Middleware, there are hundreds of them and they function all alike. They exchange messages with SAP via RFC or XML over HTTP. There is no real need to look for SAP certification. He only thing to certify is, that the system can exchange messages with SAP and does not loose them. Nearly all of them make use of the RFC connectors for Windows (.NET connector, DCOM connector) or Java (JCo).
More important in all middleware scenarios is knowing how the middleware performs in your environment. If you already have one in your infrastructure, this will be the first choice. Some best selling middleware is: IBM WebSphere/MQ, Microsoft BIZTALK, SAP XI, Mercator, ZENOS, Seebeyond.
If you need advice, better check with your credit card clearing bank for alist of middleware they can communicate with.
This was first published in July 2004