UML

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Software Engineering
Topic:
UML
Unified Modelling Language

Definition
Ϟ UML is a standard language for specifying, visualizing,
constructing and documenting the artifacts of software
systems.
Ϟ UML is different from the other programming languages
like Java, C++ but tools can be used to generate code in
various languages using UML diagrams.
Ϟ UML is a pictorial language used to make software blue
prints.

Goals of UML
ϞA picture is worth a thousand words, this absolutely fits while
discussing about UML.
ϞUML diagrams are not only for developers but also for
business users, common people and anybody interested to
understand the system. So it must be clear that UML is not a
development method rather it accompanies with processes to
make a successful system.
ϞThe goal of UML can be defined as a simple modelling
mechanism to model all possible practical systems in today’s
complex environment.

Building Blocks
This chapter describes all the UML building blocks. It can be defined as:
ϞThings
ϞRelationships
ϞDiagrams
1. Things
Things are the most important building blocks of UML. Things can be:
•Structural
•Behavioral
•Grouping
•Annotational

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

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.

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 is the only one Annotational thing available.
Note:
A note is used to render comments, constraints etc of an UML
element.

2. Relationship
Relationship is 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.

3. Diagrams
UML diagrams are the ultimate output of the entire discussion. All
the elements, relationships are used to make a complete UML
diagram and the diagram represents a system.
UML includes the following nine diagrams
Structural Diagrams:
1. Class diagram
2. Object diagram
3. Component diagram
4. Deployment diagram
Behavioral Diagrams:
5. Use case diagram
6. Sequence diagram
7. Collaboration diagram
8. State diagram
9. Activity diagram
.

Class Diagram
Class diagrams are widely used to describe the types of objects
in a system and their relationships. Class diagram consists of
classes, interfaces, associations and collaboration.
Classes are composed of three things: a name, attributes, and
operations. Below is an example of a class.
.

Class diagrams also display relationships such as containment,
inheritance, associations and others.
Another common relationship in class diagrams is a generalization.
A generalization is used when two classes are similar, but have
some differences. Look at the generalization below:

When to Use: Class Diagrams
Class diagrams are used in nearly all Object Oriented software
designs. Use them to describe the Classes of the system and
their relationships to each other.
How to Draw: Class Diagrams
Class diagrams are some of the most difficult UML diagrams to
draw. To draw detailed and useful diagrams a person would
have to study UML and Object Oriented principles for a long
time. Therefore, this page will give a very high level overview of
the process.

Object Diagram
Object diagrams can be described as an instance of class diagram.
So these diagrams are more close to real life scenarios where we
implement a system.
Object diagrams are a set of objects and their relationships just like
class diagrams and also represent the static view of the system.
The usage of object diagrams is similar to class diagrams but they
are used to build prototype of a system from practical perspective.

Component Diagram
Component diagrams represent a set of components and
their relationships. These components consist of classes,
interfaces or collaborations.
So Component diagrams represent the implementation
view of a system.
During design phase software artifacts (classes, interfaces
etc) of a system are arranged in different groups
depending upon their relationship. Now these groups are
known as components.
Finally, component diagrams are used to visualize the
implementation.

Deployment Diagram
Deployment diagrams are a set of nodes and their
relationships. These nodes are physical entities where the
components are deployed.
Deployment diagrams are used for visualizing deployment
view of a system. This is generally used by the deployment
team.
Note: If the above descriptions and usages are observed
carefully then it is very clear that all the diagrams are
having some relationship with one another. Component
diagrams are dependent upon the classes, interfaces etc
which are part of class/object diagram. Again the
deployment diagram is dependent upon the components
which are used to make a component diagrams.

Use Case Diagrams
A use case is a set of scenarios that describing an interaction
between a user and a system. A use case diagram displays the
relationship among actors and use cases. The two main
components of a use case diagram are use cases and actors.
An actor is represents a user or another system that will interact with
the system you are modeling. A use case is an external view of the
system that represents some action the user might perform in order
to complete a task.

When to Use: Use Cases Diagrams
Use cases are used in almost every project. These are helpful in
exposing requirements and planning the project. During the initial
stage of a project most use cases should be defined, but as the
project continues more might become visible.
How to Draw: Use Cases Diagrams
Use cases are a relatively easy UML diagram to draw, but this is a
very simplified example. Start by listing a sequence of steps a user
might take in order to complete an action.

1. Browse catalog and select items.
2. Call sales representative.
3. Supply shipping information.
4. Supply payment information.
5. Receive conformation number from salesperson.
These steps would generate this simple use case diagram:

Sequence Diagram
A sequence diagram is an interaction diagram. From the
name it is clear that the diagram deals with some
sequences, which are the sequence of messages flowing
from one object to another.
Interaction among the components of a system is very
important from implementation and execution perspective.
So Sequence diagram is used to visualize the sequence of
calls in a system to perform a specific functionality.

Collaboration Diagram
Collaboration diagram is another form of interaction
diagram. It represents the structural organization of a
system and the messages sent/received. Structural
organization consists of objects and links.
The purpose of collaboration diagram is similar to sequence
diagram. But the specific purpose of collaboration diagram
is to visualize the organization of objects and their
interaction.

State Diagram
State diagrams are used to describe the behavior of a system. State
diagrams describe all of the possible states of an object as events
occur. Each diagram usually represents objects of a single class
and track the different states of its objects through the system.
When to Use: State Diagrams
Use state diagrams to demonstrate the behavior of an object
through many use cases of the system. Only use state diagrams for
classes where it is necessary to understand the behavior of the
object through the entire system. Not all classes will require a state
diagram and state diagrams are not useful for describing the
collaboration of all objects in a use case.

How to Draw: State Diagrams
State diagrams have very few elements. The basic elements are
rounded boxes representing the state of the object and arrows
indicting the transition to the next state. The activity section of the
state symbol depicts what activities the object will be doing while it
is in that state.
All state diagrams being with an initial state of the object. This is
the state of the object when it is created. After the initial state the
object begins changing states. Conditions based on the activities
can determine what the next state the object transitions to.

Activity Diagrams
Activity diagrams describe the workflow behavior of a system. Activity
diagrams are similar to state diagrams because activities are the
state of doing something. The diagrams describe the state of
activities by showing the sequence of activities performed. Activity
diagrams can show activities that are conditional or parallel.
When to Use: Activity Diagrams
Activity diagrams should be used in conjunction with other modeling
techniques such as interaction diagrams and state diagrams. The
main reason to use activity diagrams is to model the workflow behind
the system being designed. Activity Diagrams are also useful for:
analyzing a use case by describing what actions need to take place
and when they should occur; describing a complicated sequential
algorithm; and modeling applications with parallel processes.

How to Draw: Activity Diagrams
Activity diagrams show the flow of activities through the system.
Diagrams are read from top to bottom and have branches and forks
to describe conditions and parallel activities. A fork is used when
multiple activities are occurring at the same time.
The diagram below shows a fork after activity1. This indicates that
both activity2 and activity3 are occurring at the same time. After
activity2 there is a branch. The branch describes what activities will
take place based on a set of conditions. All branches at some point
are followed by a merge to indicate the end of the conditional
behavior started by that branch. After the merge all of the parallel
activities must be combined by a join before transitioning into the
final activity state

That’s it 

UML

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