[jira] [Commented] (AIRFLOW-5268) Rectify DAG naming conventions

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/AIRFLOW-5268?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16911640#comment-16911640 ] 

ASF GitHub Bot commented on AIRFLOW-5268:
-----------------------------------------

BasPH commented on pull request #5874: [AIRFLOW-5268] Apply same DAG naming conventions as in literature
URL: https://github.com/apache/airflow/pull/5874
 
 
   Make sure you have checked _all_ steps below.
   
   ### Jira
   
   - [x] My PR addresses the following [Airflow Jira](https://issues.apache.org/jira/browse/AIRFLOW/) issues and references them in the PR title. For example, "\[AIRFLOW-XXX\] My Airflow PR"
     - https://issues.apache.org/jira/browse/AIRFLOW-5268
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   ### Description
   
   - [x] Here are some details about my PR, including screenshots of any UI changes:
   
   The Airflow codebase is extremely confusing because the concept "root" node in Airflow is actually the last, finishing node of a DAG, while in DAG literature root nodes are the first nodes to execute. Or, as literature also explains it: root nodes are nodes without upstream dependencies, while it was implemented as nodes without downstream dependencies.
   
   This PR aligns the Airflow implementation of a "root" node with DAG literature. I've also implemented a `leaves` property to make a clear distinction between first/starting nodes and last/finishing nodes. Also, to my surprise there weren't even tests for these basic properties, so I added 3 tests verifying the behaviour of `roots` and `leaves`.
   
   The implementation involved:
   - Correctly implementing the definition root and leaf nodes
   - Adding tests verifying this behaviour
   - Some switching between upstream/downstream calls here and there because of the now correct behaviour
   
   ### Tests
   
   - [x] My PR adds the following unit tests __OR__ does not need testing for this extremely good reason:
   
   Added 3 tests, see above.
   
   ### Commits
   
   - [ ] My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "[How to write a good git commit message](http://chris.beams.io/posts/git-commit/)":
     1. Subject is separated from body by a blank line
     1. Subject is limited to 50 characters (not including Jira issue reference)
     1. Subject does not end with a period
     1. Subject uses the imperative mood ("add", not "adding")
     1. Body wraps at 72 characters
     1. Body explains "what" and "why", not "how"
   
   ### Documentation
   
   - [ ] In case of new functionality, my PR adds documentation that describes how to use it.
     - All the public functions and the classes in the PR contain docstrings that explain what it does
     - If you implement backwards incompatible changes, please leave a note in the [Updating.md](https://github.com/apache/airflow/blob/master/UPDATING.md) so we can assign it to a appropriate release
   
   ### Code Quality
   
   - [ ] Passes `flake8`
   
 
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> Rectify DAG naming conventions
> ------------------------------
>
>                 Key: AIRFLOW-5268
>                 URL: https://issues.apache.org/jira/browse/AIRFLOW-5268
>             Project: Apache Airflow
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 2.0.0, 1.10.5
>            Reporter: Bas Harenslak
>            Priority: Major
>




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