Sovereign information sharing allows autonomous entities to compute queries across their databases in such a way that nothing apart from the result is revealed. We describe an implementation of this model using web services infrastructure. Each site participating in sovereign sharing offers a data service that allows database operations to be applied on the tables they own. Of particular interest is the provision for binary operations such as relational joins. Applications are developed by combining these data services. We present performance measurements that show the promise of a new breed of practical applications based on the paradigm of sovereign information integration.