The difference between these development methodologies is basically one of scale. Procedural programming works just fine on very small projects. However, as the complexity of the project grows, the procedural paradigm begins to break down.
This is where object-oriented programming steps up to the plate. Using OOP, the developer is able to successfully manage more complex applications. However, as the complexity continues to grow, then OOP begins to suffer as well. This is easily seen when the inheritance hierarchy begins to be quite deep.
Component-oriented design focuses on delivering an application that is composed of components. These components interact via events. Component-oriented design builds on top of object-oriented design principles in that the components themselves are built using OOP.
Service-oriented programming takes this one step further. Using a service-oriented architecture allows the application developer to focus on what an application does (a service) versus what an application is or has (components and objects). Again, in SOA, you use the principles learned in OOP and COP to build your application, but the focus becomes on delivering a service. Services themselves are all about solving a business domain problem. Using an SOA approach, very complex, dynamic applications can be successfully developed, deployed, and maintained.
This was first published in February 2003