Over the last two decades, information technology architectures and applications have increased in term of sizes and complexities. Nowadays, information systems are facing today stringent functional requirements such as flexibility, adaptability, maintainability, evolution. Driven by those constraints, the modern trend is to focus on standardized approach to integrate architectures of new applications with existing or legacy systems. This paper outlines the requirements and issues encountered while defining a Service Oriented Architecture based reference model, integrating two applications developed and used by the Norwegian statistic public agency.