Good Decision Support Systems require three main features: (i) a good handling of the domain data and information; (ii) an efficient user interface; and (iii) a good knowledge of past decisions. Usually such features are handled by different specialized systems difficult to integrate. In this research we keep specialized systems independent, focusing on interoperability. We propose a system of systems architecture (SoS) integrating a domain system in which users interact, a multi-agent system implementing an efficient user interface and taking into account results from the domain system, and a platform to capitalize and manage knowledge. Our approach extracts indicators from the interaction or behavior of users within the domain system, and provides them analyses, statistics and recommendations to help them reach good decisions. We built a prototype and applied it to two different domains: collaborative software development and healthcare. In this paper, we will focus on the multi-agent system which is a key component of the SoS architecture.