Re: header part of the value?

Jan Hidders <hidders_at_gmail.com> wrote in news:2c892007-19bb-45ce-b73c- 6cdc6c8de229_at_o77g2000hsf.googlegroups.com:

> On 24 feb, 19:48, Marshall <marshall.spi..._at_gmail.com> wrote:

>> Consider the algorithm to perform a natural join on two
>> relation values. Just values: not tables in a database
>> with a known schema or whatever. Just two plain relation
>> values. The natural join specification *requires* the header;
>> it is defined (in part) in terms of the header. So the header
>> must be part of the value.

> 
> That is not correct. The natural join can be defined without referring
> to the header.
> 

Quite right. The header can always be extracted from a tuple by a simple function application:

tuple = {(x, 1), (y, 2)}; first_el(tuple) => {x, y} Received on Thu Feb 28 2008 - 18:08:12 CET