实现通用Web服务API的最佳方式

What is the best way to implement a open/cross platform web service API to an existing .NET App? Not being a strictly .NET friendly API. It already has ASP.NET exposed web services, but need to be built into an generic API allowing inserts, updates and deletes and returning results based on user criteria in standard SOAP, JSON or other common formats, similar to Google's Data API's.What is the best way to implement a open/cross