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Sequence Diagram


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A Sequence Diagram is an Object Diagram that describes object interaction. Objects are shown at the very top from left to right, while the time flows from top to bottom. Arrows indicate messages and other interactions between objects.

The official UML definition for Sequence Diagram is: A diagram that shows object interactions arranged in time sequence. In particular, it shows the objects participating in the interaction and the sequence of messages exchanged. Unlike a collaboration diagram, a sequence diagram includes time sequences but does not include object relationships. A sequence diagram can exist in a generic form (describes all possible scenarios) and in an instance form (describes one actual scenario). Sequence diagrams and Collaboration Diagram s express similar information, but show it in different ways.
See also: Collaboration Diagram and InteractionDiagram
Use Cases And Sequence Diagrams
Sequence diagram tutorial

Sequence Diagrams is about the only type of documentation defined by UML that I really struggle with. I can interpret these diagrams just fine - with a book in front of me. But I can't seem to natively think in terms of a Sequence Diagram, or visualize it in my head rather, when in the design and planning phase of a project. I think maybe I dont understand their purpose. Can somebody tell me how they put Sequence Diagrams to use or in what way they find them useful? - Roxanne Seibert

Sequence Diagrams are real easy if you have good ToolSupport. Unfortulately, anemic old Visual Modeler doesn't do Sequence Diagrams, nor any other of the more useful UML diagrams.

Using Rational Rose, you can lay out instances of classes, and link them with arrows that abstractly represent messages. For example, we could say that "in this scenario, this object will send a message to the application object". Later, you can rightclick the arrow and pick or enter a method name. If the method doesn't exist, you can define it right there.

Thus at one level of analysis you can say, "We'll get this info from somewhere, say the application object". The important thing being that the info will come from somewhere. Later, when you are actually designing the interfaces, you can put a method name on the message. Any changes made in the classes present in the Sequence Diagram are kept concurrent throughout the model by Rose. This is very slick
-- Steven Black

The support for sequence diagrams in the current release of Visio Enterprise is not as strong as Rational Rose. You can refer to operations of instances that don't exist in the class but this doesn't add the operation to the class. As for support for sequence diagrams in the next relase of Visio Enterprise, I can't say. -- ?jMM

There is a Visio Shape Sheet downloadable from www.navision.com/services/methodology/stencil.asp that has some good shapes defined for representing sequence diagrams. Along with that they have a document, www.navision.com/services/methodology/UML_Tips.asp that is very helpful. I am with Roxanne, sequence diagrams are easy to read and hard to create.-- Pamela Thalacker

An excellent alternative to Rational Rose and Visio is VisualUML. Much less expensive than Rose and has full round-trip functionality. -- Alex Wieder

You can check out Visual UML at Markus Egger's EPS-Software. They distribute the product and are responsible for the VFP round-trip portion. -- Alex Feldstein
Contributors: Steven Black jMM Roxanne Seibert Pamela Thalacker Alex Wieder
Category UML, Category Modeling
( Topic last updated: 2004.01.22 12:14:48 PM )