cayleygraph/cayley

ForAll / Universal Quantifiers

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#209 opened on Feb 9, 2015

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Description

We have a Not iterator now. It'd be possible to add a shorthand macro in Gremlin to emulate the Universal Quantifier, ForAll.

All queries currently work on existence. That is, each stage depends on "there exists some path X to node Y". Using negation you can achieve "for all paths from X, (rest of query holds)".

The key insight being that (X holds for (ForAll A)) == (X holds for A) AND (X holds for (Not (Not A))) == (X holds for (A AND (Not (Not A))))

In today's parlance, this is: var a = g.M().... g.V().And(a).And(g.V().Except(g.V().Except(a)))...

It's a hack, but one that holds mathematically. Currently can be implemented as a macro on the query level, and is actually really hard to optimize further. (Suggestions, of course, are welcome)

Contributor guide

Research direction
Implement the ForAll macro by combining existing Not, And, and Except steps. Use the mathematical identity: ForAll(A, X) == And(X, Not(Not(X))) applied to all paths from A.
Tech stack
go
Domain
backenddatabase
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Gograph databasesGremlin
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50