Web Services and Service-oriented architecture are emerging distributed computing paradigms to publish and access software components as services. Various enterprises now publish their business as web services. Business processes of these enterprises involved in B2B and B2C transactions require composition of distributed heterogeneous services to accomplish a task. Business processes are complex, dynamic and event-driven. Dynamic composition and automation of complex business processes are becoming active areas of research in this field. Interoperable integration, immaturity, lack of semantic support amongst standards, scalability and middleware support are the challenges involved when business processes are evaluated at national scale. In this paper we propose semantic and rule based event-driven service-oriented architecture for automation of business processes. Semantic provides knowledge and vocabulary of domain and ECA rules are designed to generate the composition schema automatically and dynamically according to the events. We have taken real-life example of agricultural business for demonstration of our architecture.