Patterns: Implementing Self-Service in an SOA Environment

24 Patterns: Implementing Self-Service in an SOA Environment

3.1 Overview of SOA

SOA defines integration architectures based on the concept of a service.

Applications collaborate by invoking each others services, and services are

composed into larger sequences to implement business processes.

The drive for SOA

The main driver for SOA is to define an architectural approach that assists in the

flexible integration of IT systems. Organizations spend a considerable amount of

time and money trying to achieve rapid, flexible integration of IT systems across

all elements of the business cycle. The drivers behind this objective include:

򐂰 Increasing the speed at which businesses can implement new products and

processes, can change existing ones, or can recombine them in new ways

򐂰 Reducing implementation and ownership costs of IT systems and the

integration between them

򐂰 Enabling flexible pricing models by outsourcing more fine-grained elements of

the business than were previously possible or by moving from fixed to

variable pricing, based on transaction volumes

򐂰 Simplifying the integration work that is required by mergers and acquisitions

򐂰 Achieving better IT use and return on investment

򐂰 Achieving implementation of business processes at a level that is

independent from the applications and platforms that are used to support the

processes

SOA prescribes a set of design principles and an architectural approach to

achieve this rapid, flexible integration.

Definition of SOA

SOA is an integration architecture approach that is based on the concept of a

service. The business and infrastructure functions that are required to build

distributed systems are provided as services that collectively, or individually,

deliver application functionality to either user applications or other services.

SOA specifies that within any given architecture, there should be a consistent

mechanism by which services communicate. That mechanism should be loosely

coupled and should support the use of explicit interfaces.

SOA brings the benefits of loose coupling and encapsulation to integration at an

enterprise level. It applies successful concepts that are proven by

Object-Oriented development, Component-Based Design, and Enterprise

Chapter 3. SOA and the Enterprise Service Bus 25

Application Integration technology to an architectural approach for IT system

integration.

Services are the building blocks to SOA. They provide the function out of which

you can build distributed systems. Services can be invoked independently by

either external or internal service consumers to process simple functions or can

be chained together to form more complex functionality and to quickly devise

new functionality.

By adopting an SOA approach and implementing it using supporting

technologies, you can build flexible systems that implement changing business

processes quickly and make extensive use of reusable components.

Figure 3-1 illustrates a company that wants to implement a new business

process to support customers who place orders from a Web site.

Figure 3-1 A service-oriented approach to building systems

The company already has existing retail, warehouse, and billing systems. It

would like to build the new process by reusing the functionality that is provided by

those systems, rather than having to write new applications or new interfaces to

the existing systems.

If the company has already adopted an SOA approach, it will have defined the

interfaces to its existing systems in terms of the functions or services that they

can offer to support the building of business processes. The defined interfaces

makes building the new Web front end to the system very simple. All the

company needs to do is to develop an application that makes calls to the

services to complete the new business process.

Business

Process

Bill

Customer

Defined

Services

Receive

Order

Service

Customer

Billing

Service

Fulfill

Order

Service

Restock

Service

IT

Systems

Web

Application

Retail

System

CRM

Warehouse

System

Receive

Order

Fulfill

Order

Restock