P.S.

> But can someone of your team describe the rationale behind usage of arrays
> as representation of matrices/vectors,

(It was Jerome who decided that, but anyway...)  The reason was
convenience: we could write matrix/vector multiplication by using
for-loops, for instance.  As for the efficiency,
"records > tuples = arrays (without boundary checks)" and as for the
safety, "records = tuples > arrays", I suppose.