I assume with req/resp over http you meant RESTful web services. If you can make a choice, go for simple RESTful XML over http solution. Coz, you dont need any additional middleware infrastructure and in synchronous messaging your communicating systems are tightly coupled. More loosely coupled solution is a better SOA.
In case you meant otherwise, it is good to opt for a
SOAP based web service or a RESTful web service based on your specific needs.
Subramanian, Kumar [[email protected]]<br />J2EE Architect, <a href="http://www.eminenttech.com" target="_blank" rel="nofollow">Eminent Technology Solutions (ETS)</a><br />Software / Portals / Alfresco / Outsourcing / Proteomics