[jira] [Created] (TINKERPOP3-1013) Traverser tags as a safer way of using path labels

["Marko A. Rodriguez (JIRA)" <ji...@apache.org>]

Marko A. Rodriguez created TINKERPOP3-1013:
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             Summary: Traverser tags as a safer way of using path labels
                 Key: TINKERPOP3-1013
                 URL: https://issues.apache.org/jira/browse/TINKERPOP3-1013
             Project: TinkerPop 3
          Issue Type: Improvement
          Components: process
    Affects Versions: 3.1.0-incubating
            Reporter: Marko A. Rodriguez
             Fix For: 3.1.1-incubating


We should add the following methods to {{Traverser}}.

{code}
void Traverser.addTag(final String tag)
boolean Traverser.hasTag(final String tag)
void Traverser.dropTag(final String tag)
void Traverser.dropTags()
{code}

What is the point of a "tag" ? There are two use cases:

1. Currently {{MatchStep}} "tags" a traverser with {{traverser.getPath().addLabel(step.getId())}}.  This means that the path data of the traverser is used to store which branches of the {{match()}} the traverser has already gone down. This is a hack as now the {{travesrer.path()}} has a weird step ID label. Also, its inefficient as the path needs to be searched for the respective "tag." A {{Set<String>}} is much more efficient.

2. Intersect/symmetric difference will require some sort of "tagging" as explained in Section 4 of http://arxiv.org/abs/1511.06278. We could, of course, use the {{MatchStep}} way of doing things, but again, thats a hack.

3. When we support TINKERPOP3-736, using the "{{path()}}-hack" will not work as two branches will have different stepIds but the same tag.

In short, anytime we need to know if a particular branch of a traversal was taken, {{Traverser.getTag()}} is our friend. 

IMPORTANT: This will go into {{Traverser.Admin}} as no user should use these tags. These are simply for internal markup of traverser.



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