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
used to 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
Discover-ability
·
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, discover-ability, 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.
