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https://issues.apache.org/jira/browse/TINKERPOP3-700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14582191#comment-14582191
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Marko A. Rodriguez commented on TINKERPOP3-700:
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I just added {{Path.getSingle(pop,label)}} and {{Path.getList(label)}}. Right
now they are default methods in {{Path}} and {{PathTest}} ensures they
implement the semantics correctly. If you would, can you make more efficient
implementations in {{ImmutablePath}} and {{MutablePath}}. Should be pretty easy
to do. Also, if you want to JavaDoc the methods :).
https://github.com/apache/incubator-tinkerpop/blob/1d576d88e233eb5c850fd19f67229f20bd707901/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/Path.java#L100-L118
> WhereStep should "MatchStep" and ConjunctionP should use the BudgetAlgorithm
> ----------------------------------------------------------------------------
>
> Key: TINKERPOP3-700
> URL: https://issues.apache.org/jira/browse/TINKERPOP3-700
> Project: TinkerPop 3
> Issue Type: Improvement
> Components: process
> Reporter: Marko A. Rodriguez
>
> {code}
> g.V.as('a').where(a.knows.b
> a.knows.c
> b.knows.c)
> {code}
> The above can be written as an OrP of the form:
> {code}
> g.V.as('a').or(select(a).knows.b.select(b).knows.c.select(a).knows.where(eq(c)),
>
> select(a).knows.c.select(a).knows.b.select(b).knows.where(eq(c)));
> {code}
> In essence, the where-statements are rewritten in terms of every possible
> permutation. When these permutations are put into an OrP (via
> or(traversals…)), then if any branch returns a result, then the original 'a'
> is emitted (as {{WhereStep}} is a {{FilterStep}}). If {{OrP}} is under the
> BudgetAlgorithm, then {{OrP}} will "thread between" its traversals until a
> value is yielded. *And given that all permutations are the same semantics --
> if one fails, they all fail!*
> What is nice about this, is that arbitrary nesting comes "for free."
> {code}
> g.V.as('a').where(a.knows.b
> a.uncle.b
> and(a.worksFor.c
> b.worksFor.c))
> {code}
> This is rewritten as:
> {code}
> g.V.as('a').or(select(a).knows.b.or(select(a).worksFor.c.select(b).worksFor.where(eq(c)),select(b).worksFor.c.select(a).worksFor.where(eq(c))).select(a).uncle.where(eq(b)),
>
> select(a).uncle.b.select(a).knows.where(eq(b)).or(select(a).worksFor.c.select(b).worksFor.where(eq(c)),select(b).worksFor.c.select(a).worksFor.where(eq(c))))
> {code}
> *IMPORTANT* This is not a "match" in the {{MatchStep}} sense as it doesn't
> return all permutations that bind, it only filters based on a single match.
> What is interesting about this approach:
> 1. The rewrite algorithm seems simple as its just concatenation given
> {{select()}}-projections and {{where(eq)}}-tails.
> 2. The cool thing about the rewrite in all possible permutations is that if
> any one {{FastNoSuchElementException}}, its booted from the {{ConjunctionP}}
> analysis.
> 3. {{ConjunctionP}} has the BudgetAlgorithm and thus can be used for ANY
> step that has conjunctions -- {{HasStep}}, {{IsStep}}, etc.
> 4. It uses the path data structure to maintain the variable bindings.
> {{WhereStep}} has no state! Its all about {{OrP}}.
> 5. Given that the path data is the variable bindings, then this also works
> for OLAP as the traverser contains all the information it needs (no central
> location of analysis!)
> - However, you would only pick one permutation to do as `or()` does not
> exist in OLAP.
> - and with one permutation, {{where().select()}} is then {{MatchStep}}
> which would then work in OLAP!
> - thus, Gremlin OLAP can rewrite {{match()}} to the
> {{where().select()}} form and TADA!
>
> *IMPORTANT* 4 and 5 above are pretty insane consequences. And if any, we
> should at least use this realization to make {{match()}} work in OLAP.
> Next, realize that how {{where()}} should work is that if an {{as()}} is NOT
> in the path data structure, then its a variable bindings for rewrite.
> Moreover, if you don't provide a start {{as()}}, it is assumed to be the
> incoming object (currently how {{where()}} works). For example:
> {code}
> g.V.where(knows.b
> knows.c
> b.knows.c)
> {code}
> This is rewritten as:
> {code}
> g.V.or(x.select(x).knows.b.or(select(b).worksFor.where(eq(a)),select(x).worksFor.where(eq(b))).select(x).uncle.where(eq(b)),
>
> x.select(x).uncle.b.select(x).knows.where(eq(b)).or(select(b).worksFor.where(eq(x)),select(x).worksFor.where(eq(b))))
>
> {code}
> To be sure, the {{as('a').select('a')}} fragments can of course be optimized
> out to just {{as('a')}}.
>
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