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From Apache Wiki <wikidi...@apache.org>
Subject [Pig Wiki] Update of "PigExecutionModel" by AntonioMagnaghi
Date Tue, 29 Jan 2008 21:38:23 GMT
Dear Wiki user,

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The following page has been changed by AntonioMagnaghi:

     * Stream Programming Model / MIT Stream-It
        * official page for stream-it: http://www.cag.csail.mit.edu/streamit/ (Articles on
the compiler might be useful)
+ == Physical Plan Structure ==
+  1. A criterion we are adopting in the redesign of the logical and physical layer in Pig
is to promote what used to be EvalSpec’s and Cond’s to operators.
+  1. Such approach provides: 1.) a clearer definition of the language; 2.) better identification
of possibility for optimizations of various form
+  1. Logical operators are such that they provide the logical representation of a Pig computation
and type checking.
+  1. The aspects that pertain to carrying out the actual computations on a given dataset
belong to physical operators. Exploitation of type information should enable efficient computations.
+  1. The mapping from logical operators to physical operators aims at preserving isomorphism
of computation trees. Hence, most logical operators have their counterpart in physical operators.
For instance, a logical FILTER will be translated into a physical FILTER. See translation
scheme below.
+  1. These are the following exceptions:
+     1. Logical Cogroup to be translated into a Physical LocalRearrange and GlobalRearrange.
+ === Logical to Physical Translation Scheme ===
+ __FILTER___

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