  A temporal graph is a graph in which connections between vertices are active
at specific times, and such temporal information leads to completely new
patterns and knowledge that are not present in a non-temporal graph. In this
paper, we study traversal problems in a temporal graph. Graph traversals, such
as DFS and BFS, are basic operations for processing and studying a graph. While
both DFS and BFS are well-known simple concepts, it is non-trivial to adopt the
same notions from a non-temporal graph to a temporal graph. We analyze the
difficulties of defining temporal graph traversals and propose new definitions
of DFS and BFS for a temporal graph. We investigate the properties of temporal
DFS and BFS, and propose efficient algorithms with optimal complexity. In
particular, we also study important applications of temporal DFS and BFS. We
verify the efficiency and importance of our graph traversal algorithms in real
world temporal graphs.
