Class: LD::Patch::Algebra::Path

Inherits:
SPARQL::Algebra::Operator
  • Object
show all
Includes:
SPARQL::Algebra::Evaluatable, SPARQL::Algebra::Query
Defined in:
lib/ld/patch/algebra/path.rb

Overview

The LD Patch ‘path` operator.

The Path creates a closure over path operands querying ‘queryable` for terms having a relationship with the input `terms` based on each operand. The terms extracted from the first operand are used as inputs for the next operand until a final set of terms is found. These terms are returned as `RDF:Query::Solution` bound the the variable `?path`

Returns input terms

Queries `queryable` for objects where the input terms are subjects and the predicate is `:p`

Queries `queryable` for subjects where input terms are objects and the predicate is `:p`, by executing the `reverse` operand using input terms to get a set of output terms.

Returns the input terms satisfying the constrant.

Maps terms using `(path :p)`, using them as terms for `(path :q)`, then subsets these based on the constraint.

Examples:

empty path

(path)

forward path

(path :p)

reverse path

(path (reverse :p))

constraint

(path (constraint (path) :c, 1))

chained path elements

(path :p :q (constraint (path) :c, 1))

Constant Summary collapse

NAME = 
:path

Instance Method Summary collapse

Instance Method Details

#execute(queryable, options = {}) ⇒ RDF::Query::Solutions

Executes this operator using the given variable ‘bindings` and a starting term, returning zero or more terms at the end of the path.

Parameters:

  • queryable (RDF::Queryable) —

    the graph or repository to query

  • options (Hash{Symbol => Object}) (defaults to: {}) —

    ({}) options passed from query

Options Hash (options):

  • starting (Array<RDF::Term>) —

    terms

Returns:

  • (RDF::Query::Solutions) —

    solutions with ‘:term` mapping



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# File 'lib/ld/patch/algebra/path.rb', line 47

def execute(queryable, options = {})
  solutions = RDF::Query::Solutions.new

  # Iterate updating terms, then create solutions from matched terms
  operands.inject(Array(options.fetch(:terms))) do |terms, op|
    case op
    when RDF::URI
      terms.map do |subject|
        queryable.query({subject: subject, predicate: op}).map(&:object)
      end.flatten
    when SPARQL::Algebra::Query
      # Get path solutions for each term for op
      op.execute(queryable, **options.merge(terms: terms)).map do |soln|
        soln.path
      end.flatten
    else
      raise NotImplementedError, "Unknown path operand #{op.inspect}"
    end
  end.each do |term|
    solutions << RDF::Query::Solution.new(path: term)
  end
  solutions
end