Digital Ecosystem (DE) is a concept emerged from the natural existence of business ecosystem, which in turn is taken from the concept of biological ecological systems. On the other hand, System of Information Systems (SoIS) are special type of System of Systems (SoS) that deals with several Information Systems producing overwhelming amount of information. In this paper we aim to define the concepts of DE, SoS, and SoIS. Then, provide the guidance for moving from Digital Ecosystem to System of Information Systems. Thus, we aim to draw the link between the model of DE presented in literature and the concept of SoS and SoIS. Then, we propose an architectural model of System of Information Systems (SoIS) and investigate the knowledge base role in such complex system operating in the environment of a Digital Ecosystem. These complex Digital Ecosystems pose a significant technical improvement in terms of information interoperability that overcomes conceptual and technical barriers. In this paper we are moving from Digital Ecosystem to System of Information Systems by defining the similarities between the two concepts, then proposing an architectural model of SoIS in correspondence to DE model.