The conceptual model of UML

The conceptual model of UML contains basic building blocks along with the rules that must be followed while building those blocks together and some general mechanisms that relate all the way through the UML.

The building blocks of UML can be defined as:

1. Things

2. Relationships

3. Diagrams

Things

Things are the most important building blocks of UML. Things can be:

• Structural

• Behavioral

• Grouping

• Annotational

Structural things

The structural things define the static part of the model. They represent physical and conceptual elements. Following are the brief descriptions of the structural things:

• Class
  Class represents set of objects having similar responsibilities.

• Interface
  Interface defines a set of operations which specify the responsibility of a class.

• Collaboration
  Collaboration defines interaction between elements.

• Use case
  Use case represents a set of actions performed by a system for a specific goal.

• Component
  Component describes physical part of a system.

• Node
  A node can be defined as a physical element that exists at run time.

Behavioral things

A behavioral thing consists of the dynamic parts of UML models. Following are the behavioral things:

• Interaction
  Interaction is defined as a behavior that consists of a group of messages exchanged among elements to accomplish a specific task.

• State machine
  State machine is useful when the state of an object in its life cycle is important. It defines the sequence of states an object goes through in response to events. Events are external factors responsible for state change.

Grouping things

Grouping things can be defined as a mechanism to group elements of a UML model together. There is only one grouping thing available:

• Package
  Package is the only one grouping thing available for gathering structural and behavioral things.

Annotational things

Annotational things can be defined as a mechanism to capture remarks, descriptions, and comments of UML model elements.

• Note
  A note is used to render comments, constraints etc of an UML element.

Relationships

Relationships are another most important building block of UML. It shows how elements are associated with each other and this association describes the functionality of an application.

There are four kinds of relationships available:

• Dependency
  Dependency is a relationship between two things in which change in one element also affects the other one.

• Association
  Association is basically a set of links that connects elements of an UML model. It also describes how many objects are taking part in that relationship.

• 
  

  Generalization
  Generalization can be defined as a relationship which connects a specialized element with a generalized element. It basically describes inheritance relationship in the world of objects.

• Realization
  Realization can be defined as a relationship in which two elements are connected. One element describes some responsibility which is not implemented and the other one implements them. This relationship exists in case of interfaces.

UML diagrams

UML diagrams are graphical representation of things in UML.
• They give static as well as dynamic view of system.

Class diagrams

Class diagrams are the most essential part of every object oriented method, including UML.
They define the fixed structure of a system. It shows a group of classes, interfaces and collaboration and their relationships.

Object diagrams

Object diagrams describe the static structure of a system at a particular time.
It shows a set of objects and their relationships. They can be used to test class diagrams for accuracy.

Use case diagrams

Use case diagrams model the functionality of system using actors and use cases and their relationships.

Sequence diagrams

Sequence diagrams describe interactions among classes in terms of an exchange of messages over time.

Collaboration diagrams

Collaboration diagrams represent interactions between objects as a series of sequenced messages.
Collaboration diagrams describe both the static structure and the dynamic behavior of a system.

State chart diagrams

State chart diagrams describe the dynamic behavior of a system in response to external stimuli.
It shows states, transitions, events and activities.
State chart diagrams are especially useful in modeling reactive objects whose states are triggered by specific events.

Activity diagrams

Activity diagrams show the dynamic nature of a system by representing the flow of control from activity to activity.
An activity represents an operation on some class in the system that results in a change in the state of the system.
Typically, activity diagrams are used to model workflow or business processes and internal operation.

Component diagrams

Component diagrams shows the organizations and dependencies among a set of components.
They describe the organization of physical software components, including source code, run-time (binary) code, and executables.

Deployment diagrams

A Deployment diagram shows the configuration of run-time processing nodes and the components that live in them.
It depict the physical resources in a system, including nodes, components, and connections.