Lifeline In Sequence Diagram

Lifeline In Sequence Diagram

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Lifeline In Sequence Diagram
Lifeline In A Sequence Diagram
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. In UML, the lifeline is represented by a vertical bar, whereas the message flow is represented by a vertical dotted line that extends across the bottom of the page. It incorporates the iterations as well as branching.
Purpose of a Sequence DiagramTo model high-level interaction among active objects within a system.
To model interaction among objects inside a collaboration realizing a use case.
It either models generic interactions or some certain instances of interaction.
Notations of a Sequence DiagramLifelineAn individual participant in the sequence diagram is represented by a lifeline. It is positioned at the top of the diagram. 
A lifeline notation with an actor element symbol is used when the particular sequence diagram is owned by a use case. A lifeline with an entity element represents system data. For example, in a customer service application, the Customer entity would manage all data related to a customer. Sequence diagram describes an interaction by focusing on the sequence of messages that are exchanged, along with their corresponding occurrence specifications on the lifelines. In a sequence diagram, a lifeline is represented by a vertical bar. A message flow between two or more objects is represented using a vertical dotted line which extends across the bottom of the page. In a sequence diagram, different types of messages and operators are used which are described above.
ActorA role played by an entity that interacts with the subject is called as an actor. It is out of the scope of the system. It represents the role, which involves human users and external hardware or subjects. An actor may or may not represent a physical entity, but it purely depicts the role of an entity. Several distinct roles can be played by an actor or vice versa.

ActivationIt is represented by a thin rectangle on the lifeline. It describes that time period in which an operation is performed by an element, such that the top and the bottom of the rectangle is associated with the initiation and the completion time, each respectively.
MessagesThe messages depict the interaction between the objects and are represented by arrows. They are in the sequential order on the lifeline. The core of the sequence diagram is formed by messages and lifelines.
Following are types of messages enlisted below:
Sequence Diagram Tutorial With ExampleCall Message: It defines a particular communication between the lifelines of an interaction, which represents that the target lifeline has invoked an operation.
Return Message: It defines a particular communication between the lifelines of interaction that represent the flow of information from the receiver of the corresponding caller message.
Self Message: It describes a communication, particularly between the lifelines of an interaction that represents a message of the same lifeline, has been invoked.
Recursive Message: A self message sent for recursive purpose is called a recursive message. In other words, it can be said that the recursive message is a special case of the self message as it represents the recursive calls.
Create Message: It describes a communication, particularly between the lifelines of an interaction describing that the target (lifeline) has been instantiated.
Destroy Message: It describes a communication, particularly between the lifelines of an interaction that depicts a request to destroy the lifecycle of the target.
Duration Message: It describes a communication particularly between the lifelines of an interaction, which portrays the time passage of the message while modeling a system.
NoteA note is the capability of attaching several remarks to the element. It basically carries useful information for the modelers.
Sequence FragmentsSequence fragments have been introduced by UML 2.0, which makes it quite easy for the creation and maintenance of an accurate sequence diagram.
It is represented by a box called a combined fragment, encloses a part of interaction inside a sequence diagram. 
The type of fragment is shown by a fragment operator. 
Types of fragmentsFollowing are the types of fragments enlisted below;
OperatorFragment Type
altAlternative multiple fragments: The only fragment for which the condition is true, will execute.
optOptional: If the supplied condition is true, only then the fragments will execute. It is similar to alt with only one trace.
parParallel: Parallel executes fragments.
loopLoop: Fragments are run multiple times, and the basis of interaction is shown by the guard.
regionCritical region: Only one thread can execute a fragment at once.
negNegative: A worthless communication is shown by the fragment.
refReference: An interaction portrayed in another diagram. In this, a frame is drawn so as to cover the lifelines involved in the communication. The parameter and return value can be explained.
sdSequence Diagram: It is used to surround the whole sequence diagram.
Example of a Sequence DiagramAn example of a high-level sequence diagram for online bookshop is given below.
Any online customer can search for a book catalog, view a description of a particular book, add a book to its shopping cart, and do checkout.
Benefits of a Sequence DiagramIt explores the real-time application.
It depicts the message flow between the different objects.
It has easy maintenance.
It is easy to generate.
Implement both forward and reverse engineering.
It can easily update as per the new change in the system. 
The drawback of a Sequence DiagramSequence Diagram PdfIn the case of too many lifelines, the sequence diagram can get more complex.
The incorrect result may be produced, if the order of the flow of messages changes. 
Since each sequence needs distinct notations for its representation, it may make the diagram more complex.
The type of sequence is decided by the type of message.
Lifeline In Sequence DiagramNext TopicUML Collaboration Diagram
Lifeline In A Sequence Diagram

Operator	Fragment Type
alt	Alternative multiple fragments: The only fragment for which the condition is true, will execute.
opt	Optional: If the supplied condition is true, only then the fragments will execute. It is similar to alt with only one trace.
par	Parallel: Parallel executes fragments.
loop	Loop: Fragments are run multiple times, and the basis of interaction is shown by the guard.
region	Critical region: Only one thread can execute a fragment at once.
neg	Negative: A worthless communication is shown by the fragment.
ref	Reference: An interaction portrayed in another diagram. In this, a frame is drawn so as to cover the lifelines involved in the communication. The parameter and return value can be explained.
sd	Sequence Diagram: It is used to surround the whole sequence diagram.