Slideshow:
What is a Grid Index file
Structure of a Grid Index file
Grid lines and
grid buckets
Grid line = point interpretation
Grid line = interval endpoint interpretation
Grid Index file - Example
Grid Index file - Example
Grid Index file - Example
Grid Index file - Example
Comment on the representation used by the text book...
Grid file for higher dimensions
A 3-dimensional ("cube") Grid Index file:
- Grid Index file:
- Grid index file =
an index that is
organized into a
2-dimensional structure:
Notice that:
- Geographically "related" data (i.e.: points that are close to each other) are stored in the same data block !!!
- Grid index file =
an index that is
organized into a
2-dimensional structure:
- Storage structure of
a grid index file:
- A grid index file first stores
the size parameters m and n
of the grid
- Then the index file stores the
buckets
of the grid:
- v1, v2, ... vm
- x1, x2, ... xn
- Finally, the index file contains
m × n
block pointers
- Graphically:
- A grid index file first stores
the size parameters m and n
of the grid
- Grid lines and
buckets:
- 2 interpretations the
grid lines
- You can interpret the
values:
- x1, x2, ... xn
- v1, v2, ... vm
in 2 ways:
- As individual points
- As intervals
- You can interpret the
values:
- Point interpretation:
- The bucket pointer in
bucket (v, x)
points to
data blocks that
store
search key values:
key1 = v key2 = xExample:
The grid lines represents discrete values
(With n grid lines you will have n index points)
- The bucket pointer in
bucket (v, x)
points to
data blocks that
store
search key values:
- Interval interpretation:
- The bucket pointer in
bucket (vi, xj)
points to
data blocks that
store
search key values:
vi-1 ≤ key1 < vi xj-1 ≤ key2 < xj(With additional edge buckets that covers the entire range of values)
- Example:
The grid lines represents end points of intervals
(With n grid lines you will have n+1 intervals)
- The bucket pointer in
bucket (vi, xj)
points to
data blocks that
store
search key values:
- Data on people
who buy jewelry:
(age, salary (in $1,000)) A(25,60) D(45,60) G(50,75) J(50,100) B(50,120) E(70,110) H(85,140) K(30,260) C(25,400) F(45,350) I(50,275) L(60,260)
- Ranges:
Age: 0-40 40-55 ≥ 55+ Salary: 0-90K 90K-225K ≥ 225K+
-
Grid index file:
- How the grid index file
is stored:
- The text book use the
following method to
represent the
index file:
For the following data set:
(age, salary (in $1,000)) (I highlighted 2 data points) A(25,6) D(45,60) G(50,75) J(50,100) B(50,120) E(70,110) H(85,140) K(30,260) C(25,400) F(45,350) I(50,275) L(60,260)
- It is easy to
generalize the
Grid Index to
higher dimensions: