The objective of software systems (or simply Information Technology (IT) systems) in an enterprise is to support the enterprise' business. We have seen their architectures evolving from single-tier monolithic to multi-tier ones and with increasing abstractions. Still, as far as the flexibility of the system is concerned, they are found wanting. The demands on the flexibility of the systems have only been growing with the increasing pace in the changes in the business processes. Same holds for the gap between the system and the business it is intended to support. This needs a better suited architecture approach when we architect IT systems. We want the system to be very amenable to change, whenever there is a change in the business process. We need the system to be easier to support - we should be able to make the changes quickly. We expect the system to faithfully reflect the business process that it is intended to support.

Is there an architecture style that enables us to architect systems this way? Yes, Process-Centric Architecture (PCA).

PCA is an architectural style for software systems. It puts the business process at the center of the architecture of the system and lets it drive the system behavior at run-time. In PCA, the process logic of the application or the IT system is abstracted out into a separate component, thus providing  better flexibility and making the IT system reflect the business process directly as defined by the business - the system remains faithful to the business process. It makes the business process the core component of the system. Unlike the conventional architectural approaches where it was implicit and hardwired in the code, the process logic thus becomes explicit in PCA, separate from rules logic, business logic, user interaction logic, and database logic. It advocates an architectural design approach where the architectural design always starts with the business process at the top and proceeds top-down to other components.

The book Process-Centric Architecture for Enterprise Software Systems explains this architectural style in good detail. It is available here: http://www.amazon.com/Process-Centric-Architecture-Enterprise-Software-S....

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