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nydatamind007
nydatamind007

Reputation: 21

How does Grakn compute rules when running a query for a transitive relation?

I'm working in memSQL on a project to identify certain batter pitcher relationships in the MLB; where I look at what batters had the most success against various pitchers and when. With the goal of creating a heat map of teams and lineups of a specific year(s)(collection of batters) against various groups of pitchers.

I ran into a problem trying to query for teams with a positive net score against pitchers. When looking for all Batter of a given team.

I came across Grakn and this blog post: https://blog.grakn.ai/comparing-graql-to-sql-part-2-2-745f79e9528d

Seems that I could utilise rules to then query for something like this.

Taking a stab at the rule - I want to make team performance against a pitcher based on a collection of batter performance of that same pitcher.

I wrote this query, which would just query for at-bat performance where batter is in a plays-for with a given team. However the query doesn't give me the result I am expecting?

when {
(batting: $b, pitching: $p) isa at-bat;
(playing: $b, plays-for: $t) isa team;
}, then {
(plays-for: $c, pitching: $d) isa at-bat;
};

Also does anyone knows when these rules are computed and what is the performance overhead?

Upvotes: 1

Views: 86

Answers (1)

Adam Mitchell
Adam Mitchell

Reputation: 61

Just to check quickly, are you defining the rule in your schema? Rules need to be inserted into Grakn using a define statement, since they are treated like schema elements. If you are trying to run it in-line in the query I would have thought you would get an error, but maybe that's not what you are doing and I am misunderstanding.

To answer the other question, rules are computed at query time, we detect which rules might change the outcome of a query and effectively make it a part of the query traversal, so in theory it works like a normal transitive search over a graph. In practice it's a bit different.

Upvotes: 1

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