Some document says OrientDB is document-database, some others talks it's graph-database. What's right?
According to a conversation with Luca Garulli, OrientDB creator, it is both a document and graph database. The complete discussion is available here providing more details on how OrientDB operates internally: http://nosql.mypopescu.com/post/1254869909/correction-orientdb-is-a-document-and-graph-store
Orient DB is Document-Graph (and/or) DBMS. According to the comparison with MongoDB, OrientDB can store data as JSON type documents but with one (out of many) added benefit of keeping track of relationships as links, to form a graph.