Well, I suppose so.
Strictly speaking, Sharepoint is not a relational database. Mind, it has many uses and it may be powered by SQL Server, but the lists themselves are not relational. Now, at least they did make it so that Sharepoint 2010 supports referential integrity & cascade deletes, presumably by doing some magic behind the scene so from a end user's POV, it's still the same thing as how we've defined ways in Access.
Relationships on Sharepoint are defined by Lookup fields only, BTW.