TO post a single triple attribute to a SubjectURI through the API, what is the endpoint to do so through?
The triples can potentially be stored in a separate context as Data Fusion will integrate the information using subjectURI or a custom context for the authenticating user is created if no contextId is provided.
At a minimum, the RDF requires an rdf:type and the label predicates defined as the system will reject the RDF otherwise. No explicit stitching is required if the subjectURI matches the subjectURI in another context that you would like to annotate. It is important that the entity type mappings are the same across contexts.
Did you check the REST API documentation (see here - http://docs.datafusion.thomsonreuters.com/restapi)?
Most information regarding API queries, including your instance's endpoint, can be found there along with sample queries.
This requires a file.
For the other, an error returns. As this is not a new entity.
"error": "Unable to create the entity with the newEntityUri, preferredLabelPredicate, and rdf parameters supplied. Please check the parameters and try again." }
POST/ entity Sending, curl -X POST --header 'Content-Type: text/plain' --header 'Accept: application/json' --header 'Authorization: Bearer vvj8o71dfgtda46ic7d4tnvnrllr010i' -d '<http://rdf.entagen.com/ns/document/be0e516244f18db78f54997a6e6b60e5> <http://ont.tr.com/ppty/hasSentiment> "0.5" .' 'https://dds-test.thomsonreuters.com/datafusion/api/entity?entityTypeId=3&newEntityUri=http%3A%2F%2Frdf.entagen.com%2Fns%2Fdocument%2Fbe0e516244f18db78f54997a6e6b60e5&preferredLabelPredicate=http%3A%2F%2Fwww.w3.org%2F2000%2F01%2Frdf-schema%23label'