An example might be how a banking client interacts with an ATM to withdraw cash. Sequence diagrams are great at showing the interactions between elements in a system over time. Example: how to create a sequence diagram for an ATM withdrawal You can read more about the other types of messages and operators used in sequence diagrams in our detailed breakdown of how sequence diagrams work. We will use the alt operator in our example below. These guard conditions are interaction constraints that divert the flow of events depending on particular circumstances, such as whether a user has supplied the correct password. The operator might be alt/else, if there is a choice between multiple operands, opt, if there is a choice between two operands, and the condition is either met, or not met. The fragment is marked by an operator in the top-left corner.

These act as frames for parts of an interaction. You can depict complex interactions between multiple objects in the sequence diagram by using sequence fragments. The arrows descend in the order in which the events they represent occur. These arrows actually depict messages in the system and the style of arrow tells you whether the messages are synchronous, asynchronous, or whether the message creates or deletes objects in the system. The interactions between them are represented by horizontal arrows that can go from left to right and vice versa. The objects, or actors, are shown at the top of the diagram as named rectangles.Įach object has a vertical lifeline descending from it to show the different processes that exist simultaneously in the system during the time period captured by the diagram. Sequence diagrams descend from top to bottom to show the sequence of interactions. Also called event diagrams or event scenarios, sequence diagrams depict the sequential events that occur and the processes that are completed.

Sequence diagrams show an overview of the interactions between objects in a system over time. What is a sequence diagram and what is it used for?

Sequence diagram online shopping system