An emerging trend in Web computing aims at collecting and integrating distributed data. For instance, community driven efforts recently have build ontological repositories made of large volumes of structured and interlinked data from various Web sources. Those repositories are extreme in the sense that they are extraordinary in size and dominated by assertional data incorporating only a small and typically lightweight schema. So far, users can find tools for building and browsing through large schemas but there is virtually no support in navigating, visualizing or even analyzing the data part of such a structured repository appropriately. This paper describes how to combine techniques from visual analytics and logical reasoning for interactive exploration of large volumes of interrelated data. Our approach utilizes bstraction techniques, semantical filters, as well as various level of detail information. The underlying visualization rationale is driven by the principle of providing de...