UNIT – I

The UML is a graphical language for visualizing, specifying, constructing, and documenting the
artifacts of a software-intensive system. The UML gives you a standard way to write a system's
blueprints, covering conceptual things, such as business processes and system functions, as well as
concrete things, such as classes written in a specific programming language, database schemas,
and reusable software components.

Model
A model is a simplification of reality. A model provides the blueprints of a system. A model may be
structural, emphasizing the organization of the system, or it may be behavioral, emphasizing the
dynamics of the system.

Why do we model
We build models so that we can better understand the system we are developing.
Through modeling, we achieve four aims.
1. Models help us to visualize a system as it is or as we want it to be.
2. Models permit us to specify the structure or behavior of a system.
3. Models give us a template that guides us in constructing a system.
4. Models document the decisions we have made.

We build models of complex systems because we cannot comprehend such a system in its entirety.

Principles of Modeling
There are four basic principles of model

1. The choice of what models to create has a profound influence on how a problem is attacked
and how a solution is shaped.
2. Every model may be expressed at different levels of precision.
3. The best models are connected to reality.
4. No single model is sufficient. Every nontrivial system is best approached through a small
set of nearly independent models.
Object Oriented Modeling
In software, there are several ways to approach a model. The two most common ways are
1. Algorithmic perspective
2. Object-oriented perspective
Algorithmic Perspective
The traditional view of software development takes an algorithmic perspective.
In this approach, the main building block of all software is the procedure or function.
This view leads developers to focus on issues of control and the decomposition of larger
algorithms into smaller ones.
As requirements change and the system grows, systems built with an algorithmic focus turn
out to be very hard to maintain.
Object-oriented perspective
The contemporary view of software development takes an object-oriented perspective.
In this approach, the main building block of all software systems is the object or class.
A class is a description of a set of common objects.
Every object has identity, state, and behavior.
Object-oriented development provides the conceptual foundation for assembling systems
out of components using technology such as Java Beans or COM+.
An Overview of UML
 The Unified Modeling Language is a standard language for writing software blueprints. The
UML may be used to visualize, specify, construct, and document the artifacts of a software-
intensive system.
 The UML is appropriate for modeling systems ranging from enterprise information systems
to distributed Web-based applications and even to hard real time embedded systems. It is a
very expressive language, addressing all the views needed to develop and then deploy
such systems.
The UML is a language for
 Visualizing
 Specifying
 Constructing
 Documenting
 Visualizing The UML is more than just a bunch of graphical symbols. Rather, behind each
symbol in the UML notation is a well-defined semantics. In this manner, one developer can write
a model in the UML, and another developer, or even another tool, can interpret that model
unambiguously
 Specifying means building models that are precise, unambiguous, and complete.
 Constructing the UML is not a visual programming language, but its models can be directly
connected to a variety of programming languages
 Documenting a healthy software organization produces all sorts of artifacts in addition to raw
executable code. These artifacts include

o Requirements
o Architecture
o Design
o Source code
o Project plans
o Tests
o Prototypes
o Releases

To understand the UML, you need to form a conceptual model of the language, and this requires
learning three major elements:
1. Things
2. Relationships
3. Diagrams
Things in the UML
There are four kinds of things in the UML:
Structural things
Behavioral things
Grouping things
Annotational things
Structural things are the nouns of UML models. These are the mostly static parts of a model,
representing elements that are either conceptual or physical. In all, there are seven kinds of
structural things.
1. Classes
2. Interfaces
3. Collaborations
4. Use cases
5. Active classes
6. Components
7. Nodes
Class is a description of a set of objects that share the same attributes, operations, relationships,
and semantics. A class implements one or more interfaces. Graphically, a class is rendered as a
rectangle, usually including its name, attributes, and operations.

Interface
Interface is a collection of operations that specify a service of a class or component.
An interface therefore describes the externally visible behavior of that element.
An interface might represent the complete behavior of a class or component or only a part
of that behavior.
An interface is rendered as a circle together with its name. An interface rarely stands alone. Rather,
it is typically attached to the class or component that realizes the interface

Collaboration defines an interaction and is a society of roles and other elements that work
together to provide some cooperative behavior that's bigger than the sum of all the elements.
Therefore, collaborations have structural, as well as behavioral, dimensions. A given class might
participate in several collaborations.
Graphically, a collaboration is rendered as an ellipse with dashed lines, usually including only its
name

Usecase
 Use case is a description of set of sequence of actions that a system performs that yields an
observable result of value to a particular actor
 Use case is used to structure the behavioral things in a model.
 A use case is realized by a collaboration. Graphically, a use case is rendered as an ellipse
with solid lines, usually including only its name
Active class is just like a class except that its objects represent elements whose behavior is
concurrent with other elements. Graphically, an active class is rendered just like a class, but with
heavy lines, usually including its name, attributes, and operations

Component is a physical and replaceable part of a system that conforms to and provides the
realization of a set of interfaces. Graphically, a component is rendered as a rectangle with tabs

Node is a physical element that exists at run time and represents a computational resource,
generally having at least some memory and, often, processing capability. Graphically, a node is
rendered as a cube, usually including only its name

Behavioral Things are the dynamic parts of UML models. These are the verbs of a model,
representing behavior over time and space. In all, there are two primary kinds of behavioral things
Interaction
state machine
Interaction
Interaction is a behavior that comprises a set of messages exchanged among a set of
objects within a particular context to accomplish a specific purpose
An interaction involves a number of other elements, including messages, action sequences
and links
Graphically a message is rendered as a directed line, almost always including the name of
its operation

State Machine
State machine is a behavior that specifies the sequences of states an object or an
interaction goes through during its lifetime in response to events, together with its responses to
those events
State machine involves a number of other elements, including states, transitions, events
and activities
Graphically, a state is rendered as a rounded rectangle, usually including its name and its
substates

Grouping Things:-
1. are the organizational parts of UML models. These are the boxes into which a model can be
decomposed
2. There is one primary kind of grouping thing, namely, packages.

Package:-
 A package is a general-purpose mechanism for organizing elements into groups. Structural
things, behavioral things, and even other grouping things may be placed in a package
 Graphically, a package is rendered as a tabbed folder, usually including only its name and,
sometimes, its contents

Annotational things are the explanatory parts of UML models. These are the comments you may
apply to describe about any element in a model.

A note is simply a symbol for rendering constraints and comments attached to an element
or a collection of elements.
Graphically, a note is rendered as a rectangle with a dog-eared corner, together with a
textual or graphical comment
Relationships in the UML: There are four kinds of relationships in the UML:
1. Dependency
2. Association
3. Generalization
4. Realization
Dependency:-
Dependency is a semantic relationship between two things in which a change to one thing
may affect the semantics of the other thing
Graphically a dependency is rendered as a dashed line, possibly directed, and occasionally
including a label

Association is a structural relationship that describes a set of links, a link being a connection
among objects.
Graphically an association is rendered as a solid line, possibly directed, occasionally including a
label, and often containing other adornments, such as multiplicity and role names

Generalization is a special kind of association, representing a structural relationship between a

whole and its parts. Graphically, a generalization relationship is rendered as a solid line with a
hollow arrowhead pointing to the parent

Realization is a semantic relationship between classifiers, wherein one classifier specifies a

contract that another classifier guarantees to carry out. Graphically a realization relationship is
rendered as a cross between a generalization and a dependency relationship

Diagrams in the UML

 Diagram is the graphical presentation of a set of elements, most often rendered as a

connected graph of vertices (things) and arcs (relationships).
 In theory, a diagram may contain any combination of things and relationships.
 For this reason, the UML includes nine such diagrams:
 Class diagram
 Object diagram
 Use case diagram
 Sequence diagram
 Collaboration diagram
 Statechart diagram
 Activity diagram
 Component diagram
 Deployment diagram
Class diagram
A class diagram shows a set of classes, interfaces, and collaborations and their
relationships.
Class diagrams that include active classes address the static process view of a system.
Object diagram
 Object diagrams represent static snapshots of instances of the things found in class
diagrams
 These diagrams address the static design view or static process view of a system
 An object diagram shows a set of objects and their relationships

Use case diagram

 A use case diagram shows a set of use cases and actors and their relationships
 Use case diagrams address the static use case view of a system.
 These diagrams are especially important in organizing and modeling the behaviors of a
system.
Interaction Diagrams
Both sequence diagrams and collaboration diagrams are kinds of interaction diagrams
Interaction diagrams address the dynamic view of a system
A sequence diagram is an interaction diagram that emphasizes the time-ordering of
messages
A collaboration diagram is an interaction diagram that emphasizes the structural
organization of the objects that send and receive messages
Sequence diagrams and collaboration diagrams are isomorphic, meaning that you can take
one and transform it into the other
Statechart diagram
 A statechart diagram shows a state machine, consisting of states, transitions, events, and
activities
 Statechart diagrams address the dynamic view of a system
  They are especially important in modeling the behavior of an interface, class, or
collaboration and emphasize the event-ordered behavior of an object
Activity diagram
An activity diagram is a special kind of a statechart diagram that shows the flow from
activity to activity within a system
Activity diagrams address the dynamic view of a system
They are especially important in modeling the function of a system and emphasize the flow
of control among objects
Component diagram
 A component diagram shows the organizations and dependencies among a set of
components.
 Component diagrams address the static implementation view of a system
 They are related to class diagrams in that a component typically maps to one or more
classes, interfaces, or collaborations
Deployment diagram
 A deployment diagram shows the configuration of run-time processing nodes and the
components that live on them
 Deployment diagrams address the static deployment view of an architecture

Rules of the UML

The UML has semantic rules for
1. Names What you can call things, relationships, and diagrams
2. Scope The context that gives specific meaning to a name
3. Visibility How those names can be seen and used by others
4. Integrity How things properly and consistently relate to one another
5. Execution What it means to run or simulate a dynamic model

Models built during the development of a software-intensive system tend to evolve and may be
viewed by many stakeholders in different ways and at different times. For this reason, it is common
for the development team to not only build models that are well-formed, but also to build models
that are

1. Elided Certain elements are hidden to simplify the view

2. Incomplete Certain elements may be missing
3. Inconsistent The integrity of the model is not guaranteed

Common Mechanisms in the UML

UML is made simpler by the presence of four common mechanisms that apply consistently
throughout the language.
1. Specifications
2. Adornments
3. Common divisions
4. Extensibility mechanisms
Specification that provides a textual statement of the syntax and semantics of that building block.
The UML's specifications provide a semantic backplane that contains all the parts of all the models
of a system, each part related to one another in a consistent fashion

Adornments Most elements in the UML have a unique and direct graphical notation that provides a
visual representation of the most important aspects of the element. A class's specification may
include other details, such as whether it is abstract or the visibility of its attributes and operations.
Many of these details can be rendered as graphical or textual adornments to the class's basic
rectangular notation.

Extensibility Mechanisms
The UML's extensibility mechanisms include
1. Stereotypes
2. Tagged values
3. Constraints
Stereotype
 Stereotype extends the vocabulary of the UML, allowing you to create new kinds of building
blocks that are derived from existing ones but that are specific to your problem
 A tagged value extends the properties of a UML building block, allowing you to create new
information in that element's specification
 A constraint extends the semantics of a UML building block, allowing you to add new rules or
modify existing ones
Architecture
 A system's architecture is perhaps the most important artifact that can be used to
manage these different viewpoints and so control the iterative and incremental development of a
system throughout its life cycle.
Architecture is the set of significant decisions about

The organization of a software system

The selection of the structural elements and their interfaces by which the system is
composed
Their behavior, as specified in the collaborations among those elements
The composition of these structural and behavioral elements into progressively larger
subsystems
The architectural style that guides this organization: the static and dynamic elements
and their interfaces, their collaborations, and their composition.

Software architecture is not only concerned with structure and behavior, but also with usage,
functionality, performance, resilience, reuse, comprehensibility, economic and technology
constraints and trade-offs, and aesthetic concerns.

Vocabulary System
Assembly
Functionality Configuration Mgmt

Design View Implementation

View
Behavior Use case
view

Process View Deployment

Performance view System topology
Scalability distribution delivery
Throughput installation

Modeling a System's Architecture

Use case view

The use case view of a system encompasses the use cases that describe the behavior of
the system as seen by its end users, analysts, and testers.
With the UML, the static aspects of this view are captured in use case diagrams
The dynamic aspects of this view are captured in interaction diagrams, state chart
diagrams, and activity diagrams.
Design View
 The design view of a system encompasses the classes, interfaces, and collaborations that form
the vocabulary of the problem and its solution.
 This view primarily supports the functional requirements of the system, meaning the services
that the system should provide to its end users.
Process View
 The process view of a system encompasses the threads and processes that form the system's
concurrency and synchronization mechanisms.
 This view primarily addresses the performance, scalability, and throughput of the system
Implementation View
The implementation view of a system encompasses the components and files that are
used to assemble and release the physical system.
This view primarily addresses the configuration management of the system's releases,
made up of somewhat independent components and files that can be assembled in various ways to
produce a running system.
Deployment Diagram
The deployment view of a system encompasses the nodes that form the system's
hardware topology on which the system executes.
This view primarily addresses the distribution, delivery, and installation of the parts that
make up the physical system.
Software Development Life Cycle:

The UML is largely process-independent, meaning that it is not tied to any particular
software development life cycle. However, to get the most benefit from the UML, you
should consider a process that is

 Use case driven

 Architecture-centric
 Iterative and incremental

Use case driven means that use cases are used as a primary artifact for establishing the
desired behavior of the system, for verifying and validating the system's architecture, for
testing, and for communicating among the stakeholders of the project.

Architecture-centric means that a system's architecture is used as a primary artifact for

conceptualizing, constructing, managing, and evolving the system under development.

An iterative process is one that involves managing a stream of executable releases. An

incremental process is one that involves the continuous integration of the system's
architecture to produce these releases, with each new release embodying incremental
improvements over the other. Together, an iterative and incremental process is risk-
driven, meaning that each new release is focused on attacking and reducing the most
significant risks to the success of the project.

This use case driven, architecture-centric, and iterative/incremental process can be

broken into phases. A phase is the span of time between two major milestones of the
process, when a well-defined set of objectives are met, artifacts are completed, and
decisions are made whether to move into the next phase. As Figure shows, there are four
phases in the software development life cycle: inception, elaboration, construction, and
transition. In the diagram, workflows are plotted against these phases, showing their
varying degrees of focus over time.

Inception is the first phase of the process, when the seed idea for the development is
brought up to the point of being—at least internally—sufficiently well-founded to
warrant entering into the elaboration phase.

Elaboration is the second phase of the process, when the product vision and its
architecture are defined. In this phase, the system's requirements are articulated,
prioritized, and base lined. A system's requirements may range from general vision
statements to precise evaluation criteria, each specifying particular functional or
nonfunctional behavior and each providing a basis for testing.

Construction is the third phase of the process, when the software is brought from an
executable architectural baseline to being ready to be transitioned to the user community.
Here also, the system's requirements and especially its evaluation criteria are constantly
reexamined against the business needs of the project, and resources are allocated as
appropriate to actively attack risks to the project.

Transition is the fourth phase of the process, when the software is turned into the hands
of the user community. Rarely does the software development process end here, for even
during this phase, the system is continuously improved, bugs are eradicated, and features
that didn't make an earlier release are added.

One element that distinguishes this process and that cuts across all four phases is an
iteration. An iteration is a distinct set of activities, with a base lined plan and evaluation
criteria that result in a release, either internal or external. This means that the software
development life cycle can be characterized as involving a continuous stream of
executable releases of the system's architecture. It is this emphasis on architecture as an
important artifact that drives the UML to focus on modeling the different views of a
system's architecture.

Software Development Life Cycle