Help needed for replacing triples in Op object

Hello,

I was searching for a way to replace the triples into the original sql
query.
I found the following in your group...

The algebra part of ARQ also supports the visitor pattern but also a
transform pattern for rewriting one algebra expression into another
(transform actually builds on visitor).  Subclass TransformCopy and
add your manipulation of BGPs; use class Tranformer to apply your
transform.  It's a bottom-up rewrite of the algebra form.  This is the
better way to manipulate queries - ARQ uses itself for some
optimizations, and uses the visitor pattern for reference evaluation
and serialization into SSE as in your example.

I used op visitor to visit the Op object and i got into bgp object and
accessed triples. Now i have the original object and the new triples.
How to build the whole Op object ( same as original ) but with
replaced triples. YOu have written that we should do bottom-up
rewrite, but can you help me how to proceed with it ?

Thanks a lot in advance.

Regards,

Arpita Agrawal