Integration PostgreSQL with Oracle.

Hi friends, greetings :-)
Please apologize by my bad english, I speak sapnish.

This question that I'll do could be a little difficult because I'm award
that it should be very especific, although I'm looking for a first guide or
directive in ordert to solve this dilemma.

I'm developing a Java-Web Software using PostgreSQL for a company in which I
work.

One of the requirements is, using whatever mechanism (external to my
Java-Web develop) to establish an interaction/integration/communication from
my PostgreSQL database toward an Oracle Database already existents and in a
production state inside the company,

I have heard about using XML in ordert to carry out Data Bases integrations
(from diferents manufacturers ) and even I have heard about using Web
Services (SOAP) but I don't sure.

Some of you has faced some similar situation? Could you suggest to me some
direction on that matter?

Beforehand thank you very much by your help and support.

Kind Regars.
Alfredo Rico.-