Package org.aksw.jenax.analytics.core

Interface RootedQuery

All Known Implementing Classes:
RootedQueryFromPartitionedQuery1, RootedQueryImpl
public interface RootedQuery
A wrapper for a partitioned query where a single node of its template is designated as a root node. This enables construction of Resource instances even from partitions based on multiple partition variables. For example, facet value counts can be conceptually expressed in the following extended SPARQL syntax: 
 
   CONSTRUCT { _:b :facet ?f; :facetValue ?fv ; :facetValueCount ?fvc }
     { SELECT ?f ?fv (COUNT(DISTINCT *) AS ?fvc) { ... } GROUP BY ?f ?fv}
   PARTITION BY ?f ?fv
   ROOT _:b
Evaluation of partitioned queries remaps blank nodes of the template only ONCE per partition. In this example, for each distinct binding of ?f and ?fv the blank node _:b will be mapped to a single fresh blank node for each partition. As a consequence, in the example, the computed count ONLY applies to a certain binding of both ?f and ?fv. There does not exist a resource the count can be attached to as a property, though one can be allocated using: 
   BIND(CONCAT('http://...', STR(?f), STR(?vf)) AS ?grouped)
However, this allocation is usually not very useful:
  • Query rewriting that filters on ?grouped is inefficient as it can not exploit any index
  • As ?grouped is derived from ?f and ?fv it duplicates their information which consequently needlessly increases the result set size and thus lowers performance of transmitting it.
Author:
raven

  • Method Summary

    Modifier and Type
    Method
    Description
    ObjectQuery
    getObjectQuery()
     
    org.apache.jena.graph.Node
    getRootNode()
    The designated root node.

  • Method Details

    • getRootNode

      org.apache.jena.graph.Node getRootNode()
      The designated root node. The following rules apply:
      • If getObjectQuery().getTemplate() is non-empty then the root node should be mentioned in the template.
      • In case the template is empty then the root node should be a variable that occurs in getObjectQuery().getRelation().getElement(). Furthermore, if in this case the query is partitioned by a single variable then the root node should match that one.
      Returns:

    • getObjectQuery

      ObjectQuery getObjectQuery()