SQL access to graph based solutions means that queries are created in SQL and then converted into SPARQL or other graph query language. For the most part, this means that there’s a need to create in advance a set of SPARQL queries or components which relate to SQL query statements, so constant maintenance and availability of SPARQL skilled personnel is required. In addition, the data is stored in a graph database so there’s a constant need to ETL data from the source to graph format.
In the case of a SQL knowledge graph, semantic SQL queries use the standard SQL commands and are not transalated into a separate graph query language. The data itself remains on site without need to be transformed.