Relational Algebra Rename Operation

Question

I have this relational algebra query:

%x(code)({('PX5'),('PX6')})

Can you explain to me what this query means?

I know that % is rename operation, x is new name of table, but I dont know, what is in () brackets behind '(code)'. Thank you

Answer 1

{('PX5'),('PX6')} looks like a relation. But I also don't understand your term. A rename is defined as ρ_a/b(R).

So the best what I could think of your term would be something like ρ_x/code({('PX5'),('PX6')}), which means:

Rename the attribute 'code' into 'x' of the relation {('PX5'),('PX6')}.