![]() ![]() Once the page has loaded, you’re usually presented with a form that allows you to enter your credentials, or in other words the information that you used to sign up for the site. So what actually happens when you arrive on the login page for your favorite website? That’s exactly what a sequence diagram is designed to show. Behind the scenes, any login page involves messages being sent back and forth, objects being activated, and responding with data, and it happens over a discrete period of time. How can you create a sequence diagram for a login system?Ī great example of sequence diagrams is a user login system. For much more detail, you should check out our sequence diagram page on Gleek. That gives you an overview of what to expect from a sequence diagram. The arrows are usually labeled so that you can easily understand the content of the message. Messages can be sent back and forth, from left to right, and the arrow shows which is the receiver and which the sender of the message. These messages are represented by a line with an arrow. Each object can also have an activation bar on its lifeline that will show when it is active in the system and accepting or processing information from another object.Īctivity in the system is shown by messages that pass between the objects. These lifelines are shown by parallel vertical lines that can never overlap. Each object has a lifeline that represents its existence in time. The diagram shows the objects, or actors, involved in the system. Make your own UML sequence diagram with Gleek. ![]() The sequence diagram lets a developer sketch out and demonstrates how processes will behave and interact in sequence. Also check out this comprehensive Sequence Diagram Tutorial to learn more about sequence diagrams.What is a sequence diagram and what is it used for?Ī sequence diagram is a type of UML (Unified Modelling Language) diagram that is used to model interactions between objects in a system over time. As always, we do encourage you to get in touch with us with any feedback or queries that you may have. What we have covered here are the basics of the sequence diagram, which should allow you to model most of the interactions that will take place in a common system. Inside the frame’s content area the loop’s guard is placed towards the top left corner, on top of a lifeline. You draw a frame, and in the frame’s namebox the text “loop” is placed. The loop combination fragment is very similar in appearance to the option combination fragment. In UML 2, modeling a repeating sequence has been improved with the addition of the loop combination fragment. This is something that is used when you need to model a repetitive sequence. Loops are rather basic and easy to grasp. If the student’s past due balance does not equal zero, then the sequence skips sending any of the messages in the option combination fragment. We include a guard for the option however, the guard is not a required element. According to the diagram, if a student’s past due balance equals zero, then the addStudent, getCostOfClass, and chargeForClass messages are sent. The image below uses an option combination fragment since a lot of messages have to be sent if the student’s past due balance is equal to zero. An option is usually used to model a simplistic “if then” statement, for example, if there are less than five donuts present on the counter, then make two dozen more. ![]() The option combination element or fragment is utilized to model a sequence that will occur provided it is given a certain condition. The word “alt” is placed inside the frame’s name box. As you can see below, will notice that an alternative combination fragment element is drawn using a frame. Alternatives allow the modeling of the “if then else” logic (e.g., if you were to buy three items, then you get 20% off your purchase whereas you get 10% off your purchase). This type of elements is utilized to indicate a mutually exclusive choice that exists between more that one message sequence. These would consist of Alternatives, Options and Loops. In this concluding post, we will take a look at the elements known as Combined Fragments. Lifelines, Messages and Guards) that were related to Sequence Diagrams. As we mentioned in the last post – The Basics and Purpose of Sequence Diagrams ~ Part 1, we did discuss three of the main elements (i.e. ![]()
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