OntospyWeb is a tool made for navigating ontologies ('vocabularies') encoded using the RDF family of languages. It is based on the Ontospy Python library, which in turns wraps RDFLib.
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P. Martin. Conceptual Structures: Standards and Practice: 7th International Conference on Conceptual Graphs, 1867, page 41-54. Springer Verlag, (2000)Detailed description of the notational conventions used for knowledge engineering in WebKB-2.