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From "Pradeep Kamath" <prade...@yahoo-inc.com>
Subject RE: two-level access problem?
Date Tue, 03 Nov 2009 19:10:09 GMT
>From comments in Schema.java:
    // In bags which have a schema with a tuple which contains
    // the fields present in it, if we access the second field (say)
    // we are actually trying to access the second field in the
    // tuple in the bag. This is currently true for two cases:
    // 1) bag constants - the schema of bag constant has a tuple
    // which internally has the actual elements
    // 2) When bags are loaded from input data, if the user 
    // specifies a schema with the "bag" type, he has to specify
    // the bag as containing a tuple with the actual elements in 
    // the schema declaration. However in both the cases above,
    // the user can still say b.i where b is the bag and i is 
    // an element in the bag's tuple schema. So in these cases,
    // the access should translate to a lookup for "i" in the 
    // tuple schema present in the bag. To indicate this, the
    // flag below is used. It is false by default because, 
    // currently we use bag as the type for relations. However 
    // the schema of a relation does NOT have a tuple fieldschema
    // with items in it. Instead, the schema directly has the 
    // field schema of the items. So for a relation "b", the 
    // above b.i access would be a direct single level access
    // of i in b's schema. This is treated as the "default" case
    private boolean twoLevelAccessRequired = false;

-----Original Message-----
From: Dmitriy Ryaboy [mailto:dvryaboy@gmail.com] 
Sent: Monday, November 02, 2009 5:33 PM
To: pig-dev@hadoop.apache.org
Subject: two-level access problem?

Could someone explain the nature of the "two-level access problem"
referred to in the Load/Store redesign wiki and in the DataType code?


Thanks,
-D

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