It’s not unusual to find confusion between Service Oriented Architecture, SOA, and IT Services. SOA is a methodology used to take advantage of re-use and ease of maintenance. IT Services on the other hand is a broad term used to describe a deliverable (e.g. database, a website) from an IT Functional Area.
SOA is a design protocol that makes a frequently used business function available to many disparate systems. SOA functions are ‘made available’ through protocols or APIs and implement a self-contained set of business functionality. SOA modules don’t call other programs but rather work on the data it gets and provides a result. It’s an efficient way to design and build an application. A set of loosely coupled functions can be cobbled together to build an application.
Re-use and ease of maintenance are achieved when the same function (i.e. program code) is used to build multiple applications. Managing changes to functions implemented using SOA is easier because when you change the function in one place (i.e. program code), all consumers of that function are the updated. Data is typically moved between services via well defined APIs.
SOA is a development and design methodology for designing solutions. This is the level of programming that implements business rules and requirements. IT Services on the other hand, provide the environment used by the solutions built with SOA. An IT Service is a tangible deliverable from IT. SOA provides the components necessary for building and delivering Business Solutions.