A sequence diagram _____.


UML Sequence Diagrams are interactivity diagrams that detail how operations are carried out. They capture the interactivity in between objects in the context of a teamwork. Sequence Diagrams are time focus and they display the order of the interactivity visually by making use of the vertical axis of the diagram to reexisting time what messages are sent and once.

You watching: A sequence diagram _____.


Sequence Diagrams captures:

the interaction that takes location in a cooperation that either realizes a usage situation or an procedure (instance diagrams or generic diagrams)high-level interactions between user of the mechanism and also the device, in between the mechanism and also various other systems, or between subsystems (sometimes well-known as system sequence diagrams)
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Purpose of Sequence Diagram

Model high-level interaction between active objects in a systemModel the interaction in between object instances within a cooperation that realizes a use caseModel the interaction between objects within a teamwork that realizes an operationEither version generic interactions (mirroring all possible paths via the interaction) or specific instances of a interactivity (reflecting simply one course through the interaction)

Sequence Diagrams at a Glance

Sequence Diagrams show elements as they interact over time and also they are arranged according to object (horizontally) and also time (vertically):

Object DimensionThe horizontal axis mirrors the facets that are connected in the interactionConventionally, the objects associated in the operation are listed from left to right according to once they take part in the message sequence. However before, the elements on the horizontal axis might appear in any orderTime DimensionThe vertical axis represents time proceedings (or progressing) dvery own the page.

Note that:

Time in a sequence diagram is all a about ordering, not duration. The vertical area in an interaction diagram is not pertinent for the duration of the interaction.

Sequence Diagram Example: Hotel System

Sequence Diagram is an interaction diagram that details how operations are lugged out -- what messeras are sent out and also when. Sequence diagrams are arranged according to time. The time progresses as you go dvery own the web page. The objects involved in the procedure are provided from left to best according to once they take component in the message sequence.

Below is a sequence diagram for making a hotel reservation. The object initiating the sequence of messperiods is a Reservation window.


Note That: Class and object diagrams are static version views. Interactivity diagrams are dynamic. They explain just how objects collaborate.

Sequence Diagram Notation

Notation DescriptionVisual Representation


a form of function played by an entity that interacts through the subject (e.g., by exchanging signals and data)external to the topic (i.e., in the feeling that an instance of an actor is not a component of the instance of its corresponding subject).represent duties played by huguy users, outside hardware, or various other subjects.

Note that:

An actor does not necessarily reexisting a certain physical entity however just a certain duty of some entityA person might play the function of a number of different actors and also, conversely, a offered actor may be played by multiple different perboy.


A lifeline represents an individual participant in the Interaction.


A thin rectangle on a lifeline) represents the period in the time of which an facet is perdeveloping an procedure.The peak and the bottom of the of the rectangle are aligned with the initiation and also the completion time respectively

Call Message

A message defines a specific interaction between Lifelines of an Interactivity.Call message is a kind of message that represents an invocation of procedure of tarobtain lifeline.

Return Message

A message specifies a details communication in between Lifelines of an Interaction.Rerotate message is a type of message that represents the pass of indevelopment back to the caller of a corresponded former message.

Self Message

A message defines a details interaction between Lifelines of an Interaction.Self message is a type of message that represents the invocation of message of the same lifeline.

Recursive Message

A message defines a details interaction in between Lifelines of an Interactivity.Recursive message is a sort of message that represents the invocation of message of the exact same lifeline. It"s targain points to an activation on optimal of the activation where the message was invoked from.

Create Message

A message defines a specific communication in between Lifelines of an Interactivity.Create message is a kind of message that represents the instantiation of (target) lifeline.

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Destroy Message

A message specifies a particular communication in between Lifelines of an Interaction.Destroy message is a type of message that represents the research of destroying the lifecycle of taracquire lifeline.

Duration Message

A message defines a details communication between Lifelines of an Interaction.Duration message mirrors the distance in between two time instants for a message invocation.


A note (comment) gives the capability to affix miscellaneous remarks to elements. A comment carries no semantic pressure, yet might contain indevelopment that is beneficial to a modeler.


Blog post and Focus of Control

An Event is any point in an interactivity wright here something occurs.Focus of control: also dubbed execution incident, an execution occurrenceIt mirrors as tall, thin rectangle on a lifeline)It represents the duration in the time of which an element is percreating an operation. The top and also the bottom of the rectangle are aligned with the initiation and the completion time respectively.

Sequence Fragments

A sequence fragment is stood for as a box, called an unified fragment, which encloses a portion of the interactions within a sequence diagramThe fragment operator (in the top left cornet) suggests the kind of fragmentFragment types: ref, assert, loop, break, alt, opt, neg
OperatorFragment Type
altAlteraboriginal multiple fragments: only the one whose condition is true will certainly execute.
optOptional: the fragment executes only if the supplied condition is true. Equivalent to an alt only through one trace.
parParallel: each fragment is run in parallel.
loopLoop: the fragment might execute multiple times, and the guard shows the basis of iteration.
regionCritical region: the fragment have the right to have just one threview executing it at once.
negNegative: the fragment reflects an invalid interactivity.
refReference: describes an interactivity identified on one more diagram. The frame is drawn to cover the lifelines affiliated in the interaction. You can specify parameters and also a rerevolve worth.
sdSequence diagram: provided to surround a whole sequence diagram.

Note That:

It is possible to incorporate frames in order to capture, e.g., loops or branches.

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Incorporated fragment keywords: alt, opt, break, par, seq, strict, neg, critical, overlook, consider, assert and loop.Constraints are commonly supplied to present timing constraints on messperiods. They can use to the timing of one message or intervals in between messages.Integrated Fragment Example

Sequence Diagram for Modeling Use Case Scenarios

User requirements are captured as usage situations that are polished right into scenarios. A usage situation is a collection of interactions between exterior actors and a device. In UML, a usage instance is:

"the specification of a sequence of actions, including variants, that a system (or entity) deserve to perform, interacting via actors of the device."

A scenario is one route or circulation with a usage situation that describes a sequence of events that occurs in the time of one specific execution of a mechanism which is regularly represented by a sequence diagram.


Sequence Diagram - Model prior to Code

Sequence diagrams deserve to be somewhat close to the code level, so why not just code up that algorithm rather than illustration it as a sequence diagram?

A good sequence diagram is still a little above the level of the real codeSequence diagrams are language neutralNon-coders have the right to execute sequence diagramsEasier to execute sequence diagrams as a team