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A sequence diagram describes an interaction among participants using lifelines and ordered messages; time normally runs downward. Calls, replies, and execution intervals show a scenario such as the client asking a Sports wrapper for its cost, then that wrapper delegating through the inner packages to BasicPlan and adding charges on return. Alternatives or loops can describe more than one trace.

A state diagram describes states of an object or system and transitions triggered by events, possibly guarded by conditions and accompanied by actions. An account might move from active to suspended on a failed-payment event and back to active on payment. It describes allowed lifecycle behavior rather than the order of messages in one chosen interaction. Both are behavioral diagrams in UML.

A sequence diagram shows participants as lifelines and the order of messages between them, usually with time progressing downward. It can show a client asking a sports wrapper for its price, followed by nested calls through the other decorators to the basic component, then replies carrying the accumulated cost.

A state diagram shows the possible states of a system and event-triggered transitions, with optional guards and actions. For an account, it might distinguish active, suspended and closed states and the events allowing a change.

Both are behavioral UML views, but a sequence diagram emphasizes ordered interactions between participants; a state diagram emphasizes states and permitted transitions. A lifecycle state diagram can admit many different message traces.

Describe the possible states of a system and transitions triggered by events, optionally constrained by guards and accompanied by actions. The diagram emphasizes a component's lifecycle and permitted reactions. It can describe many interaction traces, while a sequence diagram focuses on the temporal ordering of messages in an interaction.

A modeling language for describing software structures and behavior. A class diagram records types and relationships; a sequence diagram records ordered interactions; a state diagram records states and event-triggered transitions.