J.A. Bakker and J.H. ter Bekke (Netherlands)
shortest path, recursive query, semantic model, transitiveclosure
This paper discusses how to extend the applicability of the recursive cascade update command of the Xplain query language. This command guarantees termination because cycle detection is included, which is in favor of end user computing. The execution of this command is based on graph reduction; therefore it can only be applied to acyclic graphs. Because flights constitute cycles between airports, it seemed impossible to specify a query language solution for shortest flight connections between two arbitrary airports. However, on a time scale cyclic connections between successive flights cannot exist at all. Therefore we designed an appropriate semantic data model for feasible connections between successive flights. Using this extended data model, the cascade command still enables end users to specify recursive queries for the fastest series of flights between any pair of airports.
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