You can create an ontology from an existing database schema. The pattern of a database is interpreted as a simple ontology. Tables are taken as classes, columns as properties and columns with "foreign keys" as relations. In addition, a set of rules is provided to connect the real facts in the database to the ontology.
This means that only the structure of the database is imported, but the real data resides in the database. During runtime of a query, only the required facts are retrieved from the database in order to answer the query.
NOTE: Multiple imports from the same database within the same project can lead to serious performance problems and are not allowed!
NOTE: It is not allowed to choose other columns as instance key if the table has a primary key!