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290 lines
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Plaintext
290 lines
8.0 KiB
Plaintext
This directory contains the code for the user-defined type,
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CUBE, representing multidimensional cubes.
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FILES
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-----
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Makefile building instructions for the shared library
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README.cube the file you are now reading
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buffer.c globals and buffer access utilities shared between
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the parser (cubeparse.y) and the scanner (cubescan.l)
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buffer.h function prototypes for buffer.c
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cube.c the implementation of this data type in c
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cube.sql.in SQL code needed to register this type with postgres
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(transformed to cube.sql by make)
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cubedata.h the data structure used to store the cubes
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cubeparse.y the grammar file for the parser (used by cube_in() in cube.c)
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cubescan.l scanner rules (used by cube_yyparse() in cubeparse.y)
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INSTALLATION
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============
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To install the type, run
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make
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make install
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For this to work, make sure that:
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. the cube source directory is in the postgres contrib directory
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. the user running "make install" has postgres administrative authority
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. this user's environment defines the PGLIB and PGDATA variables and has
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postgres binaries in the PATH.
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This only installs the type implementation and documentation. To make the
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type available in any particular database, do
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psql -d databasename < cube.sql
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If you install the type in the template1 database, all subsequently created
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databases will inherit it.
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To test the new type, after "make install" do
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make installcheck
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If it fails, examine the file regression.diffs to find out the reason (the
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test code is a direct adaptation of the regression tests from the main
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source tree).
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SYNTAX
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======
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The following are valid external representations for the CUBE type:
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'x' A floating point value representing
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a one-dimensional point or one-dimensional
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zero length cubement
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'(x)' Same as above
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'x1,x2,x3,...,xn' A point in n-dimensional space,
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represented internally as a zero volume box
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'(x1,x2,x3,...,xn)' Same as above
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'(x),(y)' 1-D cubement starting at x and ending at y
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or vice versa; the order does not matter
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'(x1,...,xn),(y1,...,yn)' n-dimensional box represented by
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a pair of its opposite corners, no matter which.
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Functions take care of swapping to achieve
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"lower left -- upper right" representation
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before computing any values
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Grammar
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-------
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rule 1 box -> O_BRACKET paren_list COMMA paren_list C_BRACKET
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rule 2 box -> paren_list COMMA paren_list
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rule 3 box -> paren_list
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rule 4 box -> list
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rule 5 paren_list -> O_PAREN list C_PAREN
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rule 6 list -> FLOAT
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rule 7 list -> list COMMA FLOAT
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Tokens
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------
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n [0-9]+
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integer [+-]?{n}
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real [+-]?({n}\.{n}?)|(\.{n})
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FLOAT ({integer}|{real})([eE]{integer})?
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O_BRACKET \[
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C_BRACKET \]
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O_PAREN \(
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C_PAREN \)
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COMMA \,
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Examples of valid CUBE representations:
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--------------------------------------
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'x' A floating point value representing
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a one-dimensional point (or, zero-length
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one-dimensional interval)
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'(x)' Same as above
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'x1,x2,x3,...,xn' A point in n-dimensional space,
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represented internally as a zero volume cube
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'(x1,x2,x3,...,xn)' Same as above
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'(x),(y)' A 1-D interval starting at x and ending at y
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or vice versa; the order does not matter
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'[(x),(y)]' Same as above
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'(x1,...,xn),(y1,...,yn)' An n-dimensional box represented by
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a pair of its diagonally opposite corners,
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regardless of order. Swapping is provided
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by all comarison routines to ensure the
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"lower left -- upper right" representation
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before actaul comparison takes place.
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'[(x1,...,xn),(y1,...,yn)]' Same as above
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White space is ignored, so '[(x),(y)]' can be: '[ ( x ), ( y ) ]'
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DEFAULTS
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========
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I believe this union:
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select cube_union('(0,5,2),(2,3,1)','0');
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cube_union
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-------------------
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(0, 0, 0),(2, 5, 2)
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(1 row)
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does not contradict to the common sense, neither does the intersection
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select cube_inter('(0,-1),(1,1)','(-2),(2)');
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cube_inter
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-------------
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(0, 0),(1, 0)
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(1 row)
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In all binary operations on differently sized boxes, I assume the smaller
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one to be a cartesian projection, i. e., having zeroes in place of coordinates
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omitted in the string representation. The above examples are equivalent to:
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cube_union('(0,5,2),(2,3,1)','(0,0,0),(0,0,0)');
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cube_inter('(0,-1),(1,1)','(-2,0),(2,0)');
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The following containment predicate uses the point syntax,
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while in fact the second argument is internally represented by a box.
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This syntax makes it unnecessary to define the special Point type
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and functions for (box,point) predicates.
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select cube_contains('(0,0),(1,1)', '0.5,0.5');
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cube_contains
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--------------
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t
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(1 row)
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PRECISION
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=========
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Values are stored internally as 32-bit floating point numbers. This means that
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numbers with more than 7 significant digits will be truncated.
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USAGE
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=====
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The access method for CUBE is a GiST (gist_cube_ops), which is a
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generalization of R-tree. GiSTs allow the postgres implementation of
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R-tree, originally encoded to support 2-D geometric types such as
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boxes and polygons, to be used with any data type whose data domain
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can be partitioned using the concepts of containment, intersection and
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equality. In other words, everything that can intersect or contain
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its own kind can be indexed with a GiST. That includes, among other
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things, all geometric data types, regardless of their dimensionality
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(see also contrib/seg).
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The operators supported by the GiST access method include:
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[a, b] << [c, d] Is left of
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The left operand, [a, b], occurs entirely to the left of the
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right operand, [c, d], on the axis (-inf, inf). It means,
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[a, b] << [c, d] is true if b < c and false otherwise
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[a, b] >> [c, d] Is right of
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[a, b] is occurs entirely to the right of [c, d].
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[a, b] >> [c, d] is true if b > c and false otherwise
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[a, b] &< [c, d] Over left
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The cubement [a, b] overlaps the cubement [c, d] in such a way
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that a <= c <= b and b <= d
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[a, b] &> [c, d] Over right
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The cubement [a, b] overlaps the cubement [c, d] in such a way
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that a > c and b <= c <= d
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[a, b] = [c, d] Same as
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The cubements [a, b] and [c, d] are identical, that is, a == b
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and c == d
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[a, b] @ [c, d] Contains
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The cubement [a, b] contains the cubement [c, d], that is,
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a <= c and b >= d
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[a, b] @ [c, d] Contained in
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The cubement [a, b] is contained in [c, d], that is,
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a >= c and b <= d
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Although the mnemonics of the following operators is questionable, I
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preserved them to maintain visual consistency with other geometric
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data types defined in Postgres.
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Other operators:
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[a, b] < [c, d] Less than
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[a, b] > [c, d] Greater than
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These operators do not make a lot of sense for any practical
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purpose but sorting. These operators first compare (a) to (c),
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and if these are equal, compare (b) to (d). That accounts for
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reasonably good sorting in most cases, which is useful if
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you want to use ORDER BY with this type
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There are a few other potentially useful functions defined in cube.c
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that vanished from the schema because I stopped using them. Some of
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these were meant to support type casting. Let me know if I was wrong:
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I will then add them back to the schema. I would also appreciate
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other ideas that would enhance the type and make it more useful.
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For examples of usage, see sql/cube.sql
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CREDITS
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=======
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This code is essentially based on the example written for
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Illustra, http://garcia.me.berkeley.edu/~adong/rtree
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My thanks are primarily to Prof. Joe Hellerstein
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(http://db.cs.berkeley.edu/~jmh/) for elucidating the gist of the GiST
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(http://gist.cs.berkeley.edu/), and to his former student, Andy Dong
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(http://best.me.berkeley.edu/~adong/), for his exemplar.
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I am also grateful to all postgres developers, present and past, for enabling
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myself to create my own world and live undisturbed in it. And I would like to
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acknowledge my gratitude to Argonne Lab and to the U.S. Department of Energy
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for the years of faithful support of my database research.
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------------------------------------------------------------------------
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Gene Selkov, Jr.
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Computational Scientist
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Mathematics and Computer Science Division
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Argonne National Laboratory
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9700 S Cass Ave.
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Building 221
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Argonne, IL 60439-4844
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selkovjr@mcs.anl.gov
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