If you were to log in, you'd be able to get more information on your fellow community member.
It is unfortunate this page helps perpetuate myths and misinformation about databases.
It says there are RDBMSes in the market today. There is only one, Alphora Dataphor. All the others are SQL DBMSes, and SQL violates too many fundamentals of the relational model to be called a relational language. Therefore, SQL DBMSes aren't RDBMSes.
As a consequence, it says RDBMSes are slow. SQL DBMSes are slow, but RDBMSes needn't be, as the relational model defines that the physical model can be quite different than the logical model of the database. Thus, one can keep a clean logical model yet implement all kinds of optimisations in the physical level. That is what SQL optimisers try to do, but due to SQL complexity and confusion of the logical and physical model they fail.