent possible variations in flow. Object diagrams are a good way to represent characters, their relationships, and effects of events between them. Perhaps schema would be a better term for this instead of object diagram.

Thanks, Apotheon!