Gaining an overview of the concepts represented in large programs is very demanding as multiple dimensions of knowledge appear at different abstraction levels throughout the source code. To reduce the overall comprehension effort it is therefore desirable to make the knowledge once gained explicit and shareable. We tackle this problem by establishing a mapping between source code and conceptualizations shared as ontologies. To achieve this we regard programs themselves as knowledge bases built on the programs? identifiers and their relations implied by the programming language. Making these mappings explicit allows sharing knowledge about the concepts represented in programs. We exemplify our approach on Java programming language and the WordNet ontology and we report on our experience with analyzing an open source system.