SOA Unit I

Service Oriented Architecture

UNIT – I

By
Dileep Kumar G
Lecturer / School of Computing
Adama Science & Technology University

01/20/13 Unit 1

Roots of SOA
(comparing SOA to past architectures)

What is architecture?
 IT departments started to recognize the need for a
standardized definition of a baseline application that
could act as a template for all others.
 This definition was abstract in nature, but specifically
explained the technology, boundaries, rules, limitations,
and design characteristics that apply to all solutions
based on this template.
 This was the birth of the application architecture.

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Types of Architectures
1. Application architecture
2. Enterprise architecture
3. Service-oriented architecture

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Application architecture
Application architecture is to an application development
team what a blueprint is to a team of construction
workers.
Different organizations document different levels of
application architecture.
Some keep it high-level, providing abstract physical and
logical representations of the technical blueprint. Others
include more detail, such as common data models,
communication flow diagrams, application-wide security
requirements, and aspects of infrastructure.

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Application architecture……..
It is not uncommon for an organization to have several
application architectures.
A single architecture document typically represents a
distinct solution environment. For example, an
organization that houses both .NET and J2EE solutions
would very likely have separate application architecture
specifications for each.
A key part of any application-level architecture is that it
reflects immediate solution requirements, as well as long-
term, strategic IT goals.

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Enterprise architecture
 In larger IT environments, the need to control and direct IT
infrastructure is critical.

 When numerous, disparate application architectures co-exist and
sometimes even integrate, the demands on the underlying hosting
platforms can be complex and onerous.

 Therefore, it is common for a master specification to be created,
providing a high-level overview of all forms of heterogeneity that exist
within an enterprise, as well as a definition of the supporting
infrastructure.

 Continuing our previous analogy, an enterprise architecture
specification is to an organization what an urban plan is to a city.
Therefore, the relationship between an urban plan and the blueprint of
a building are comparable to that of enterprise and application
architecture specifications.

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Enterprise architecture…
Typically, changes to enterprise architectures directly
affect application architectures, which is why architecture
specifications often are maintained by the same group of
individuals.

Further ,enterprise architectures often contain a long-
term vision of how the organization plans to evolve its
technology and environments.

For example, the goal of phasing out an outdated
technology platform may be established in this
specification.
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Service-Oriented Architecture
Service-oriented architecture spans both enterprise and
application architecture domains.

The benefit potential offered by SOA can only be truly
realized when applied across multiple solution
environments.

This is where the investment in building reusable and
interoperable services based on a vendor-neutral
communications platform can fully be leveraged. This
does not mean that the entire enterprise must become
service-oriented.

SOA belongs in those areas that have the most to gain
from the features and characteristics it introduces.
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Service-Oriented Architecture….
Note that the term "SOA" does not necessarily imply
a particular architectural scope.

 An SOA can refer to an application architecture or the
approach used to standardize technical architecture across
the enterprise.

Because of the composable nature of SOA (meaning that
individual application-level architectures can be
comprised of different extensions and technologies), it is
absolutely possible for an organization to have more than
one SOA.
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Characteristics of SOA
The following primary characteristics:
1. Contemporary SOA is at the core of the service-
oriented computing platform.
2. Contemporary SOA increases quality of service.
3. Contemporary SOA is fundamentally autonomous.
4. Contemporary SOA is based on open standards.
5. Contemporary SOA supports vendor diversity.
6. Contemporary SOA fosters intrinsic interoperability.
7. Contemporary SOA promotes discovery.
8. Contemporary SOA promotes federation.
9. Contemporary SOA promotes architectural
composability.
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10. Contemporary SOA fosters inherent reusability.
11. Contemporary SOA emphasizes extensibility.
12. Contemporary SOA supports a service-oriented
business modeling paradigm.
13. Contemporary SOA implements layers of abstraction.
14. Contemporary SOA promotes loose coupling
throughout the enterprise.
15. Contemporary SOA promotes organizational agility.
16. Contemporary SOA is a building block.
17. Contemporary SOA is an evolution.
18. Contemporary SOA is still maturing.
19. Contemporary SOA is an achievable ideal.

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1. Contemporary SOA is at the core of the
service-oriented computing platform.
• An application computing platform consisting of Web
services technology and service-orientation principles.
• Represents an architecture that promotes service-
orientation through the use of Web services.

1. Contemporary SOA increases quality of
service
• There is a need to bring SOA to a point where it can
implement enterprise-level functionality as safely and
reliably as the more established distributed
architectures already do.

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Characteristics of SOA Cont…
 This relates to common quality of service requirements, such
as:
 The ability for tasks to be carried out in a secure manner, protecting the
contents of a message, as well as access to individual services.
 Allowing tasks to be carried out reliably so that message delivery or
notification of failed delivery can be guaranteed.
 Performance requirements to ensure that the overhead imposed by
SOAP message and XML content processing does not inhibit the
execution of a task.
 Transactional capabilities to protect the integrity of specific business
tasks with a guarantee that should the task fail, exception logic is
executed.

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Characteristics of SOA Cont…
3. Contemporary SOA is fundamentally autonomous
 Requires that individual services be as independent and self-contained
as possible with respect to the control they maintain over their
underlying logic.
 This is further realized through message-level autonomy where
messages passed between services are sufficiently intelligence-heavy
that they can control the manner in which they are processed by
recipient services.
 SOA builds upon and expands this principle by promoting the concept
of autonomy throughout solution environments and the enterprise.
4. Contemporary SOA is based on open standards
 Significant characteristic of Web services is the fact that data exchange
is governed by open standards.
 After a message is sent from one Web service to another it travels via
a set of protocols that is globally standardized and accepted. i.e. the
message itself is standardized, both in format and in how it represents
its payload.

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Figure: Standard open technologies are used within and outside of solution boundaries.

5. Contemporary SOA supports vendor diversity

The open communications framework has significant
implications for bridging much of the heterogeneity within (and
between) corporations, but it also allows organizations to
choose best-of-breed environments for specific applications.

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 For example, regardless of how proprietary a development
environment is, as long as it supports the creation of standard Web
services, it can be used to create a non-proprietary service interface
layer, opening up interoperability opportunities with other, service-
capable applications (shown in Figure)

Figure : Disparate technology platforms do not prevent service-oriented solutions
from interoperating

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 Organizations can certainly continue building solutions with
existing development tools and server products.
 The choice to explore the offerings of new vendors is always there.
This option is made possible by the open technology provided by
the Web services framework and is made more attainable through
the standardization and principles introduced by SOA.
6. Contemporary SOA promotes discovery
 The first generation of Web services standards included UDDI, few
of the early implementations actually used service registries as part
of their environments.
 This may have to do with the fact that not enough Web services
were actually built to warrant a registry.

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 However, another reason is that the concept of service discovery
was simply not designed into the architecture. When utilized
within traditional distributed architectures, Web services were
more often employed to facilitate point-to-point solutions.
Therefore, discovery was not a common concern.
 SOA supports and encourages the advertisement and discovery of
services throughout the enterprise and beyond.
 A serious SOA will likely rely on some form of service registry or
directory to manage service descriptions

Figure : Registries enable a mechanism for the discovery of
services.

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7. Contemporary SOA fosters intrinsic
interoperability
 An application actually has immediate integration
requirements.
Design principles can be applied to outfit services with
characteristics that naturally promote interoperability.
When building an SOA application from the ground up,
services with intrinsic interoperability become potential
integration endpoints (Figure).

Figure: Intrinsically interoperable services enable unforeseen integration opportunities
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When properly standardized, this leads to service-
oriented integration architectures wherein solutions
themselves achieve a level of intrinsic interoperability.
Fostering this characteristic can significantly alleviate
the cost and effort of fulfilling future cross-application
integration requirements.
8. Contemporary SOA promotes federation
One of the most attractive aspects of the architecture is
its ability to introduce unity across previously non-
federated environments.

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While Web services enable federation, SOA promotes
this cause by establishing and standardizing the ability
to encapsulate legacy and non-legacy application logic
and by exposing it via a common, open, and
standardized communications framework (also
supported by an extensive adapter technology
marketplace).
The incorporation of SOA with previous platforms can
lead to a variety of hybrid solutions.
However, the key aspect is that the communication
channels achieved by this form of service-oriented
integrations are all uniform and standardized (Figure).

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Figure : Services enable standardized federation of disparate legacy systems

9. Contemporary SOA promotes architectural
composability
Composability is a deep-rooted characteristic of SOA
that can be realized on different levels.
For example, by fostering the development and
evolution of composable services, SOA supports the
automation of flexible and highly adaptive business
processes. As previously mentioned, services exist as
independent units of logic.
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A business process can therefore be broken down into a
series of services, each responsible for executing a
portion of the process.
A broader example of composability is represented by
the second-generation Web services framework that is
evolving out of the release of the numerous WS-*
specifications.
The modular nature of these specifications allows an
SOA to be composed of only the functional building
blocks it requires.

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What provides this flexibility is the fact that second-
generation Web services specifications are being
designed specifically to leverage the SOAP messaging
model.
Individual specifications consist of modular extensions
that provide one or more specific features.
As the offering of WS-* extensions supported by a given
vendor platform grows, the flexibility to compose
allows you to continue building solutions that only
implement the features you actually need (Figure).

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Figure :Different solutions can be composed of different extensions and can continue to
interoperate as long as they support the common extensions required.

In other words, the WS-* platform allows for the
creation of streamlined and optimized service-oriented
architectures, applications, services, and even messages.

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10. Contemporary SOA fosters inherent
reusability
SOA establishes an environment that promotes reuse
on many levels.
For example, services designed according to service-
orientation principles are encouraged to promote reuse,
even if no immediate reuse requirements exist.
Collections of services that form service compositions
can themselves be reused by larger compositions.

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The emphasis placed by SOA on the creation of services
that are agnostic to both the business processes and the
automation solutions that utilize them leads to an
environment in which reuse is naturally realized as a
side benefit to delivering services for a given project.
Thus, inherent reuse can be fostered when building
service-oriented solutions (Figure ).

Figure : Inherent reuse accommodates unforeseen reuse opportunities.

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11. Contemporary SOA emphasizes extensibility
When expressing encapsulated functionality through a
service description, SOA encourages you to think
beyond immediate, point-to-point communication
requirements.
When service logic is properly partitioned via an
appropriate level of interface granularity, the scope of
functionality offered by a service can sometimes be
extended without breaking the established interface
(Figure ).

Figure :Extensible services can expand functionality with minimal impact.

01/20/13 Unit 1

Extensibility is also a characteristic that is promoted
throughout SOA as a whole.
Extending entire solutions can be accomplished by
adding services or by merging with other service-
oriented applications (which also, effectively, "adds
services").
Because the loosely coupled relationship fostered among
all services minimizes inter-service dependencies,
extending logic can be achieved with significantly less
impact.
Contemporary SOA represents an open, extensible,
federated, composable architecture that promotes
service-orientation and is comprised of autonomous,
QoS-capable, vendor diverse, interoperable,
discoverable, and potentially reusable services,
01/20/13 implemented 1Unit as Web services.

12. Contemporary SOA supports a service-
oriented business modeling paradigm
Partitioning business logic into services that can then
be composed has significant implications as to how
business processes can be modeled (Figure).
Analysts can leverage these features by incorporating
an extent of service-orientation into business processes
for implementation through SOAs.

Figure :A collection (layer) of services encapsulating business process logic.

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Services can be designed to express business logic.
BPM models, entity models, and other forms of
business intelligence can be accurately represented
through the coordinated composition of business-
centric services.
13. Contemporary SOA implements layers of
abstraction
Typical SOAs can introduce layers of abstraction by
positioning services as the sole access points to a
variety of resources and processing logic.
When applied through proper design, abstraction can
be targeted at business and application logic.

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For example, by establishing a layer of endpoints that
represent entire solutions and technology platforms,
all of the proprietary details associated with these
environments disappear (Figure).
The only remaining concern is the functionality
offered via the service interfaces.

Figure :Application logic created with proprietary technology can be abstracted
through a dedicated service layer.

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It is the mutual abstraction of business and technology
that supports the service-oriented business modeling
paradigm we discussed and further establishes the
loosely coupled enterprise model explained in the
following section.
14. Contemporary SOA promotes loose coupling
throughout the enterprise
A core benefit to building a technical architecture with
loosely coupled services is the resulting independence
of service logic.
Services only require an awareness of each other,
allowing them to evolve independently.

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15. Contemporary SOA promotes organizational
agility
Change in an organization's business logic can impact
the application technology that automates it.
Change in an organization's application technology
infrastructure can impact the business logic automated
by this technology.
The more dependencies that exist between these two
parts of an enterprise, the greater the extent to which
change imposes disruption and expense.

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Figure :A loosely coupled relationship between business and application technology
allows each end to more efficiently respond to changes in the other.

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16. Contemporary SOA is a building block
A service-oriented application architecture will likely
be one of several within an organization committed to
SOA as the standard architectural platform.
Organizations standardizing on SOA work toward an
ideal known as the service-oriented enterprise (SOE),
where all business processes are composed of and exist
as services, both logically and physically.
When viewed in the context of SOE, the functional
boundary of an SOA represents a part of this future-
state environment, either as a standalone unit of
business automation or as a service encapsulating some
or all of the business automation logic.

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In responding to business model-level changes, SOAs
can be augmented to change the nature of their
automation, or they can be pulled into service-oriented
integration architectures that require the participation
of multiple applications.
17. Contemporary SOA is an evolution
SOA defines an architecture that is related to but still
distinct from its predecessors.
It differs from traditional client-server and distributed
environments in that it is heavily influenced by the
concepts and principles associated with service-
orientation and Web services.

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It is similar to previous platforms in that it preserves
the successful characteristics of its predecessors and
builds upon them with distinct design patterns and a
new technology set.
18. Contemporary SOA is still maturing
This point is obviously more of a subjective statement
of where SOA is at the moment.
Even though SOA is being positioned as the next
standard application computing platform, this
transition is not yet complete.

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19. Contemporary SOA is an achievable ideal
A standardized enterprise-wide adoption of SOA is a
state to which many organizations would like to fast-
forward.
The reality is that the process of transitioning to this
state demands an enormous amount of effort,
discipline, and, depending on the size of the
organization, a good amount of time.
Every technical environment will undergo changes
during such a migration, and various parts of SOA will
be phased in at different stages and to varying extents.
This will result in countless hybrid architectures,
consisting mostly of distributed environments that are
part legacy and part service-oriented.
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Defining SOA
 Now that we've finished covering characteristics, we
can finalize our formal definition.
Contemporary SOA represents an open, agile, extensible,
federated, composable architecture comprised of
autonomous, QoS-capable, vendor diverse, interoperable,
discoverable, and potentially reusable services,
implemented as Web services.
SOA can establish an abstraction of business logic and
technology that may introduce changes to business
process modeling and technical architecture, resulting in
a loose coupling between these models.

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SOA is an evolution of past platforms, preserving
successful characteristics of traditional architectures,
and bringing with it distinct principles that foster
service-orientation in support of a service-oriented
enterprise.
SOA is ideally standardized throughout an enterprise,
but achieving this state requires a planned transition and
the support of a still evolving technology set.
 Though accurate, this definition of contemporary SOA is quite
detailed. For practical purposes, let's provide a supplementary
definition that can be applied to both primitive and contemporary
SOA.

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SOA is a form of technology architecture that adheres to
the principles of service-orientation. When realized
through the Web services technology platform, SOA
establishes the potential to support and promote these
principles throughout the business process and
automation domains of an enterprise.

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Comparing SOA to client-server and
Distributed internet architectures

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Client Server Architecture
The original monolithic mainframe systems that
empowered organizations to get seriously
computerized often are considered the first inception
of client-server architecture.
These environments, in which bulky mainframe back-
ends served thin clients, are considered an
implementation of the single-tier client-server
architecture (Figure)

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Mainframe systems natively supported both synchronous
and asynchronous communication.
The latter approach was used primarily to allow the server
to continuously receive characters from the terminal in
response to individual key-strokes. Only upon certain
conditions would the server actually respond.
While its legacy still remains, the reign of the mainframe
as the foremost computing platform began to decline
when a two-tier variation of the client-server design
emerged in the late 80s.

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This new approach introduced the concept of delegating
logic and processing duties onto individual workstations,
resulting in the birth of the fat client.
The common configuration of this architecture consisted
of multiple fat clients, each with its own connection to a
database on a central server.
Client-side software performed the bulk of the processing,
including all presentation-related and most data access
logic (Figure).
One or more servers facilitated these clients by hosting
scalable RDBMSs.

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Figure: A typical two-tier client-server architecture.

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Primary characteristics of the two-tier client-server
architecture individually and compare them to the
corresponding parts of SOA.
Application Logic
 The Client Server architecture include fat client that does
bulk of processing and data-related logic and database server
lying on the server.
 In the case of SOA options exist regarding where the
application logic can reside and how it is distributed.

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Application Processing
The Client Server architecture follow 80/20 where bulk of
processing is done by the client and other database access
and connection pooling is done by the server .
In case of SOA, each service has a explicit functional
boundary and resource requirement.
Technology
Client Server Architecture make use of 4GL programming
languages and for performance reasons make use of 3GL
programming languages. They also use vendor based
RDBMS packages.
In case of SOA, XML data representation architecture along
with SOAP message framework. It makes use of
HTML,CSS,HTTP etc.
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Security
In case of the client server, the security is centralized
at the server side. But security can also be realized on
the client side.
SOA heavily depends on WS-security framework for
security.

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Administration
In client server architecture, the maintenance cost
are high and administration problems are also
involved.
SOA is also not that immune to client-side
maintenance challenges.

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SOA vs Traditional Distributed Internet Architecture
Distributed architecture consists of many
components but it reduces problem of centralization
on server.
It provides a dedicated servers which shares and
manages database connections.
Distributed architecture introduces a new physical
tier web server, which replaced HTTP by RPC
protocol to communicate between remote web and
application server

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Application Logic
SOA is similar to distributed architecture provider
logic lies in server side but difference lies in
principles.
Components are tight coupled and processing is
wasted to locate component at runtime whereas web
services are loosely coupled thus it introduces
opportunity for reuse and extensibility.

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Application Processing
Distributed architecture promotes proprietary
protocols like DCOM and CORBA for remote data
exchange.
It supports creation of stateful and stateless
components.
 SOA relies on message based communication, it
involves serialization and deserialization of SOAP
messages containing XML document payloads

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Technology
Distributed computing consists of components,
server side scripts and web technologies like HTML
and HTTP.
SOA consists of distributed objects using Xml and
web services.

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Security
Traditional security architectures includes
approaches like delegation and impersonation,
encryption to HTTP protocol.
SOA rely heavily extension and concepts provided by
WS-Security framework,
SOA emphasize on security logic.
SOAP messages provides header in security logic can
be stored.

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Administration
Distributed architecture introduces web server and
physical environment using HTTP.
SOA requires additional runtime administration.
Problems with messaging framework can go
undetected than with RPC based data exchange.

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Logic components of the Web services
framework
Web services contain
one or more operations.

Figure 8.4 as an
example

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framework
 Each operation governs
the process of a specific
function the web
service is capable of
performing.

 Figure 8.5 gives an
example of an
operation sending and
receiving SOAP
messages
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framework
Web services form an
activity though which
they can collectively
automate a task.

Figure 8.6 as an
example

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Logic components of automation
logic
Fundamental parts of Renamed terms
the framework
SOAP messages Messages
Web service operations Operations
Web services Services
Activities Processes

 Activity has been changed
because it uses a different context
when modeling service-oriented
business processes.

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logic
Messages = units of communication

Operations = units of work

Services = units of processing logic

Processes = units of automation logic

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logic
The purpose of these views
is to express the process,
services and operations.
Is also provides a flexible
means of partitioning and
modularizing the logic.
These are the most basic
concepts that underlies
service-orientation.

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Components of an SOA
Message
A message represents the data required to complete some
or all parts of a unit of work.

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Operation
An operation represents the logic required to process
messages in order to complete a unit of work.

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Service
A service represents a logically grouped set of operations
capable of performing related units of work.
Processes
A process contains the business rules that determine which
service operations are used to complete a unit of
automation.
A process represents a large piece of work that requires
the completion of smaller units of work.

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How components in an SOA inter-relate
An operation sends and receives messages to perform
work.

An operation is therefore mostly defined by the
message it processes.

A service groups is a collection of related operations.

A service is therefore mostly define by the operations
that comprise it.
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A process instance can compose service.

A process instance is not necessarily defined by its
service because it may only require a subset of the
functionality offered by the services.

A process instance invokes a unique series of
operations to complete its automation.

Every process instance is therefore partially defined
by the service operation it uses.
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Common principles of service-orientation
 Services are reusable

 Services share a formal contract

 Services are loosely coupled

 Services abstract underlying logic

 Services are composable

 Services are autonomous

 Services are stateless

 Services are discoverable
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Services are reusable
Regardless of whether immediate reuse opportunities
exist, services are designed to support potential reuse.
Service-oriented encourages reuse in all services.
By applying design standards that require reuse
accommodate future requirements with less
development effort.

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Services share a formal contract
For services to interact, they need not share anything but
formal contract that describe each service and define the
terms of information exchange.
Service contracts provide a formal definition of:
The service endpoint
Each service operation
Every input and output message supported by each
operation
Rules and characteristics of the service and its operations
Service contacts define almost all of the primary parts of
an SOA.
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Services are loosely coupled
Services must be designed to interact without the need
for tight, cross-service dependencies.

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Services abstract underlying logic
The only part of a service that is visible to the outside
world is what is exposed via the service contract.
Underlying logic, beyond what is expressed in the
descriptions that comprise the contract, is invisible and
irrelevant to service requestors.

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Services are composable
Services may be composing other services.
This allows logic to be represented at different levels of
granularity and promotes reusability and the creation
of abstraction layers.

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Services are autonomous
The services reside inside a well defined boundary
and for the successful execution of a service it does
not depend on other service for it to execute its
governance.

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Services are stateless
Service are not allowed to store the state information
as it will not allow the service to be loosely coupled.
Services should be designed to maximize
statelessness even if that means deferring state
management elsewhere.
Statelessness is a preferred condition for services and
one that promotes reusability and scalability.

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Services are discoverable
The service should allow their description to be
searched and understood by humans.

Figure :The UpdateEverything operation encapsulating a service composition.

01/20/13 Unit 1

SOA Unit I

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