13. A querying system comprising: memory which stores instructions for executing a query for retrieving results from an associated knowledge resource, the instructions including: a query engine which executes a query containing a global backreference and retrieves results from the knowledge resource responsive to the query, the query including a set of conditions, a first of the conditions including a regular expression that identifies strings in the knowledge resource that match the regular expression, the regular expression including a capturing group for capturing a substring of an identified matching string, the global backreference retrieving the substring captured by the capturing group and wherein the global backreference comprises a remote backreference which is outside the first condition and outputs at least one of the results of the query containing the global backreference and information based on the results; and a processor which executes the instructions.
13. A querying system comprising: memory which stores instructions for executing a query for retrieving results from an associated knowledge resource, the instructions including: a query engine which executes a query containing a global backreference and retrieves results from the knowledge resource responsive to the query, the query including a set of conditions, a first of the conditions including a regular expression that identifies strings in the knowledge resource that match the regular expression, the regular expression including a capturing group for capturing a substring of an identified matching string, the global backreference retrieving the substring captured by the capturing group and wherein the global backreference comprises a remote backreference which is outside the first condition and outputs at least one of the results of the query containing the global backreference and information based on the results; and a processor which executes the instructions. 15. The system of claim 13 , wherein each global backreference in the query is configured for retrieving a captured substring captured by a capturing group of the regular expression to which the global backreference refers when the regular expression matches a string in the knowledge source that includes the substring.