I'm stuck up inside a problem in which I have to query a sharepoint server to come back all of the sites(top sites) present in the same level. For instance, Basically query sharepoint server to come back all of the top sites that are in the same level as those of "http://vmsp2010-1", it will return all top sites. I've got a web server implemented in Java that is located around the Apache Tomcat server. Out of this web server, I have to query sharepoint server to come back all of the top sites that are in the same level in sharepoint. Please tell me The Way I could query the sharepoint server.

I do not think SharePoint's OOB Web Services supports what you're searching for. Possibly, you would like to produce a custom web service of yours and obtain their email list of site collections. You'll have to write the code using SharePoint Object Model and host this logic in the custom web service.