UML sequency diagram is one of the structural type in diagrams of Unified Modeling Language.
Unified Modeling Language or UML is a general-purpose, developmental, modeling language in the field of software engineering that is intended to provide a standard way to visualize the design of a system. Unified Modeling Language has many types of diagrams, which are divided into two categories. Types represent structural information, and the general types of behavior, including a few that represent different aspects of interactions.
UML Sequence Diagram shows object interactions arranged in time sequence. It depicts the objects and classes involved in the scenario and the sequence of messages exchanged between the objects needed to carry out the functionality of the scenario. Sequence diagrams are typically associated with use case realizations in the Logical View of the system under development. Sequence diagrams of Unified Modeling Language (UML) are sometimes called event diagrams or event scenarios.
Sequence Diagram in UML shows, as parallel vertical lines (lifelines), different processes or objects that live simultaneously, and, as horizontal arrows, the messages exchanged between them, in the order in which they occur. This allows the specification of simple runtime scenarios in a graphical manner.