Abstract

syntax level. At this level, we apply source-to-source transformations to reduce the number of edges that must be traversed in the input graph. We do this by finding common prefixes in multiple regular path expressions. For example, consider: where Root(p); p ("A":"B"):"A" q; p "A":"C":"D" r We can rewrite the first regular expression into an equivalent expression: where Root(p); p "A":("B":"A") q; p "A":"C":"D" r Next, we introduce two node variables, x and y: where Root(p); p "A" x; x ("B":"A") q; p "A" y; y "C":"D" r Finally, if q and r are "independent", meaning that none of the clauses in link creates and edge between them, then we can collapse the x and y node variables into a single variable z, and get: where Root(p); p "A" z; z ("B":"A") q; z "C":"D" r The resulting query is equivalent to the original, but it traverses each edge "A" accessible from the root once. Automaton level. At this level, each regular expression is translated into a generalized NDFA. There is one ...

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