...4] summarizes the paths of OEM. Graphs are considered as NFA and their DATAGUIDEs are DFA of the graphs. DATAGUIDE is extended to support approximate query processing [8]. Straight-Line Grammar (STL) =-=[6]-=- is a special form of context-free grammar, for summarizing a data graph. To reduce the grammar size, [6] proposes to use a wildcard to simplify some non-terminals in a production. Another graph-based...