Infopath query aganist the sharepoint sitecollection using webservice.

there is a infopath field with sitecollectionURL.and i have to check  this field with a webmethod that returns a boolean(sitecollection exists or not with that name in farm). i am attaching code snippets..but it is not working...can anyone help me out..and correct my code snippet..why it is not working?Start Free Trial

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public static bool Exists(Uri uri)
{
bool returnvalue;
returnvalue = SPSite.Exists(uri);
return returnvalue;
}