Sequence diagrams

Sequence diagrams are used to show a specific use case scenario. So, these diagrams are representative of a typical behavior based on the given use case.

The following sequence diagram example visually documents the use case where a student logs on to an online book order system and enters their course code. The online system calculates a price and provides this total to the student. The student is then able to submit their payment, which goes through the online bookstore and informs the fulfillment center, which ships the books to the student: