Oracle FAQ Your Portal to the Oracle Knowledge Grid
HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US
 

Home -> Community -> Usenet -> comp.databases.theory -> Re: relations aren't types?

Re: relations aren't types?

From: Vadim Tropashko <vadimtro_at_yho.cm>
Date: Tue, 30 Dec 2003 11:19:13 -0800
Message-ID: <SkkIb.9$7S6.170@news.oracle.com>


Mikito Harakiri wrote:

> Consider the "Group" type. Now, some groups are decomposable into direct
> products, like dihedral group D_3 (aka symmetric group S_3), while the
> others, like cyclic group Z_3, don't. I'm tempted to call Z_3 atomic, and
> S_3 composite value, then.

FYI there is a java library for groups. Dihedral group is there

http://jsci.sourceforge.net/api/JSci/maths/groups/DihedralGroup.html

but symmetric group apparently not. Alas, I was interested to doublecheck if D_3 = S_3:

Group d3 = DihedralGroup(3);
Group s3 = SymmetricGroup(3);
System.out.println(d3.equals(s3));

That looks just like a special case, but OOP claims that they eliminate special cases like this with subtyping, and I wonder how would they organize groups into hierarchy of types such that D_3 = S_3.

Returning back to Marshall's argument about programming language progress, note that int in java is atomic type, while java.lang.Integer

   is not. That's a solid foundation to advance relational implementation! Received on Tue Dec 30 2003 - 13:19:13 CST

Original text of this message

HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US