a. Activity diagram: captures the process flow. They are used for functional modeling.
b. Sequence diagram: the track the interaction between the objects. They are used for dynamic modeling.
The following are the difference between Activity and Sequence Diagrams:
A sequence diagram shows the way of processes execute in a sequence. For example, the order of operations and the parameters.
► An activity diagram depicts the operational workflows.
► A sequence diagram is focused to represent interactions between different objects.
► Activity diagram shows the actions for various objects.
Use case diagram is a subset of various behaviour diagrams. Use case diagrams are used to provide concrete examples of the elements which are supposed to implement. It is used to analyze objects.
The following are the elements of the use case diagrams:
Actors: An actor is one of the entities who perform certain actions. These roles are the actual business roles of the users in given system. An actor interacts with a use case of the system. For example, for a banking system, a customer is one of the actors.
Use Case: A use case is a use case diagram of UML represents a business functionality that is distinct. The use case should list the discrete business functionality that is specified in the problem statement. Every business functionality is a potential use case.
System boundary: A system boundary defines the scope of the system. The systems that use cases also need to be defined in the limits of the system. The system boundary is shown as a rectangle that spans all use cases of the system.
► Activities: An activity indicates an action that performed in the system.
► Transitions: Transitions are represented by open arrow heads. Transitions are used to indicate the flow among elements in the diagram.
► Decision Points: The logical branching is depicted by the decision points.
► States: A state is shown in a rounded rectangle. States are indicated to mention the mile stones of processing in the activity diagrams.
► Object: The interaction between objects takes place in a system. An object is depicted by a rectangle with the name of the object, preceded by a colon and underline.
► Relation/Association: Association among objects is linked by connecting them. The cardinality can be depicted by placing qualifiers on either ends.
► Messages: An arrow that commencing from one object to the destination object. This depicts the interaction between objects. The sequence or order of the interaction is depicted by the number.
a. Initial State: The first or the default state the object is in. It is denoted by a solid circle.
b. State: All the states an object can go in are mentioned in this. It is represented by a rectangle with rounded edges.
c. Transitions: depicted by arrow from the source state to destination state.
d. Final State: Depicts the end of the. It is shown by a bull's eye symbol.
► Initial State: This state shows the first activity of the flow.
► State: A state represents the state of an object at a particular given point of time.
► Transition: The transition from one state to another state of objects is represented by an arrow.
► Event and Action: A trigger that causes a transition to occur.
► Signal: When a message or a trigger caused by an event to a state, which causes a transition, this message is called as a signal.
► Final State: The state diagram ends with a diagram that depicts a bull's eye is known as Final State.
► Nodes: A node represents any hardware component. The configuration of hardware is represented by attributes of nodes.
► Components: A component represents software. Each component straightly represents a class or object that in turn represents methods.
► Dependencies: The reliability of one component with that of another is depicted by dependencies.
► Links: To tie up tow nodes, the links are utilized. The links are implemented by using nodes and their associations.
► Actor: Actor represents an external user / end user who interact with the system.
► Object: Object is represented by one of components of the system.
► Unit: A unit is a subsystem, or a sub component or other entity within the system.
► Separator: Separator represents a boundary among sub systems, components or units.
► Group: Represents different header elements in the subsystem.
A component diagram is particularly useful with teams of larger size. UML components are great to perform architectural landscape for a specific system. The component diagram allows to model high level software components and interfaces to those components. The sub team's effort is very less, once the interfaces are perfectly designed and accepted by the team members.