# Wikidata Support in the Creation of Rich Semantic Metadata for Historical Archives
## 3 Mapping from the Wikidata Semantic Model to HERO
### Knowledge Base Access
All those Wikipedia or BabelNet entities for which no link to a Wikidata entry exists are lost in the mapping. For example, given the list of Wikipedia entities [_Interrogation_, _Interrogation_(_TV_series)]_, we have \(M\)([_Interrogation_, _Interrogation_(_TV_series)]) = [Q327018, Q60753100]; i.e., the corresponding list of Wikidata entities. If we apply the mapping function \(M\) to the query results listed above, we obtain the following entity lists in the Wikidata space:  
* \(M\)_(Q(Wikipedia, interrogation)) = [Q327018, Q60753100];
* \(M\)_(Q(Wikipedia, interrogatorio)) = [Q327018, Q56323357];
* \(M\)_(Q(Wikidata, interrogation)) = [Q327018, Q60753100, Q6056617, Q6056611];
* \(M\)_(Q(Wikidata, interrogatorio)) = [Q327018, Q56323357, Q3800554];
* \(M\)_(Q(BabelNet, interrogation)) = [Q327018, Q189756]_ (in this case, the mapping function returns only two correspondences, since the _bn:00047209n BabelNet_ synset does not have any Wikidata correspondence);
* \(M\)_(Q(BabelNet, interrogatorio)) = [Q327018, Q56323357, Q195414]._  
Therefore, the outputs of the Knowledge Base Access step are six ordered lists of elements in the Wikidata space, for each \(<l^{C}\)\({}_{em}\), \(l^{C}\)\({}_{\mu}\)> \(\in\)\(L^{C}\). In our example, we obtain the six lists for the pair of labels _!interrogation_, _interrogatorio_?, as well as the six lists for _!questioning_, _interrogatorio_? (see Figure 5). **(3) Scoring. ** The Scoring step is composed of the Candidates Selection and Voting subsets. If none of them occurs in the results of that query, we randomly choose one of them. The whole process does not always return a correspondence for the HERO category \(C\). In fact, the following may happen:  
* The Candidates Selection substep returns \(Candidates^{C}=\emptyset\). This may happen when the Knowledge Base Access step returns only empty lists for each pair of labels \(<\)\(l^{C}_{\mathit{cm}}\), \(l^{C}_{\mathit{i}}\)\(>\)\(\in\)\(l^{C}\);
* The Voting substep finds a best matching Wikidata category \(M(C)\) with a confidence score lower than the threshold \(\theta\). **Evaluation of the approach. **  
We exploited the same approach for both classes and individuals in HERO. The ontology contains 429 classes; 189 of them have a corresponding entity in the Wikidata space, while for 240, no correspondence exists. Additionally, the ontology contains 145 individuals: For the vast majority of them, a correspondence does exist, and for only 32 of them, it does not. Then, we manually fixed the matching strategy errors by either choosing the appropriate Wikidata category for HERO categories with a possible match or by setting \"no correspondence\" for HERO categories with no Wikidata correspondence. We evaluated our automatic matching strategy in order to estimate its reliability and reusability: Since both Wikidata and HERO are constantly evolving, the same approach will be adopted with new versions of the two models; therefore, we are interested in assessing its suitability in the perspective of its reuse. We considered the following as correct results: (i) the returned associations between a HERO category and its actual Wikidata corresponding category; (ii) the returned \"no correspondence\" answer for those HERO categories for which no Wikidata corresponding category exists. We considered the following as wrong results: (i) the returned associations between a HERO category and a wrong Wikidata category, for those HERO categories for which a correspondence exists; (ii) the returned \"no correspondence\" answer for the HERO categories for which a Wikidata corresponding category does exist; (iii) the returned associations between a HERO category and a Wikidata category, for those HERO categories for which no correspondence exists. We consider the reference matching set RM of the actual correspondences between HERO and Wikidata categories and the set SM of the correspondences returned by the system.