Re: repeating groups

Marshall Spight wrote:
> I see no reason to add bags. In fact, I'm not even sure I
> believe a bag is an actual data structure. It seems more
> like a traversal strategy on a set. What makes you think
> you need bags?

Here is a snippet from old exchange "how is this collection called":

Let '*' be binary aggregation operator.

Then, sets obey the following laws:

a*a=a
a*b=b*a
a*(b*c)=(a*b)*c

Bags:

a*a!=a
a*b=b*a
a*(b*c)=(a*b)*c

Lists:

a*a!=a
a*b!=b*a
a*(b*c)=(a*b)*c

We see that progression to more complex collection types gives up more and more algebraic properties. Does this explain why colllection based algebras were not so successfull? Received on Sun Feb 19 2006 - 19:31:17 CET