1. A system including instructions recorded on a non-transitory computer-readable medium, and executable by at least one processor, the system comprising: a query collector configured to cause the at least one processor to receive a plurality of queries applied by a search engine to obtain corresponding search results; a graph manager configured to cause the at least one processor to generate, based on the plurality of queries, a directed graph of nodes, each node corresponding to at least one query and connected to another node, and further configured to cause the at least one processor to merge at least two of the nodes based on a similarity of corresponding queries thereof, to obtain a merged node, and generate at least one representative query representing the merged node; and a suggestion generator configured to cause the at least one processor to match a current query with a matching node of the nodes, determine that the merged node is a successor node of the matching node within the directed graph, and provide the at least one representative query as a suggested query for a future search to be conducted by the search engine.