[antlr-interest] Transformation to new grammar

[Barry McGillin]

I have a grammar for one version of SQL that I'm mapping into Oracle SQL.
We can walk the trees and generate what we need to however,  I have a full version of the target grammar available.  Is is possible to map from one grammar to another, so that it is possible to verify that tree n is correct wrt the target grammar as shown below.  

|Source Grammar |  tree 1 | ... | tree n | Target grammar|
|    o          |    o    |     |    o   |       o       |
|   / \         |   / \   |     |   / \  |      / \      |
|  o   o        |  o   o  |     |  o   o |     o   o     |
|     / \       | /     \ |     | / \    |    / \        |
|    o   o      |o       o|     |o   o   |   o   o       |

Today, we can walk the source tree and make transformations to it to move us from tree 1 towards tree n, but when do we know we're finished and correct? I'm not looking for a specific solution, but rather some ideas about how this can be done efficiently if at all :-)
Thanks guys
Barry