In these approaches, it is considered that an ontology and a legacy
database already exist. The goal is to create mapping between
them, and/or populate the ontology by the database contents.
Mappings here are more complex than those in the previous case
because different levels of overlap between the database domain
and the ontology’s one can be found, and those domains do not
always coincide because the modeling criteria used for designing
databases are different from those used for designing ontology
models