your thoughts on a crazy idea please

I came across an old RDBM called Business System 12
(http://www.mcjones.org/System_R/bs12.html) a few days ago. It seemed
to have a much simpler method of specifying queries - more similar in
style to relation algebra than SQL. For example, some example code
might look like this.

view = join(rel_1, rel_2) --assertains join criteria
based on primary keys
filtered_view = select(condition_list, view)
result = project(attribute_list, filtered_view)

Ignoring for a minute that SQL is the accepted method of talking to
databases, and also acknowledging that SQL may be more expressive than
relational algebra, I wondered if it would be possible to extend
Postgresql to allow non-sql interfaces to simple database services.

I suppose it would be possible to convert statements like those above
into their SQL equivalent before passing them to an existing driver, but
from reading the docs, it seems that dbmses usually do these types of
operations once they have parsed the SQL anyway.

I'd be interested to hear your thoughts on the subject whatever they
are. Critical comments are particularly welcome (they might be quite
useful for getting this stupid idea out of my head ;-)).

Regards,
Andy