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https://issues.apache.org/jira/browse/FLINK-2398?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14701491#comment-14701491
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ASF GitHub Bot commented on FLINK-2398:
---------------------------------------

Github user aljoscha commented on the pull request:

    https://github.com/apache/flink/pull/988#issuecomment-132260208
  
    I think this is good now. I adapted the Streaming Tests to always use 
`StreamingMultipleProgramTestBase` when appropriate. The earlier problems where 
caused by some tests using 
`StreamingExecutionEnvironment.getExecutionEnvironment()` without being in a 
class that is derived from `StreamingMultipleProgramTestBase`. This caused 
those tests to pick up the used environment from another test when run on 
travis. (In an IDE the tests would just use a LocalEnvironment because no other 
environment would be set.)


> Decouple StreamGraph Building from the API
> ------------------------------------------
>
>                 Key: FLINK-2398
>                 URL: https://issues.apache.org/jira/browse/FLINK-2398
>             Project: Flink
>          Issue Type: Improvement
>          Components: Streaming
>            Reporter: Aljoscha Krettek
>            Assignee: Aljoscha Krettek
>
> Currently, the building of the StreamGraph is very intertwined with the API 
> methods. DataStream knows about the StreamGraph and keeps track of splitting, 
> selected names, unions and so on. This leads to the problem that is is very 
> hard to understand how the StreamGraph is built because the code that does it 
> is all over the place. This also makes it hard to extend/change parts of the 
> Streaming system.
> I propose to introduce "Transformations". A transformation hold information 
> about one operation: The input streams, types, names, operator and so on. An 
> API method creates a transformation instead of fiddling with the StreamGraph 
> directly. A new component, the StreamGraphGenerator creates a StreamGraph 
> from the tree of transformations that result from program specification using 
> the API methods. This would relieve DataStream from knowing about the 
> StreamGraph and makes unions, splitting, selection visible transformations 
> instead of being scattered across the different API classes as fields.



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