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The following page has been changed by AntonioMagnaghi:
http://wiki.apache.org/pig/PigExecutionModel

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     * 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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