>
>Although non-relational tools are allowed, it must be
> possible to manage the database using only relational tools, and the
> non->relational tools must not be allowed to bypass the integrity
> constraints imposed by the relational tools.
>
> For example, primary key uniqueness is maintained by an index in VFP.
> There are ways to open tables from outside VFP, without the index, and
> create duplicate primary keys. Referential integrity can be broken by
> similar means.
>

_this_ sounds more like a question of whether or not your candidate for a
RDBMS is implemented with a (database engine) server. in VFP you can
make DDL & DML changes directly to table structures and values,
respectively. in Oracle, for example you do not. you issue requests
(for DDL & DML) to the server which implements those requests on your
behalf and therefore can totally enforce RI and any other constraints.
(is it an anomally that you can temporarily disable constraints in Oracle?) for what it's worth, indexes are stored in separate tables in Oracle too,
and i dont' think anybody questions whether it's a true RDBMS.

i wonder if said professor isn't thinking more in terms of whether
or not the candidate DMBS has features like a transaction manager, and
other such abstraction layers.