Coordination and operational bodies involved in maritime surveillance need a common integrated maritime picture for performing their duties in an effective and cost-efficient way. Emerging trends for building an integrated maritime picture are focused on the adoption of a network-centric approach by leveraging on Service Oriented Architecture models and technological standards. This work presents results in the design and development of a message- and service-oriented middleware (named SAI - Service Application Integration - system), endowed with scalability, security and dependability capabilities. A demonstrator has been built in order to assess the SAI system capabilities for enabling information search and integration in the maritime surveillance scenario.