As I
mentioned in the earlier post, following are the questions that I frequently encounter and was trying to find common sense answers for

• I have heard about it so much,
  but what exactly is SOA?
• What is a Service?
• What exactly do you mean when
  you say Service Oriented?
• What do you mean by Composite
  Services?
• What do you mean by Service
  Orchestration?
• What is different about
  Service Oriented approach for Enterprise Integration?
• How is one company's SOA
  different than the other?

So as I
thought while posting my first blog entry I did take a step back and revisited
the concepts from a common sense perspective to share my understanding. Here it is my experiment and thoughts shared...

Service
Oriented Architecture: The Beginning

What is a Service?

Service
means the performance of any duties or work for another. Service is provided by
a service provider and consumed by the service consumer. Simple!

Think
about it. We all use and provide services almost everyday in our day today
life.  Following are some examples of well-known services:

Service Provider: Government
Services Provided: Education Services,
Infrastructure Services, Police and Fire Services, Postal Services, and other
regulatory services

Service Provider: Financial Companies
Services Provided: Accounting Services,
Banking Services, Tax Services, and auditing services

Service Provider: Utility Companies
Services Provided: Electricity Services, Gas
Services, Communication Services, Water Services, and Waste Management services


Service Provider: Individuals
Services Provided: Employee Services (various
roles), Medical Services, Law and Attorney Services

One of
the formal definition of services in a business sense is �Service is any act
or performance that one party can offer to another that is essentially in
tangible and does not result in the ownership of anything.�

What is service oriented?

Any
approach simple or composite based on services and/or service-mix is service
oriented. So is it anything new? No, Actually we already live in a service
oriented world and Service oriented approach is so very common in our
surroundings. It exists universally and is the most fundamental functional
aspect of human life in our society. Service providers and consumers range from
an individual person to giant multinational corporations. Most companies
provide services that are outcome of services provided to them by individual
employees and may be other companies. Service oriented societies and cultures
demonstrate some common characteristics such as standard currencies,
governance, service composition, and service orchestration.

Before
we talk about Service Oriented approach for software architecture, let�s see
how some of the principles apply in real life example. Let�s go through my
example:

My Example of Service: Flight
Service

I
live in Denver and fly for work to customer locations frequently, the obvious
real life example I was able to think of was of an airline and the service
(flight) it provides. Let�s take an example of a service I have used often,
flight between Denver and San Francisco.

Thinking
from service perspective, the airline I use is the Service Provider of the
flight between Denver and San Francisco. Since I choose to pay for the flight
and use the service, which makes me the service consumer.

In
this example some of the things to note as they relate to SOA are the
following:

Service Abstraction

The
airline uses multiple services, goods, and equipments to provide this service
to the customers. The service in itself is very complex technically and is
composed of several other services. But from my perspective there is a well defined
but simple interface to consume this service. All I need to care about is
making the payment for ticket and be on time at the correct Airport and gate :)

I
don�t have to worry about paying the Airport for the services such as security,
gate fees, air traffic control, and the airline in-flight services. I also
don�t worry about how the airline manages their employees, equipment, goods,
and other services that they consume to provide me with this service.

This
demonstrates the concept of abstraction. Services abstract the logic and
implementation.

Service Loose Coupling

Abstraction
promotes loose coupling of services. As services are modular, logic contained
in them is independent of each other. Awareness of the service is enough for
the services to interact and thus they are loosely coupled. They can change
within their own boundaries without causing any change required to the
consumer.

In
my example, most of the individual services are loosely coupled and communicate
using standard interfaces. The airline relies on the services provided by
Airport for security and ATC, it does not actually know or have to interact
with specific persons providing these services. Airport can very well replace
the security and ATC personals and still provide the same service without any
awareness required on the service consumers side. Loose coupling is one of the
most important concepts of SOA.

Service Contract

Service
should be defined and be agreed upon by the provider and consumer. My airline
in this example agrees to provide me a seat in economy class, provide me with
the standard in-flight service, and fly me from Denver airport�s particular
gate to the SFO airport. I agree to this service by buying the ticket using
standard currency (USD in this case). I also agree to be physically present at
the airport at the defined time, look up for the gate information, go through
the security and walk to the defined gate. Besides the basic known things,
there is a formal contract between me and airline (service provider and the
consumer). Some of the standards components of service definition in our
example are Airports, Flight Numbers, Currency, and Security.

Service Discovery

The
airline that provide me this service is listed on my corporate travel web site
as well as other standard and known interfaces and thus can be discovered by me
or any other customer. The service should be discoverable.

Service Composition

The
airline service is composed of several other services internally. To provide
the service (flying between Denver and San Francisco) to me and other
customers, the airline uses various services from multiple service providers.
Following are the main category of services that are used by our airline to
provide the flying service

• Airport Services
• Employee Services
• Food Catering Services
• Entertainment Services
  

Following diagram represents the Service that is composed of several other
services. Thus the end service that I use is a composite service.

Like the diagram depicts, one service can be composed of multiple service components internally. There is a layer of abstraction and thus the consumer of the service does not need to know the details. SOA is based on the principle of Service Composition.

Service Orchestration

In a music world, the person orchestrating a music orchestra symphony decides what music
instrument is to be played and when it plays what is the note that it should
play. In our example, the flight service has to be perfectly orchestrated to
provide the desired level of customer satisfaction. Our
airline has to use internal and external services in an ordered and defined way
as a process flow. Every service component like drinks, video, audio, announcements are well planned and orchestrated. The airline decides the process flow, execution, and timing of
services that we noticed in the diagram above for service composition. Every
process in the service has to be executed in a perfect order and style.

This is Service Orchestration and is a very important component of SOA.

Important Characteristics of
Service Orientation

Based on my understanding I came up with the following main characteristics or Service Orientation

• Service
  Discoverability
• Service
  Interactions and Amalgamation supported by Open Standards
• Service
  Composition
• Service
  Abstraction
  
• Service
  Loose Coupling
• And
  also importantly Service Real World Effects

What is Service Oriented
Architecture?

If
we are already living in a world that works based on service oriented approach,
what is so different about applying it to software architecture? What is the
entire buzz about?

SOA
is a simple and common sense approach adopted from the way things work in our
surroundings to the more complex, tightly coupled, and rigid world of software.

SOA
as it relates to software paradigm is an agile architecture approach that is
based on service-oriented principles of composition, abstraction, loose
coupling, discoverability, and amalgamation. SOA inherently empowers
scalability, evolution of services, interoperability, reusability, and
modularity.

Why is SOA Needed?

Simplicity
is desired for the traditional and complex IT world. Better and common sense
approaches should be enabled. SOA is needed for the following main reasons:

• To provide seamless agility to business
  
• To improve business process visibility
  
• To simplify the current rigid and complex state of IT
• To enhance efficiency and provide cost-effectiveness
• To enable reusability factor
• To provide better quality of service

How is one company's SOA
different than the other?

SOA as such is not a product that
can be bought, rather is an approach towards building modular software using
service-oriented principles. There are tools that can be used to realize the
service-oriented approach efficiently. Many companies provide tools for
assisting enterprise software implementation based on services and
service-oriented architecture approach. In case of Oracle, the components for SOA are bundled as SOA Suite which is a complete set of service infrastructure components for building, deploying, and managing SOAs.

Find more about Oracle SOA Suite