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From "Santhosh Srinivasan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-158) Rework logical plan
Date Mon, 31 Mar 2008 21:54:24 GMT

    [ https://issues.apache.org/jira/browse/PIG-158?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12583896#action_12583896
] 

Santhosh Srinivasan commented on PIG-158:
-----------------------------------------

During the course of changing the parser to use the new logical operators, I encountered the
following problem. Since expression operators extend logical operators, the expression operators
require a logical plan to be associated with . In the logical plan, we will now have expression
operators that do not have any predecessors and thus becoming root nodes. Conceptually, the
expression operators are part of the relational operators and should never be root nodes in
the logical plan.

This leads us back to the original discussion about separation of relational operators and
expression operators. At this point, separation of the two kinds of operators looks like the
right choice, i.e., composition over inheritance.


Implications:

1. Move out the expression operators to Logical Expressions

2. A new visitor to visit the logical expressions

3. The Logical Operator Visitor, LOVisitor will now have an instance of Logical Expression
Visitor (LEVisitor) as a member variable. This will facilitate visiting expressions that are
part of the relational operators. Shravan, has adopted this approach for the physical operators
and expressions.

It would be nice to hear comments/thoughts.

Santhosh

> Rework logical plan
> -------------------
>
>                 Key: PIG-158
>                 URL: https://issues.apache.org/jira/browse/PIG-158
>             Project: Pig
>          Issue Type: Sub-task
>          Components: impl
>            Reporter: Alan Gates
>            Assignee: Alan Gates
>         Attachments: logical_operators.patch, logical_operators_rev_1.patch, logical_operators_rev_2.patch,
logical_operators_rev_3.patch
>
>
> Rework the logical plan in line with http://wiki.apache.org/pig/PigExecutionModel

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