If the query was successful, the service will return a HTTP code 200.
In addition, if the RESPONSEFORMAT was set to VOTable, the VOTable result document will contain, in the RESOURCE element and before the TABLE element, the following snippet: <INFO name="QUERY_STATUS" value="OK" />.
Example:
<?xml version="1.0" encoding="UTF-8"?> <VOTABLE ... > .... <RESOURCE type="results"> <INFO name="QUERY_STATUS" value="OK" /> <TABLE> ... </TABLE> </RESOURCE> </VOTABLE>