About Linked Stage Graph

Goals

Creating the Knowledge Graph

What is a Knowledge Graph?

A knowledge graph is a "graph of data with the intend to compose knowledge".

Graph of data refers to a data set viewed as a set of entities represented as nodes, with their relations represented as edges.
Composing knowledge refers to a continual process of extracting and representing knowledge that enhances the interpretability of the resulting knowledge graph.

A knowledge graph is therefore a method to create and organize knowledge in a continuing process in a way that it can be interpreted by humans and machines alike.

Source: "Knowledge Graphs: New Directions for Knowledge Representation on the Semantic Web". Bonatti et al.

Workflow

From XML (EAD-DDB) to RDF

The metadata was provided using the XML EAD standard which is used for encoding descriptive information regarding archival records. In order to create a knowledge graph, the data has to be transformed into the Resource Description Framework (RDF).
Many XML to RDF converters already exist, but due to the unique structure of the provided metadata, none of them worked out of the box. In the end, we used the XML2RDF converter by rhizomik and we used and adapted an EADRDF XSLT Stylesheet. Both outputs were imported into OpenLink Virtuoso. We connected both outputs using owl:sameAs and the archival unit ids. This enabled us to merge both outputs by semantic reasoning.

Named Entity Extraction and Linking (Connecting with Others)

The provided metadata contains interesting information about the performances and photographs in form of semi-structured or unstructured text. For example, the resource http://slod.fiz-karlsruhe.de/labw-2-2599390 has a title (dcterms:title) and an abstract (dcterms:description). These semi-structured textual information as shown in the first table below can be interpreted by humans, but not by machines. Therefore they cannot be queried or visualized in a meaningful and useful way. We started to tackle this issue in two steps:

• We extract named entities from semi-structured text. In the example below, named entities are e.g. the title "Was ihr wollt" or names like "Felix Cziossek".
• If available, we mapped the extracted named entities to existing knowledge bases, Wikidata and the German National Library (GND)

Before Linking

dcterms:title	Was ihr wollt (William Shakespeare)
dcterms:description	Schauspiel Art und Datum der Aufführung: Neuinszenierung, 11.03.1923 Inszenierung: Curt Elwenspoek Bühnenbild: Felix Cziossek Kostüme: Ernst Pils

After Linking

dcterms:title	Was ihr wollt (William Shakespeare)
dcterms:description	Schauspiel Art und Datum der Aufführung: Neuinszenierung, 11.03.1923 Inszenierung: Curt Elwenspoek Bühnenbild: Felix Cziossek Kostüme: Ernst Pils
schema:isBasedOn	<http://www.wikidata.org/entity/Q221211> <http://d-nb.info/gnd/4316770-6>
dbo:setDesigner	<http://www.wikidata.org/wiki/Q55638867>
schema:contributor	<http://www.wikidata.org/entity/Q692>

In the second table above, several mappings were created. For instance, Felix Cziossek was mapped to the respective Item in Wikidata using the property dbo:setDesigner and the play "Was ihr wollt" was mapped to the respective creative work in Wikidata and GND using the property schema:isBasedOn.

What does this mean?

In this example, we have now created new knowledge in the form of human and machine interpretable facts:

• the fact that the resource http://slod.fiz-karlsruhe.de/labw-2-2599390 with the title "Was ihr wollt" is based on the famous play Twelfth Night by William Shakespeare, and
• the fact that Felix Cziossek was the set designer for that play at the Stuttgart Theater.

These new and structured information can now be queried using SPARQL. Another advantage of linking these entities from our knowledge graph to other knowledge graphs is that we can make use of all data linked to these resources (e.g. in Twelfth Night) as you can see in the Lodview Linked Open Data widget.

Exploration

We have created several means of exploration. For non-technical users who simply want to enjoy the photographs along with their descriptions and relevant persons, we have created the Linked Stage Graph Viewer and we have utilized the Vikus Viewer. For technically advanced users, we provide an endpoint to be queried using SPARQL.

SPARQL Endpoint

You can query the Linked Stage Graph using our SPARQL-Endpoint.

Use the following prefixes with your query:

	PREFIX dcterms: <http://purl.org/dc/terms/>
	PREFIX gnd: <http://d-nb.info/gnd/>
	PREFIX schema: <http://schema.org/>
	PREFIX slod: <http://slod.fiz-karlsruhe.de/>
	PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
			

Example Query 1: Query Linked Stage Graph

Select all resources and their labels, for which there is a contributor (schema:contributor) listed in the data set. Optionally, also show the genre of each resource (schema:genre).
(Query Demo)

    SELECT DISTINCT ?resource ?label ?contributor ?name ?genre
    WHERE {
        ?resource schema:contributor ?contributor .
        ?resource rdfs:label ?label .
        ?contributor rdfs:label ?name .
        OPTIONAL {?resource schema:genre ?genre }
        }

Example Query 2: Federated Query (via Wikidata)

Select all resources, each resource label and their respective representation in Wikidata (schema:isBasedOn). Additionally, query Wikidata for these resources and select the publication year for each resource.
(Query Demo)

    SELECT distinct ?resource ?resourcelabel ?publicationdate
	WHERE {
		?resource schema:isBasedOn ?wikiresource .
		?resource rdfs:label ?resourcelabel .
	
		SERVICE <https://query.wikidata.org/sparql> {
			?wikiresource <http://www.wikidata.org/prop/direct/P577> ?publicationdate .
				}
		}

Disclaimer: When the Wikidata server is busy, this federated query may cause a timeout. If this occurs, please try again a few minutes later. Thank you!

Example Query 3: Federated Query (via DBpedia)

Select the English language abstracts of each linked resource (e.g. persons and plays).
(Query Demo)

		
	SELECT DISTINCT ?resource ?resourcelabel ?dbp ?abstract
	WHERE {
		?resource schema:isBasedOn ?wikiresource .
		?resource rdfs:label ?resourcelabel .

		SERVICE <http://dbpedia.org/sparql> {
			?dbp ?p ?wikiresource .
			FILTER regex(?dbp, 'http://dbpedia.org/', 'i')
			?dbp <http://dbpedia.org/ontology/abstract> ?abstract .
			FILTER (lang(?abstract) = 'en') .
		}	

Disclaimer: When the DBpedia server is busy, this federated query may cause a timeout. If this occurs, please try again a few minutes later. Thank you!

Team