If Enterprise Level Federated Query is a hoax then what?

Couple days ago I received an email with the comment to my previous blog entry Enterprise Federated Query is a hoax!. The comment stated that Enterprise Federate Query is not impossible. It is not impossible but rather improbable. According to my previous blog entry, what I meant by an enterprise federated query is a user querying "n" data sources and the responses from the "n" data sources are combined and a unique set of results is passed to UI which then renders it for the end user. This is not possible since they are performance issues, governance issues, security issues and other functional and technical barriers. I believe with current technology and with smart human resources. It is possible to create a functional federated query with twenty to thirty data sources. Twenty or thirty data sources is no where close to 500 or 10,000 data sources.

The question to be asked then "what can be achieved with a SOA enterprise?". I believe rather than a request/response model, a publish/subscribe model is more robust and extensible. If data sources can publish new data or updated data to a topic then the topic clients can subscribe to the data sources' data. This way clients can subscribe to the data they want. Service Level Agreements (SLA) should be written and agreed upon on how the data can be manipulated or stored. Metadata repositories and registries are essential for any SOA enterprise to be successful with the publish/subscribe model.