pigLatin中"外袋"和"内袋"的区别是什么？

Question

手册/文档广泛使用'inner bag'和'outer bag'的语言(例如:http://pig.apache.org/docs/r0.11.1/basic.html ),但我还没能明确指出分离条款的确切定义.

例如,所有内在相互关联的:

• 如果我给你一个包'foo',你需要知道什么才能将foo标记为'内袋'与'外袋'？
• "任何包包"谁不是最外层的包包然后是"内袋"？
• 内部和外部的标签总是独占吗？
• 在PigLatin中,所有"袋子"关系" - 或者只是'最外层袋'的关系？(和内袋不是关系)

创建一个可讨论的例子:

grunt> dump A;      
(1,2,3)
(4,2,1)
(8,3,4)
(4,3,3)


grunt> W1 = GROUP A   ALL;         
grunt> W2 = GROUP W1  ALL;
grunt> W3 = GROUP W2  ALL;
grunt> W4 = GROUP W3  ALL;

grunt> describe W4;
W4: {group: chararray,W3: {(group: chararray,W2: {(group: chararray,W1: {(group: chararray,A: {(f1: int,f2: int,f3: int)})})})}}


grunt> illustrate W4;
(1,2,3)
---------------------------------------------------
| A     | f1:int      | f2:int      | f3:int      | 
---------------------------------------------------
|       | 1           | 2           | 3           | 
|       | 8           | 3           | 4           | 
---------------------------------------------------
------------------------------------------------------------------------------------------------
| W1     | group:chararray      | A:bag{:tuple(f1:int,f2:int,f3:int)}                          | 
------------------------------------------------------------------------------------------------
|        | all                  | {(1, 2, 3), (8, 3, 4)}                                       | 
------------------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------------------------------------------------------------
| W2     | group:chararray      | W1:bag{:tuple(group:chararray,A:bag{:tuple(f1:int,f2:int,f3:int)})}                                         | 
-----------------------------------------------------------------------------------------------------------------------------------------------
|        | all                  | {(all, {(1, 2, 3), (8, 3, 4)})}                                                                             | 
-----------------------------------------------------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| W3     | group:chararray      | W2:bag{:tuple(group:chararray,W1:bag{:tuple(group:chararray,A:bag{:tuple(f1:int,f2:int,f3:int)})})}                                                        | 
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|        | all                  | {(all, {(all, {(1, 2, 3), (8, 3, 4)})})}                                                                                                                   | 
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| W4     | group:chararray      | W3:bag{:tuple(group:chararray,W2:bag{:tuple(group:chararray,W1:bag{:tuple(group:chararray,A:bag{:tuple(f1:int,f2:int,f3:int)})})})}                                                                       | 
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|        | all                  | {(all, {(all, {(all, {(1, 2, 3), (8, 3, 4)})})})}                                                                                                                                                         | 
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

grunt> dump W4;
(all,{(all,{(all,{(all,{(1,2,3),(4,2,1),(8,3,4),(4,3,3)})})})})

袋子里面 - W1,W2,W3,W4--哪个是内层,哪个是外层？

Answer 1

外袋其实是有关系的A。这有点奇怪，但是一旦您知道什么是内袋，就会清楚了。我们来看看W1，因为嵌套袋不会改变答案。

架构和输出W1：

W1: {group:chararray, A:bag{:tuple(f1:int,f2:int,f3:int)}}
(all,{(1, 2, 3), (8, 3, 4)})

W1我们可以看到他们是named中的一个字段A中的一个字段，它是一个包。这是一个内部包，因为该包是关系中的一个字段。

请记住，bags 只是无序的元组集合，我们可以看到这是 的输出W1。现在，看看关系的输出A：

(1,2,3)
(4,2,1)
(8,3,4)
(4,3,3)

Pig 不保证这些元组的顺序（除非你ORDER什么的）。所以，如果你仔细想想，关系A实际上只是一组无序的元组。这是一个外袋。

您可以在此处找到一些相关示例。