Handling queries which return no results

Sometimes users will submit a query which no objects in the catalogue satisfy. For example, the query might correspond to an empty patch of sky. In practice such queries are quite common. Unfortunately, the ACL format does not prescribe the action the server should take in this case. However, the recommended action is for the server to return an empty TST table. That is, it should return all the header information for a TST generated from the catalogue being queried (see Section ), down to and including the list of column names and the line of dashes anf tab characters which terminate the header, but no table of values.