class SPARQL::Algebra::Operator::Join
The SPARQL
GraphPattern `join` operator.
@example
(prefix ((: <http://example/>)) (join (bgp (triple ?s ?p ?o)) (graph ?g (bgp (triple ?s ?q ?v)))))
Constants
- NAME
Public Instance Methods
Executes each operand with `queryable` and performs the `join` operation by creating a new solution set containing the `merge` of all solutions from each set that are `compatible` with each other.
@param [RDF::Queryable] queryable
the graph or repository to query
@param [Hash{Symbol => Object}] options
any additional keyword options
@yield [solution]
each matching solution
@yieldparam [RDF::Query::Solution] solution @yieldreturn [void] ignored @return [RDF::Query::Solutions]
the resulting solution sequence
@see www.w3.org/TR/sparql11-query/#sparqlAlgebra @see www.rubydoc.info/github/ruby-rdf/rdf/RDF/Query/Solution#merge-instance_method @see www.rubydoc.info/github/ruby-rdf/rdf/RDF/Query/Solution#compatible%3F-instance_method
# File lib/sparql/algebra/operator/join.rb, line 37 def execute(queryable, **options, &block) # Join(Ω1, Ω2) = { merge(μ1, μ2) | μ1 in Ω1 and μ2 in Ω2, and μ1 and μ2 are compatible } # eval(D(G), Join(P1, P2)) = Join(eval(D(G), P1), eval(D(G), P2)) # # Generate solutions independently, merge based on solution compatibility debug(options) {"Join #{operands.to_sse}"} left = queryable.query(operand(0), depth: options[:depth].to_i + 1, **options) debug(options) {"(join)=>(left) #{left.map(&:to_h).to_sse}"} right = queryable.query(operand(1), depth: options[:depth].to_i + 1, **options) debug(options) {"(join)=>(right) #{right.map(&:to_h).to_sse}"} @solutions = RDF::Query::Solutions(left.map do |s1| right.map { |s2| s2.merge(s1) if s2.compatible?(s1) } end.flatten.compact) debug(options) {"(join)=> #{@solutions.map(&:to_h).to_sse}"} @solutions.each(&block) if block_given? @solutions end
Optimizes this query.
Groups of one graph pattern (not a filter) become join(Z, A) and can be replaced by A. The empty graph pattern Z is the identity for join:
Replace join(Z, A) by A Replace join(A, Z) by A
@return [Join, RDF::Query] `self` @return [self] @see SPARQL::Algebra::Expression#optimize!
# File lib/sparql/algebra/operator/join.rb, line 80 def optimize!(**options) ops = operands.map {|o| o.optimize(**options) }.select {|o| o.respond_to?(:empty?) && !o.empty?} @operands = ops self end
The same blank node label cannot be used in two different basic graph patterns in the same query
SPARQL::Algebra::Operator#validate!
# File lib/sparql/algebra/operator/join.rb, line 59 def validate! left_nodes, right_nodes = operand(0).ndvars, operand(1).ndvars unless (left_nodes.compact & right_nodes.compact).empty? raise ArgumentError, "sub-operands share non-distinguished variables: #{(left_nodes.compact & right_nodes.compact).to_sse}" end super end