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From "Pi Song (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-320) The parser/type checker should use the getSchema method of UDFs to deduce return type/schema
Date Fri, 18 Jul 2008 15:10:31 GMT

    [ https://issues.apache.org/jira/browse/PIG-320?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12614751#action_12614751

Pi Song commented on PIG-320:

First, let's define a concrete EvalFunc semantic:-

EvalFunc: U -> T

T is hardcoded in UDF implementation but in case that T is a complex type then its schema
can be determined by U

getReturnType() should return the hardcoded type (e.g. Int, Double, Bag). outputSchema() should
return schemas of complex types (always returning null for simple types). 

I think this should be simple enough for users to understand. The most common case would be
users creating UDF: simpleType -> simpleType , they don't have to override outputSchema().

Some of the current built-in functions will be broken following this semantic but they can
be easily fixed.


> The parser/type checker should use the getSchema method of UDFs to deduce return type/schema
> --------------------------------------------------------------------------------------------
>                 Key: PIG-320
>                 URL: https://issues.apache.org/jira/browse/PIG-320
>             Project: Pig
>          Issue Type: Bug
>          Components: impl
>    Affects Versions: types_branch
>            Reporter: Santhosh Srinivasan
>            Assignee: Santhosh Srinivasan
>             Fix For: types_branch
>         Attachments: udf_outputSchema.patch
> Currently, the parser/type checker uses the getReturnType to deduce the return type of
the user defined function (UDF). This mechanism is satisfactory only for basic types (int,
long, ...); for composite types (tuple, bag), the schema is also required.The abstract class
EvalFunc interface exposes the outputSchema to deduce the return type/schema of the UDF. The
parser/type checker should use this method to figure out the return type/schema of the UDF
and use it appropriately. 

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