We are using a simple database about oil pipelines. Each pipeline is owner by some

company. There are connection point where two pipelines can meet, even if owned by

different companies.

Pipeline$($id$,$ name, owner$)$

Company$($id$,$ name, stockprice$)$

Connection$($p$1$ id$,$ p$2$ id$)$

where p$1\_$id and p$2\_$id are each FKs to

Pipeline.id

We want to find the names of all pipelines which are directly connected to some pipeline

owned by a different company.

How can we express that in relational calculus?

$.$ name $|$ Pipeline Pipeline $(q{)}^{{?}^{?}}$ Connection $(p,q{)}^{{?}^{?}}p.$ ouner $$ q$.$owner