UML-Diagrams

                                                       P.SUDHARSAN
                                                       III BSc Computer Science
                                                       SRMVCAS

                                    

The UML diagrams are categorized into structural diagrams, behavioral diagrams, and also interaction overview diagrams. The diagrams are hierarchically classified in the following figure:



Behavioral Diagrams:

 

Behavioral diagrams portray a dynamic view of a system or the behavior of a system, which describes the functioning of the system. It includes use case diagrams, state diagrams, and activity diagrams. It defines the interaction within the system.

 

Ø  State Machine Diagram: It is a behavioral diagram. it portrays the system's behavior utilizing finite state transitions. It is also known as the State-charts diagram. It models the dynamic behavior of a class in response to external stimuli.

Notation of a State Machine Diagram

Following are the notations of a state machine diagram enlisted below:


Types of State

The UML consist of three states:

  1. Simple state: It does not constitute any substructure.
  2. Composite state: It consists of nested states (substates), such that it does not contain more than one initial state and one final state. It can be nested to any level.
  3. Submachine state: The submachine state is semantically identical to the composite state, but it can be reused.

Example of a State Machine Diagram

An example of a top-level state machine diagram showing Bank Automated Teller Machine (ATM) is given below.


Ø  Activity Diagram: It models the flow of control from one activity to the other. With the help of an activity diagram, we can model sequential and concurrent activities. It visually depicts the workflow as well as what causes an event to occur.

Components of an Activity Diagram

Activities

The categorization of behavior into one or more actions is termed as an activity. In other words, it can be said that an activity is a network of nodes that are connected by edges. The edges depict the flow of execution. It may contain action nodes, control nodes, or object nodes.

The control flow of activity is represented by control nodes and object nodes that illustrates the objects used within an activity. The activities are initiated at the initial node and are terminated at the final node.




Activity partition /swimlane

The swimlane is used to cluster all the related activities in one column or one row. It can be either vertical or horizontal. It used to add modularity to the activity diagram. It is not necessary to incorporate swimlane in the activity diagram. But it is used to add more transparency to the activity diagram.


Forks

Forks and join nodes generate the concurrent flow inside the activity. A fork node consists of one inward edge and several outward edges. It is the same as that of various decision parameters. Whenever a data is received at an inward edge, it gets copied and split crossways various outward edges. It split a single inward flow into multiple parallel flows.



Join Nodes

Join nodes are the opposite of fork nodes. A Logical AND operation is performed on all of the inward edges as it synchronizes the flow of input across one single output (outward) edge.


Pins

It is a small rectangle, which is attached to the action rectangle. It clears out all the messy and complicated thing to manage the execution flow of activities. It is an object node that precisely represents one input to or output from the action.

Notation of an Activity diagram

Activity diagram constitutes following notations:

Initial State: It depicts the initial stage or beginning of the set of actions.

Final State: It is the stage where all the control flows and object flows end.

Decision Box: It makes sure that the control flow or object flow will follow only one path.

Action Box: It represents the set of actions that are to be performed.



Example of an Activity Diagram



Ø  Use Case Diagram: It represents the functionality of a system by utilizing actors and use cases. It encapsulates the functional requirement of a system and its association with actors. It portrays the use case view of a system.

Purpose of Use Case Diagrams

The main purpose of a use case diagram is to portray the dynamic aspect of a system. It accumulates the system's requirement, which includes both internal as well as external influences. It invokes persons, use cases, and several things that invoke the actors and elements accountable for the implementation of use case diagrams. It represents how an entity from the external environment can interact with a part of the system.

Following are the purposes of a use case diagram given below:

  1. It gathers the system's needs.
  2. It depicts the external view of the system.
  3. It recognizes the internal as well as external factors that influence the system.
  4. It represents the interaction between the actors.

Example of a Use Case Diagram


Here the Web Customer actor makes use of any online shopping website to purchase online. The top-level uses are as follows; View Items, Make Purchase, Checkout, Client Register. The View Items use case is utilized by the customer who searches and view products. The Client Register use case allows the customer to register itself with the website for availing gift vouchers, coupons, or getting a private sale invitation. It is to be noted that the Checkout is an included use case, which is part of Making Purchase, and it is not available by itself

The View Items is further extended by several use cases such as; Search Items, Browse Items, View Recommended Items, Add to Shopping Cart, Add to Wish list. All of these extended use cases provide some functions to customers, which allows them to search for an item. The View Items is further extended by several use cases such as; Search Items, Browse Items, View Recommended Items, Add to Shopping Cart, Add to Wish list. All of these extended use cases provide some functions to customers, which allows them to search for an item

UML Interaction Diagram

, the interaction diagram portrays the interactions between distinct entities present in the model. It amalgamates both the activity and sequence diagrams. The communication is nothing but units of the behavior of a classifier that provides context for interactions.

A set of messages that are interchanged between the entities to achieve certain specified tasks in the system is termed as interaction. It may incorporate any feature of the classifier of which it has access. In the interaction diagram, the critical component is the messages and the lifeline.

In UML, the interaction overview diagram initiates the interaction between the objects utilizing message passing. While drawing an interaction diagram, the entire focus is to represent the relationship among different objects which are available within the system boundary and the message exchanged by them to communicate with each other.

Notation of an Interaction Diagram



Use of an Interaction Diagram

 

The interaction diagram can be used for:

  1. The sequence diagram is employed to investigate a new application.
  2. The interaction diagram explores and compares the use of the collaboration diagram sequence diagram and the timing diagram.
  3. The interaction diagram represents the interactive (dynamic) behavior of the system.
  4. The sequence diagram portrays the order of control flow from one element to the other elements inside the system, whereas the collaboration diagrams are employed to get an overview of the object architecture of the system.

UML Timing Diagram

In UML, the timing diagrams are a part of Interaction diagrams that do not incorporate similar notations as that of sequence and collaboration diagram. It consists of a graph or waveform that depicts the state of a lifeline at a specific point of time. It illustrates how conditions are altered both inside and between lifelines alongside linear time axis.

Basic concepts of a Timing Diagram

Lifeline

As the name suggests, the lifeline portrays an individual element in the interaction. It represents a single entity, which is a part of the interaction. It is represented by the classifier's name that it depicts. A lifeline can be placed within a "swimlane" or a diagram frame.


Lifelines representing instances of a System and Virus

State or Condition Timeline

The timing diagram represents the state of a classifier or attributes that are participating, or some testable conditions, which is a discrete value of the classifier.

In UML, the state or condition is continuous. It is mainly used to show the temperature and density where the entities endure a continuous state change.


Timeline showing the change in the state of virus between dormant, Propagation, Triggering, Execution

Duration Constraint

The duration constraint is a constraint of an interval, which refers to duration interval. It is used to determine if the constraint is satisfied for a duration or not. The duration constraint semantics inherits from the constraints.

The negative trace defines the violated constraints, which means the system is failed. A graphical association between duration interval and the construct, which it constrains, may represent a duration constraint.


Ice should melt into the water in 1 to 6 mins.

Time Constraint

It is an interval constraint, which refers to the time interval. Since it is a time expression, it depicts if the constraint is satisfied or not. The constraints dispense its time constraints semantics.

The negative trace defines the violated constraints, which means the system is failed. The time constraint is represented by a graphical association between the time interval and the construct which it constrains.

The graphical association is mainly represented by a small line in between a time interval and an occurrence specification.


A person should wakeup in between 5:40 am, and 6 am

Destruction Occurrence

The destruction occurrence refers to the occurrence of a message that represents the destruction of an instance is defined by a lifeline. It may subsequently destruct other objects owned by the composition of this object, such that nothing occurs after the destruction event on a given lifeline. It is represented by a cross at the end of a timeline.


Virus lifeline is terminated

Example of a Timing Diagram



Following are the seven-stage Alzheimer disease framework explained below:

  • No Impairment, Normal State
    It is the stage where the memory and cognitive abilities look normal.
  • Normal Aged Forgetfulness
    It is mostly seen in people with an age group of 65 who experience subjective complaints of cognitive and/or functional difficulties, which means they face problems in recalling the name and past 5 to 10 years of history.
  • Early Confusional, Mild Cognitive Impairment
    It causes a problem in retrieving words, planning, organizing, objects misplacing as well as forgetting fresh learning, which in turn affects the surrounding.
  • Late Confusional, Mild Alzheimer's
    In this, a person forgets the most recent events and conversations. The person remembers himself and his family, but face problems while carrying out sequential tasks such as cooking, driving, etc. Its duration is about two years,
  • Early Dementia, Moderate Alzheimer's
    In this, the person cannot manage independently. He faces difficulty in recalling the past details and contact information. It lasts for about 1.5 years.
  • Middle Dementia, Moderately Severe Alzheimer's
    It leads to insufficient awareness about current events, and the person is unable to recall the past. It causes an inability in people to take a bath and dress up independently. It lasts for about 2.5 years approximately.
  • Late or Severe Dementia, Failure to Thrive
    It is severely limited intellectual ability. In this, a person either communicates through short words or cries, which leads health to decline as it shut down the body system. Its duration is 1 to 2.5 years.

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.

Notations of a Sequence Diagram

Lifeline

An individual participant in the sequence diagram is represented by a lifeline. It is positioned at the top of the diagram.





Actor

A 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.



Activation

It 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.


Messages

The 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:

Call 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.



Note

A note is the capability of attaching several remarks to the element. It basically carries useful information for the modelers.


Sequence Fragments

  1. Sequence fragments have been introduced by UML 2.0, which makes it quite easy for the creation and maintenance of an accurate sequence diagram.
  2. It is represented by a box called a combined fragment, encloses a part of interaction inside a sequence diagram.
  3. The type of fragment is shown by a fragment operator.


Example of a Sequence Diagram

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.























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