[Pig Wiki] Update of "PigExecutionModel" by AntonioMagnaghi

[Apache Wiki <wi...@apache.org>]

Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Pig Wiki" for change notification.

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

------------------------------------------------------------------------------
     * 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___
+