Ontology summarization is very important to quick understanding and selection of ontologies. In this paper, we study extractive summarization of ontology. We propose a notion of RDF sentence as the basic unit of summarization. An RDF Sentence Graph is proposed to characterize the links between RDF sentences derived from a given ontology. The salience of each RDF sentence is assessed in terms of its "centrality" in the graph. We propose to summarize an ontology by extracting a set of salient RDF sentences according to a re-ranking strategy. We compare several measurements in assessing the salience of RDF sentences and give an overall evaluation of experiment results, which shows that our approach to ontology summarization is feasible. Categories and Subject Descriptors I.7.m [Computing Methodologies]: Document and Text Processing--Miscellaneous; I.2.4 [Artificial Intelligence]: Knowledge Representation Formalisms and Methods--Representation languages General Terms Algorithms,...