This paper summarizes our ongoing effort to understand and characterize the uses of multiple perspectives in space science. We have attempted to bring together a variety of theories and research areas practiced by a variety of communities with apparently very limited cross-fertilization to date. For example, the combination of different levels of reasoning is widely recognized as being desirable in sensor data fusion applications. However, we have not found a unifying account of the variety of possible approaches. In this effort, we try to perform such an accounting using the notion of ontology. Ontologies serve as a unifying device in a study of perspectives because they help to formalize the notion of an interpretation. There have been previous formalizations of the notions of observation and interpretation, such as Bennett et al (1989), but these have focused mostly on the quantitative treatment of uncertainty, rather than on the logical structure of an interpretation. Ontologies help in providing a logical treatment. By doing so, they provide a framework for integrating higher-level reasoning approaches.