integrate website with offline system

I have a website that provides a booking system. A lot of my costumers already have an offline booking system that also gives them other funcionalities(POS, Accounting, etc.). So they usually ask me to integrate my online booking system with their offline booking system. 开发者_开发知识库

This means: when someone books in the offline system, it should replicate to the website. And when someone books in the website, it should replicate to the offline system.

I've been thinking about WebServices, but I think it's the wrong approach. I'd have to implement WebService Server in all my clients so I can save the appointments that are made on the web to their offline system. I'm also reading about middlewares, B2B, EAI, but I can't see a clear picture about the solution.

Any help would be appreciated

If you haven't found a solution for this I would recommend using WCF, they are more secure, more flexible and faster. Also does it have to be a real-time update? Could you have a nightly process that uploads/downloads the daily activity and refresh for the next day. One last thing is security, be sure your using SSL to pass the data.