Properly clear triples in fuseki when updating a single play

[cmil]

Until now we only clear the fuseki graph for an entire corpus when we update the corpus in total. When updating individual documents of a corpus, ignorer to avoid duplicates, we would have to delete existing triples before posting a new RDF representation to the triple store the following way:

1. Remove triples of blank node used to hook wikidata-id to the creator of the play:

WITH <https://dracor.org/test> DELETE
	{
  		?play <http://dracor.org/ontology#has_author> ?node.
		?node ?p ?o .
	} 
WHERE 

{
  		?play <http://dracor.org/ontology#has_author> ?node.
		?node ?p ?o .
}	

2. remove Triples of characters of a single play:

WITH <https://dracor.org/test> DELETE {
    <https://dracor.org/entity/greek000026> schema:character ?character. 
    ?character ?p ?o
} WHERE {
    <https://dracor.org/entity/greek000026> schema:character ?character. 
    ?character ?p ?o
} 

3. remove Triples of the creation-event:

WITH <https://dracor.org/test> DELETE { 
    ?creation crm:P94_has_created <https://dracor.org/entity/greek000026> ;
    ?p ?o . } 
WHERE { 
    ?creation crm:P94_has_created <https://dracor.org/entity/greek000026> ;
    ?p ?o .
}

4. remove the remaining triples:

WITH <https://dracor.org/test> DELETE {
    <https://dracor.org/entity/greek000026> ?p ?o} 
WHERE {
    <https://dracor.org/entity/greek000026> ?p ?o
}

The problem is, that there is currently only a connection from the play to the character; so we have to remove them with a separate query. The information on the author of a play is attached at two points (1. cidoc-like via a creation event, 2. via property of the dracor-ontology dracon:has_author) We maybe could include it only once (1.?), this would save an update operation, but makes it probably more complicated to query the author-info. I should probably think of a way to include the inverse path of schema:character to connect play to character, but I'm not sure if this is possible within schema.org. And, maybe, the queries could be combined into one, but I unfortunately don't know how.

Prefixes I included while testing:

PREFIX frbroo: <http://iflastandards.info/ns/fr/frbr/frbroo/>
PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX schema: <http://schema.org/>
PREFIX crm: <http://www.cidoc-crm.org/cidoc-crm/>

Originally posted by @ingoboerner in #77 (comment)