What is illustrated in a UML sequence diagram?

What is illustrated in a UML sequence diagram?
Answer: Sequence diagrams in the UML are primarily used to model the interactions between the actors and the objects in a system and the interactions between the objects themselves. A sequence diagram shows the sequence of interactions that take place during a particular use case or use case instance. The UML has a rich syntax for sequence diagrams, which allows many different kinds of interaction to be modeled. The objects and actors involved are listed along the top of the diagram, with a dotted line drawn vertically from these. Interactions between objects are indicated by annotated arrows.