Querying the transitive closure of a predicate

Users
1

Hello,

As an example take the SKOS data model for creating thesauri. It defines the exactMatch predicate to be transitive.

Given triples:

<A> <skos:exactMatch> <B>
<B> <skos:exactMatch> <C>
<B> <skos:exactMatch> <D>

One could query for all nodes connected to <A> through one or more transitive <skos:exactMatch> predicates. This would yield:

<A> <skos:exactMatch> <B>
<A> <skos:exactMatch> <C>
<A> <skos:exactMatch> <D>

In SPARQL 1.1 this can be accomplished through property paths.

For example:

prefix skos: <http://www.w3.org/2004/02/skos/core#>

CONSTRUCT {
    <a> skos:exactMatch ?o .
}
WHERE {
    <a> skos:exactMatch+ ?o .
}

This would build all triples at least one <skos:exactMatch> away from <a>.

Can this be accomplished in any way with dgraph at the moment? Will work on shortest path enable this type of query?

Thanks,

Tony

2

Hi @abargnesi,

You can query this like so:

{
  me(id: a) {
    skos:exactMatch {
      skos:exactMatch { .. and so on .. }
    }
  }
}

This way you can find all connections to <a> which are connected via the exactMatch predicate, but multiple levels away from <a>.

Dgraph is really fast for such traversals. So, we don’t have any feature to do “path shortening.”

3

Thanks @mrjn.

In my case I do not know a priori how many edges away to search, so a finite number of steps wouldn’t work for my use case (i.e. the exact number of predicates connecting equivalent nodes).

Providing skos:exactMatch+ would find the complete transitive closure without needing to specify some arbitrary number.

4

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