Querying graph structured data is a fundamental operation that enables important applications including knowledge graph search, social network analysis, and cyber-network security. However, the growing size of real-world data graphs poses severe challenges for graph databases to meet the response-time requirements of the applications. Planning the computational steps of query processing - Query Planning - is central to address these challenges. In this paper, we study the problem of learning to speedup query planning in graph databases towards the goal of improving the computational-efficiency of query processing via training queries.We present a Learning to Plan (L2P) framework that is applicable to a large class of query reasoners that follow the Threshold Algorithm (TA) approach. First, we define a generic search space over candidate query plans, and identify target search trajectories (query plans) corresponding to the training queries by performing an expensive search. Subsequently, we learn greedy search control knowledge to imitate the search behavior of the target query plans. We provide a concrete instantiation of our L2P framework for STAR, a state-of-the-art graph query reasoner. Our experiments on benchmark knowledge graphs including DBpedia, YAGO, and Freebase show that using the query plans generated by the learned search control knowledge, we can significantly improve the speed of STAR with negligible loss in accuracy.
A safety locking cover assembly for the dome of a tank truck of the type adapted to carry inflammable liquids. A cover is hinged upon a base attachable to the tank dome, and is moved between opened and closed positions by upward pivotal movement of a semicircular handle. The opposite ends of the handle pivot upon a locking bar extending beneath the cover top. The ends of the bar project from opposite sides of the cover and extend into recesses in catches mounted to the base, thereby normally preventing upward movement of the cover relative to the catches. However, the catches are spring biased against the base and are upwardly movable against the spring bias by high internal tank pressures. This provides a relatively large vent opening to vent the tank despite the fact that the handle may be closed. The cover can be manually opened by pivoting the handle through a 180 DEG arc. This moves the locking bar downwardly relative to the catches on the base. This allows limited upward vertical movement of the locking bar and cover relative to the catches and any slight buildup of internal tank pressure is relieved before the cover is hinged upwardly to its open position. Movement of the pivoted handle circumferentially in the plane of the cover positions the locking bar out of alignment with the restraining catches and the cover can be hingedly moved to an open position. Alternative rapid mounting and demounting means for the tank dome are also disclosed.