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From "Alan Gates (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-158) Rework logical plan
Date Mon, 24 Mar 2008 02:07:24 GMT

    [ https://issues.apache.org/jira/browse/PIG-158?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12581456#action_12581456
] 

Alan Gates commented on PIG-158:
--------------------------------

A comment on Pi's question

>>1) How do you maintain relations between LOs and dependencies in the abstract graph
layer (OperatorPlan) in the same time?<<

An issue we have with the logical plan is some operators have two kinds of inputs, relational
operator inputs and expression operator inputs.  Take filter as an example.  It has a predecessor
operator, which will be a relational operator (load, foreach, etc.)  It also has an expression
operator, it's condition.  We have, for the moment, opted to model that as relational operator
connections are edges in the LogicalPlan, while expression operator connections are made explicit
in the code.  So, LOFilter has an ExpressionOperator mCond member that tracks its conditional,
but it relies on LogicalPlan to maintain its connection to its predecessor relational operator.

We have to do something like this because classes like filters need to be able to keep track
of the semantic difference between their different inputs.  We could modify it so that expression
operator inputs are still tracked in the logical plan.  This would make visiting easier, as
all connection would be modeled in the graph.  Perhaps this is a good idea.  But LOFilter
will still have to remember which connection is its conditional.  Thoughts?

> 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
>
>
> Rework the logical plan in line with http://wiki.apache.org/pig/PigExecutionModel

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