442_MultiDimIndex

442_MultiDimIndex - MultidimensionalIndexes...

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Multi-dimensional Indexes
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Types of Spatial Data Point Data Points in a multidimensional space E.g.,  Raster data  such as satellite imagery, where each  pixel stores a measured value E.g., Feature vectors extracted from text Region Data Objects have spatial extent with location and boundary DB typically uses geometric approximations constructed  using line segments, polygons, etc., called  vector data .
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Types of Spatial Queries Spatial Range Queries Find all cities within 50 miles of Madison Query has associated region (location, boundary) Answer includes ovelapping or contained data regions Nearest-Neighbor Queries Find the 10 cities nearest to Madison Results must be ordered by proximity Spatial Join Queries Find all cities near a lake Expensive, join condition involves regions and proximity
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Applications of Spatial Data Geographic Information Systems (GIS) E.g., ESRI’s ArcInfo; OpenGIS Consortium Geospatial information All classes of spatial queries and data are common Computer-Aided Design/Manufacturing Store spatial objects such as surface of airplane fuselage Range queries and spatial join queries are common Multimedia Databases Images, video, text, etc. stored and retrieved by content First converted to  feature vector  form; high dimensionality Nearest-neighbor queries are the most common
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Single-Dimensional Indexes B+ trees are fundamentally  single-dimensional  indexes. When we create a composite search key B+ tree, e.g., an index on  <age, sal> , we effectively linearize the 2-dimensional space since  we sort entries first by  age  and then by  sal. Consider entries: <11, 80>, <12, 10> <12, 20>, <13, 75> 11      12      13 70 60 50 40 30 20 10 80 B+ tree order
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Using B+-tree to index multi- dimensional data Use of space-filling curves to organize points.  Assume attribute values can be represented with  fixed number of bits (discrete attribute values) Visit all points in space
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Space-filling curve: Z-ordering Interleaves x-axis bits and  y axis bits: X=00, Y=10, Z=0100  (4) X=10, Y=11, Z=1101  (13) Long diagonal jumps 00 10 01 11 00 01 10 11
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Fractal recursive curve. Tends to be better than Z-
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This note was uploaded on 02/24/2011 for the course CS 442 taught by Professor Mlittman during the Fall '08 term at Rutgers.

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442_MultiDimIndex - MultidimensionalIndexes...

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