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From "Pi Song (JIRA)" <j...@apache.org>
Subject [jira] Created: (PIG-143) Proposal for refactoring of parsing logic in Pig
Date Fri, 07 Mar 2008 23:17:46 GMT
Proposal for refactoring of parsing logic in Pig

                 Key: PIG-143
                 URL: https://issues.apache.org/jira/browse/PIG-143
             Project: Pig
          Issue Type: Improvement
            Reporter: Pi Song
            Assignee: Pi Song

This is  a place holder for me to come up with a complete proposal. In the mean time, I definitely
need your opinions!!!

The basic concept is that now we do validation logic in parsing stage (for example, file existence
checking) which I think is not clean and difficult to add new validation rules.

The way I propose briefly:-
- Only keep parsing logic in the parser and leave output of parsing logic being unchecked
logical plans.
- Create a new class called LogicalPlanValidatorManager which is responsible for validation
- A new validation logic will be subclassing LogicalPlanValidator
- We can implement chaining of LogicalPlanValidator inside LogicalPlanValidatorManager to
allow new LogicalPlanValidator to be added easily. When plugging in new logic, we do it here.
Therefore a new LogicalPlanValidator can be implemented like a plug-in.

Here is a list of possible LogicalPlanValidators in my mind (Please add what you want):- 
- The first LogicalPlanValidator to be implemented is FileExistence validator which is from
the current logic we have.
- Second LogicalPlanValidator is to sort out filename conflict (At the moment you can save/load
same file over and over again in the same plan, this is very confusing. Possibly we should
not allow same file name in any single plan?)
- Meta data checking + type system checking as mentioned in Pig-142

The common way to implement a LogicalPlanValidator is based on Visitor pattern. Whether this
is universal for all cases or not, I need to think through more.

The merit of implementing this proposal will be based on the number of validation rules we
actually need. If we don't have so many things to check, it will become just a nice feature
that doesn't have much value. However, I believe at least it will make the parsing logic cleaner.

This proposal only applies to the LogicalPlan. For PhysicalPlan, where validation logics (backend
specific) are required. The same concept can be applied.

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