Details are kindly requested regarding the mapping ontology in the GraphQL Virtuoso engine

Following the guidelines Usage Guide – Virtuoso GraphQL Views Creation & Management it is possible to implement a simple GraphQL bridge to the graphs.

More complex scenarios require more complex definitions of mapping schemas using Mapping Ontology About: RDF Ontology to GraphQL mappings schema. In particular, when there is no one-to-one mapping of graph entities to GraphQL entities, such ontology elements like Function and sparqlQuery can be used.

However comments in ontology give only a shallow description for these elements.
Can be an example provided to explain better the use cases for application of these elements ?