Service Oriented Architecture (SOA) can be described as an architectural style or strategy of “building loosely coupled distributed systems that deliver application functionality in the form of services for end-user applications” (Ho, 2003). Ho (2003) proclaims that a service can be envisioned as a simple unit of work as offered by a service provider. The service produces a desired end result for the service consumer. Another way to envision the concept of a service is to imagine a “reusable chunk of a business process that can be mixed and matched with other services” (Allen, 2006). The services either communicate with each other (i.e. pass data back and forth) or work in unison to enable or coordinate an activity.
When SOA is employed for designing applications and/or IT systems, the component services can be reused across the enterprise, which helps to lower overall development costs amongst other benefits. Reuse fosters consistency across the enterprise. For example, SOA enables banks to meet the needs of small, but profitable market segments without the need to redevelop new intelligence for a broad set of applications (Earley, Free & Kun, 2005). Furthermore, any number of services can be combined together to mimic a business processes.
“One of the most important advantages of a SOA is the ability to get away from an isolationist practice in software development, where each department builds its own system without any knowledge of what has already been done by others in the organization. This ‘silo’ approach leads to inefficient and costly situations where the same functionality is developed, deployed and maintained multiple times” (Maréchaux, 2006).
Services are only accessed through a published application-programming interface, better known as the API. The API, which acts as the representative of the service to other applications, services or objects is “loosely coupled” with its underlying development and execution code. Any outside client invoking the service is not concerned with the service’s development code and is hidden from the outside client. “This abstraction of service implementation details through interfaces insulates clients from having to change their own code whenever any changes occur in the service implementation” (Khanna, 2008). In this manner, the service acts as a “black box” where the inner workings and designs of the service are completely independent from requestors. If the underlying code of the service were switched from java to C++, this change would be completely oblivious to would-be requestors of the service.
Allen, (2006) describes the concept of loose coupling as, “a feature of software systems that allows those systems to be linked without having knowledge of the technologies used by one another.” Loosely coupled software can be configured and combined together with other software at runtime. Tightly coupled software does not offer the same integration flexibility with other software, as its configuration is determined at design-time. This design-time configuration significantly hinders reusability options. In addition, loosely coupled applications are much more adaptable to unforeseen changes that may occur in business environments.
In the early 1990’s some financial firms adopted an objected oriented approach to their banking architecture. This approach is only superficially similar to a service oriented architecture approach. In an object oriented (OO) approach, the emphasis is on the ability to reuse objects within the source code. SOA emphasizes a “runtime reuse” philosophy in which the service itself is discoverable and reused across a network (Earley, Free & Kun, 2005). SOA also provides a solution to the lack of interoperability between legacy systems.
Allen, P. (2006). Service orientation: winning strategies and best practices.
Early, A., & Free, D., & Kun, M. (2005, July 1). An SOA Approach Will Boost a Bank’s Competitiveness (ID: G00126447). Retrieved from Gartner database.
Ho, H. (2003). What is Service-Oriented Architecture? O’Reilly XML.com.
Khanna, Ayesha. (2008). Straight through processing for financial services: the complete guide.
Maréchaux, J., (2006, March 28). Combining Service-Oriented Architecture and Event-Driven Architecture using an Enterprise Service Bus. IBM developerWorks. Retrieved from http://www.ibm.com/developerworks/library/ws-soa-eda-esb/