The line symbol describes this with the text >. In the use case below, the Login action needs to use the Verify Login Credentials to execute its intended task.Īlso, use case diagrams have a symbol that describes how an action can enhance the behavior of another action. Use case diagrams have a symbol that describes a separate action required by a particular action. Top considerations for building a modern edge infrastructure.How to explain edge computing in plain English.Activity symbolsįigure 2 describes the symbols used in the activity diagram illustrated in Figure 1. At that point, the activity diagram describes a set of simultaneous actions on the webpage: playing the video while also displaying the video catalog where a user can select another video to view, which interrupts the current video running.Īt any point during the viewing process, the user can log out of the website. (The sign-up option is implicit and not illustrated in the diagram.) The Unknown User page provides the option to sign up for the service. Otherwise, the user is redirected to an Unknown User page. That user is then allowed to view a list of videos on a catalog page. The diagram describes a user logging into the site and being subjected to verification at a decision point. Activity exampleįigure 1 is an activity diagram describing the flow of activities executed in an instructional video website.įigure 1: UML activity diagram click to enlarge (Bob Reselman, CC BY-SA 4.0) Activity diagrams are perfect for describing how a system operates on a step-by-step, condition-by-condition basis. Also, an activity diagram can describe simultaneous activities, decision points, and subsequent behavior based on the decision's result. ActivityĪn activity diagram describes the flow of actions in a system or subsystem. The following sections describe the details of each type of dynamic diagram. UML specifies seven types of dynamic diagrams: A static diagram, on the other hand, describes the characteristics of a system or part of a system. A dynamic diagram describes the operations, actions, and changes that occur in a system over time. Types of dynamic diagramsĭynamic UML diagrams describe the behavior of systems. That application is a system that delivers an educational video to a user according to a selection made from a catalog of videos available for viewing. In this article, I go into the details of dynamic diagrams, and in another article, I explain static diagrams.Įach example diagram for this article represents a particular aspect of a hypothetical application called the Instructional Video Service. My introductory article answers essential questions like: What is UML? Why was UML created? Who created UML? and Why should you use UML? There are two basic types of UML diagrams: static and dynamic.
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