The appearance of web affected the ways that people interchange the information and use it. In order to explore through infinite documents in the web, an evolution is required. This evolution is nothing but the semantic web, which is processing of semantics and meanings by computer. The backbone of semantic web is consisted of ontology, which is a taxonomy or dictionary of concepts and meanings that can be processed by computer. Ontology changes and improvements are inevitable. These changes can be considered as changes in graphs and trees. While currently most ontology graphs are distributed over the web, change management of these graphs turns to a vital concern.