Sequence Diagrams

Sequence diagrams are one of the most popular diagram types that are used to analyze and understand a certain solution.Basically speaking , sequence diagrams show the sequence.

UML diagrams can be used to model.
1 Usage Scenarios : This a description of a way a system maybe used.
2.The logic of methods : explore the logic of a certain operation
3.The logic of services : A service is a high level method.The logic of these methods may also be explained using sequence diagrams.

Lets start with the basic elements that need to be used when drawing a sequence diagram.

The above table describes the basic elements that are needed to draw a sequence diagram.

To draw a sequence diagram, we should first understand the scenario / system step by step.

http://www.developer.com/img/articles/2003/09/22/UML/UML0803.gif

The above image shows a sequence digram which is very simple.I have specified the link as well,because the diagram is not very clear.

While looking at the diagram, one thing to notice is,the difference in arrows. (the response arrows are broken lines,and the arrow head is different as well).This is something I used to miss.