[sc34wg3] Look Ma! No Properties!

[Robert Barta]

On Fri, Jul 16, 2004 at 12:22:52PM +0200, Jan Algermissen wrote:
> Question on 2.1:
> I assume that the assertions in the tuples (a1,a2,...an) all have the
> same set of roles, yes? If not, how would the projection operator work?

The projection simply picks a particular assertion out of a tuple. It
is basically what the SELECT clause in SQL does:

   SELECT name
   FROM table

> I am missing how you determine that two assertions have the same set
> of roles?

The individual assertions in < a_1, a_2, ...., a_n > can be completely
different, and they will be usually. So there is no need that they
have 'the same form', i.e. share the exact same set of roles.

\rho