QC-Tree is one of the most storage-efficient structures for data cubes in an MOLAP system. Although QC- Tree can achieve a high compression ratio, it is still a fully materialized data cube. In this paper, an improved...QC-Tree is one of the most storage-efficient structures for data cubes in an MOLAP system. Although QC- Tree can achieve a high compression ratio, it is still a fully materialized data cube. In this paper, an improved structure PMC is presented allowing us to materialize only a part of the cells in a QC-Tree to save more storage space. There is a notable difference between our partially materialization algorithm and traditional materialized views selection algorithms. In a traditional algorithm, when a view is selected, all the cells in this view are to be materialized. Otherwise, if a view is not selected, all the cells in this view will not be materialized. This strategy results in the unstable query performance. The presented algorithm, however, selects and materializes data in cell level, and, along with further reduced space and update cost, it can ensure a stable query performance. A series of experiments are conducted on both synthetic and real data sets. The results show that PMC can further reduce storage space occupied by the data cube, and can shorten the time to update the cube.展开更多
Some physicists depicted the molecular structure SnCl_2 · 2（H_2O） by a piece of an Archimedean tiling（4.8.8） that is a partial cube. Inspired by this fact, we determine Archimedean tilings whose connected sub...Some physicists depicted the molecular structure SnCl_2 · 2（H_2O） by a piece of an Archimedean tiling（4.8.8） that is a partial cube. Inspired by this fact, we determine Archimedean tilings whose connected subgraphs are all partial cubes. Actually there are only four Archimedean tilings,（4.4.4.4）,（6.6.6）,（4.8.8） and（4.6.12）, which have this property. Furthermore, we obtain analytical expressions for Wiener numbers of some connected subgraphs of（4.8.8） and（4.6.12） tilings. In addition, we also discuss their asymptotic behaviors.展开更多
基金Supported by the National Key Scientific and Technological Project： Research on the Management of the Railroad Fundamental Information （Grant No.2002BA407B01-2） and the Science Foundation of Beijing Jiaotong University （Grant No.2003SZ003）.
文摘QC-Tree is one of the most storage-efficient structures for data cubes in an MOLAP system. Although QC- Tree can achieve a high compression ratio, it is still a fully materialized data cube. In this paper, an improved structure PMC is presented allowing us to materialize only a part of the cells in a QC-Tree to save more storage space. There is a notable difference between our partially materialization algorithm and traditional materialized views selection algorithms. In a traditional algorithm, when a view is selected, all the cells in this view are to be materialized. Otherwise, if a view is not selected, all the cells in this view will not be materialized. This strategy results in the unstable query performance. The presented algorithm, however, selects and materializes data in cell level, and, along with further reduced space and update cost, it can ensure a stable query performance. A series of experiments are conducted on both synthetic and real data sets. The results show that PMC can further reduce storage space occupied by the data cube, and can shorten the time to update the cube.
基金Supported by the National Natural Science Foundation of China under Grant No.11471273 and No.11271307Youth Research Fund Project of Chengyi College of Jimei University under Grant No.CK17007
文摘Some physicists depicted the molecular structure SnCl_2 · 2（H_2O） by a piece of an Archimedean tiling（4.8.8） that is a partial cube. Inspired by this fact, we determine Archimedean tilings whose connected subgraphs are all partial cubes. Actually there are only four Archimedean tilings,（4.4.4.4）,（6.6.6）,（4.8.8） and（4.6.12）, which have this property. Furthermore, we obtain analytical expressions for Wiener numbers of some connected subgraphs of（4.8.8） and（4.6.12） tilings. In addition, we also discuss their asymptotic behaviors.
