What is sequence diagram pdf

Note that: An actor does not necessarily represent a specific physical entity but merely a particular role of some entity A person may play the role of several different actors and, conversely, a given actor may be played by multiple different person. Lifeline A lifeline represents an individual participant in the Interaction.

Activations A thin rectangle on a lifeline represents the period during which an element is performing an operation. The top and the bottom of the of the rectangle are aligned with the initiation and the completion time respectively Call Message A message defines a particular communication between Lifelines of an Interaction.

Call message is a kind of message that represents an invocation of operation of target lifeline. Return Message A message defines a particular communication between Lifelines of an Interaction. Return message is a kind of message that represents the pass of information back to the caller of a corresponded former message. Self Message A message defines a particular communication between Lifelines of an Interaction. Self message is a kind of message that represents the invocation of message of the same lifeline.

Recursive Message A message defines a particular communication between Lifelines of an Interaction. Recursive message is a kind of message that represents the invocation of message of the same lifeline. It's target points to an activation on top of the activation where the message was invoked from. Create Message A message defines a particular communication between Lifelines of an Interaction. Create message is a kind of message that represents the instantiation of target lifeline.

Destroy Message A message defines a particular communication between Lifelines of an Interaction. Destroy message is a kind of message that represents the request of destroying the lifecycle of target lifeline. Duration Message A message defines a particular communication between Lifelines of an Interaction. Duration message shows the distance between two time instants for a message invocation. Note A note comment gives the ability to attach various remarks to elements.

Turn every software project into a successful one. Optionally, the shop will send the member a confirmation notification if the member opted for the notification option in the order. Visual Paradigm supports sequence diagram and other UML diagram types. You can find all the tools you need in modeling the dynamic behaviors of a system using sequence diagram. We use cookies to offer you a better experience. By visiting our website, you agree to the use of cookies as described in our Cookie Policy.

Object In the UML, an object in a sequence diagram is drawn as a rectangle containing the name of the object, underlined. Lifeline Entities of participants in a collaboration scenario are written horizontally across the top of the diagram. Message Messages depict the invocation of operations are shown horizontally. The line type and arrowhead type indicates the type of message being used: A synchronous message typically an operation call is shown as a solid line with a filled arrowhead.

It is a regular message call used for normal communication between sender and receiver. A return message uses a dashed line with an open arrowhead. An asynchronous message has a solid line with an open arrowhead. A signal is an asynchronous message that has no reply. Creation and Destruction Messages Participants do not necessarily live for the entire duration of a sequence diagram's interaction.

Non instantaneous message Messages are often considered to be instantaneous, thus, the time it takes to arrive at the receiver is negligible. Focus of Control Focus of Control represents the period during which an element is performing an operation. The top and the bottom of the of the rectangle are aligned with the initiation and the completion time respectively Iteration notation Iteration notation represents a message is sent many times to multiple receiver objects, as would happen when you are iterating over a collection.

Step 1 and 2: Customer creates an order. Step 3: Customer add items to the order. Step 4, 5: Each item is checked for availability in inventory.

Step 6, 7, 8 : If the product is available, it is added to the order. Step 9 return Step 10, save and destroy order Sequence Fragments In a UML sequence diagram, combined fragments let you show loops, branches, and other alternatives.

Operator Meaning alt Alternative multiple fragments : only the one whose condition is true will execute. Equivalent to an alt only with one trace. The frame is drawn to cover the lifelines involved in the interaction.

You can define parameters and a return value. Let's start with three simple examples. Figure 1 depicts a UML sequence diagram for the Enroll in University use case, taking a system-level approach where the interactions between the actors and the system are shown. Figure 2 depicts a sequence diagram for the detailed logic of a service to determine if an applicant is already a student at the university.

Figure 3 shows the logic for how to enroll in a seminar. I will often develop a system-level sequence diagram with my stakeholders to help to both visualize and validate the logic of a usage scenario. The sequence diagram represents the flow of messages in the system and is also termed as an event diagram. It helps in envisioning several dynamic scenarios. It portrays the communication between any two lifelines as a time-ordered sequence of events, such that these lifelines took part at the run time.

The reason why they're called sequence diagrams should be obvious: the sequential nature of the logic is shown via the ordering of the messages the horizontal arrows. The first message starts in the top left corner, the next message appears just below that one, and so on.

The boxes across the top of the diagram represent classifiers or their instances, typically use cases, objects, classes, or actors.

Because you can send messages to both objects and classes, objects respond to messages through the invocation of an operation and classes do so through the invocation of static operations, it makes sense to include both on sequence diagrams.

Because actors initiate and take an active part in usage scenarios, they can also be included in sequence diagrams. Classes have labels in the format ClassName , and actors have names in the format Actor Name.

Notice how object labels are underlined, classes and actors are not. For example, in Figure 3, you see the Student object has the name aStudent , this is called a named object, whereas the instance of Seminar is an anonymous object.

The instance of Student was given a name because it is used in several places as a parameter in messages, whereas the instance of the Seminar didn't need to be referenced anywhere else in the diagram and thus could be anonymous. Any message sent to a class is implemented as a static method, more on this later. The dashed lines hanging from the boxes are called object lifelines, representing the life span of the object during the scenario being modeled.

I will only draw activation boxes when I'm using a tool that natively supports them, such as a sophisticated CASE tool, and when I want to explore performance issues. Activation boxes are too awkward to draw on whiteboards or with simple drawing tools such that don't easily support them.

The X at the bottom of an activation box, an example of which is presented in Figure 4, is a UML convention to indicate an object has been removed from memory.

In languages such as Java or C where memory is managed for you and objects that are no longer needed are automatically removed from memory, something often referred to as garbage collection, you do not need to model the message.

I generally don't bother with modeling object destruction at all and will instead trust that the programmers, often myself, will implement low-level details such as this appropriately. Figure 4 presents a complex UML sequence diagram for the basic course of action for the Enroll in Seminar use case. This is an alternative way for modeling the logic of a usage scenario, instead of doing it at the system-level such as Figure 1 you simply dive straight into modeling the detailed logic at the object-level.

I'll take this approach when I'm working with developers who are experienced sequence diagrammers and I have a large working space either a huge whiteboard or a CASE tool installed on a workstation with a very large screen and good graphic card. Most of the time I'll draw system-level diagrams first and then create small diagrams along the lines of what is shown in Figures 2 and 3.

Messages are indicated on UML sequence diagrams as labeled arrows, when the source and target of a message is an object or class the label is the signature of the method invoked in response to the message. However, if either the source or target is a human actor, then the message is labeled with brief text describing the information being communicated.

Notice how I include both the method's name and the name of the parameters, if any, passed into it. The Student actor provides information to the SecurityLogon object via the messages labeled name and student number these really aren't messages, they are actually user interactions.

Return values are optionally indicated using a dashed arrow with a label indicating the return value. For example, the return value theStudent is indicated coming back from the Student class as the result of invoking a message, whereas no return value is indicated as the result of sending the message isEligibleToEnroll theStudent to Seminar.

My style is not to indicate the return values when it's obvious what is being returned, so I don't clutter my sequence diagrams as you can see, sequence diagrams get complicated fairly quickly. Figure 5 shows an alternate way to indicate return values using the format message: returnValue for messages, as you can see with isEligibleToEnroll theStudent : false.

Notice the use of stereotypes throughout the diagram. I've also used visual stereotypes on some diagrams — a stick figure for actors; the robustness diagram visual stereotypes for controller, interface, and entity objects; and a drum for the database. Stereotypes are also used on messages. For example, you see the SecurityLogon object is created in this manner actually, this message would likely be sent to the class that would then result in a return value of the created object, so I cheated a bit.

This object later destroys itself in a similar manner, presumably when the window is closed. I used a UML note in Figure 4; notes are basically free-form text that can be placed on any UML diagram, to provide a header for the diagram ,indicating its title and identifier as you may have noticed, I give unique identifiers to all artifacts that I intend to keep. Notes are depicted as a piece of paper with the top-right corner folded over. I also used a note to indicate future work that needs to be done, either during analysis or design, in this diagram-the qualifications message likely represents a series of messages sent to the student object.

Common UML practice is to anchor a note to another model element with a dashed line when appropriate, in this case the note is attached to the message. Although Figure 4 models the logic of the basic course of action for the Enroll in Seminar use case how would you go about modeling alternate courses? The easiest way to do so is to create a single sequence diagram for each alternate course, as you see depicted in Figure 5.

This diagram models only the logic of the alternate course, as you can tell by the numbering of the steps on the left-hand side of the diagram, and the header note for the diagram indicates it is an alternate course of action.

Also notice how the ID of this diagram includes that this is alternate course C, yet another modeling rule of thumb I have found useful over the years. Let's consider other sequence diagramming notation.

Figure 5 includes an initial message, Student chooses seminar , which is indicated by the filled in circle. This could easily have been indicated via a method invocation, perhaps enrollIn seminar. Figure 6 shows another way to indicate object creation — sending the new message to a class.