Class: Sc::Fragment

Inherits:
Object
  • Object
show all
Includes:
RDF::NodeProxy
Defined in:
lib/scrappy/extractor/fragment.rb

Instance Method Summary collapse

Instance Method Details

#all_mappings(options = {}) ⇒ Object

Returns all mappings of a fragment by recursively processing all submappings.



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# File 'lib/scrappy/extractor/fragment.rb', line 13

def all_mappings options={}
  # Extracts all the mappings and any subfragment
  mappings(options).map do |mapping|
    node         = mapping[:node]
    subfragments = mapping[:subfragments]
    doc          = mapping[:doc]

    # Process subfragments
    consistent = true
    subfragments.each do |subfragment|
      # Get subfragment object
      subfragment = subfragment.proxy Node('sc:Fragment')
      
      # Add triples from submappings
      submappings = subfragment.all_mappings(options.merge(:doc=>doc))

      # Add relations
      submappings.each do |submapping|
        subnode = submapping[:node]
        node.graph << subnode if subnode.is_a?(RDF::Node)
        subfragment.sc::relation.each { |relation| node[relation] += [subnode] }
      end
      
      # Check consistency
      consistent = false if subfragment.sc::min_cardinality.first and submappings.size < subfragment.sc::min_cardinality.first.to_i
      consistent = false if subfragment.sc::max_cardinality.first and submappings.size > subfragment.sc::max_cardinality.first.to_i
    end

    # Skip the node if it has inconsistent relations
    # For example: extracting a sioc:Post with no dc:title would
    # violate the constraint sc:min_cardinality = 1
    next if !consistent
    
    { :node=>node, :subfragments=>subfragments, :doc=>doc }
  end.compact
end

#extract(options = {}) ⇒ Object

Extracts data out of a document and returns an array of nodes



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# File 'lib/scrappy/extractor/fragment.rb', line 7

def extract options={}
  all_mappings(options).map { |mapping| mapping[:node] }
end

#mappings(options) ⇒ Object

Returns the mappings between this fragment and the RDF nodes it matches



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# File 'lib/scrappy/extractor/fragment.rb', line 52

def mappings options
  # Identify the fragment's mappings
  docs = sc::selector.map { |s| graph.node(s).select options[:doc] }.flatten

  # Generate a result for each page mapping
  docs.map do |doc|
    # Build RDF nodes from identifier selectors (if present)
    node = build_node(doc, options[:referenceable])
    
    # Skip the node if no URI or bnode is created
    next if !node
    
    # Add info to the node

    # Build the object -- it can be a node or a literal
    object = if sc::type.include?(Node('rdf:Literal'))
      if options[:referenceable]
        node.rdf::value = doc[:value]
        node.rdf::type += [Node('rdf:Literal')]
        node
      else
        doc[:value]
      end
    else
      # Add statements about the node
      sc::type.each       { |type|       node.rdf::type += [type] if type != Node('rdf:Resource') }
      sc::superclass.each { |superclass| node.rdfs::subClassOf += [superclass] }
      sc::sameas.each     { |samenode|   node.owl::sameAs += [samenode] }

      node
    end

    # Add referenceable data if requested
    if options[:referenceable] and node.size > 0
      source                = reference(doc)
      source.sc::type       = sc::type
      source.sc::superclass = sc::superclass
      source.sc::sameas     = sc::sameas
      source.sc::relation   = sc::relation
      node.graph           << source
      node.sc::source       = source
    end
    
    # Variable object points to either a node or a literal
    # Return the object, as well as its subfragments (if any)
    # and the doc it was extracted from
    { :node=>object, :subfragments=>sc::subfragment, :doc=>doc }
  end.compact
end