Legalo

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Revision as of 22:56, 13 June 2014

Legalo

Subgraphs identification algorithm (implemented by the Semantic Web property extractor)

   algorithm legalo is
       input G: a RDF graph  from FRED
       output S: a set of RDF triples expressing semantic relations between named entities recognized in G
   
       let E the set of named entities in G
       let C the set of all named entity pairs combinations including permutations
   
       for each named entity e1 in E
           for each named entity e2 in E
               if e1 != e2'
                   add <e1, e2'> to C
   
       let P a set of tuples <e1, e2, sub-graph>
       let DFS stand for depth first search
   
       for each pair <e1, e2> in C
           directPaths ← DFS in G retrieving all direct paths between e1 and e2
           if directPaths is not empty
               for each directPath in directPaths
                   add <e1, e2, directPath> to P
           else  
               for each node of type dul:Event event in G
                   leftSubGraph ← DFS in G for retrieving the shortest direct paths connecting e1 and event
                   rightSubGraph ← DFS in G for finding the shortest direct paths connecting event and e2
                   if rightSubGraph does not contain agentive roles
                       add <e1, e2, rightSubGraph> to P
       
       let S a set of RDF triples
       
       for each tuple <e1, e2, sub-graph> in P
           property ← produce semantic web relation based on sub-graph
           add RDF triple e1 - property - e2 to S

Producing semantic web relations

Legalo produces a semantic web relation property based on each sub-graph included in P (cf. legalo algorithm) The label of property is generated by concatenating the labels included in the sub-graph according to a number of heuristics derived by incremental empirical observations. These heuristics are continuously evolving. Currently, the main ones are summarizes as follows:

• Given a direct path between e₁ and e₂, the label of property will be produced by concatenating the arc labels in the path and the more general types' labels of the nodes in the path. See example below:

   dbpedia:Felix :memberOf dbpedia:All_Star_Band
   dbpedia:All_Star_Band :of dbpedia:Rino_Starr
   dbpedia:All_Star_Band rdf:type :Band

   would generate

   label(property) = memberOfBandOf

   and

   dbpedia:Felix :memberOfBandOf dbpedia:Ringo_Starr

• a label of a semantic relation is generated by concatenating the properties found in the statements from an event to an object
• some mappings between properties and terms of a semantic relation are performed according to the following criteria
  • vnrole:Beneficiary → for
  • vnrole:Instrument → with
  • vnrole:Destination → to
  • vnrole:Topic → about
• while traversing the statements, also the types of subject nodes are taken into account. Namely, given a subject node its most general FRED type is added into the label of a semantic relation
• repetitions of terms into a label of a semantic relation are avoided, i.e. in case of consecutive properties in a sub-graph such as born born only one is used into a semantic relation