Re: What is Aggregation? Re: grouping in tuple relational calculus

Mikito Harakiri wrote:
>
> All of them -- sets, bags, and lists -- have their place in RM. The
> importance is shifted heavily toward the left side: bags are only important
> in the context of aggregation, and lists are even less important as the
> "order by" SQL clause is virtually the only usage for them.

Indeed. Frankly, I fail to see any big difference between our positions.

> Once again, if we loose accociativity, then we have to expand our semantics
> spectrum to admit trees

Not necessarily. Structural recursion over lists is often based on this.

• Jan Hidders