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Phases of Query Processing

Query processing is done in several phases, described below. We will illustrate what is done in each phase through a simple example: the question put to the user when the solution to the toplevel query X is 1+1 is displayed, requesting a decision whether to find alternative answers or not:

| ?- X is 1+1.

X = 2 ? no
Please enter ";" for more choices; otherwise, <return>
 ? ;

We focus on the query X = 2 ? in the above script.

The example query belongs to the class next_solution, its text is described by the message term solutions([binding("X",2)]), and its help text by the message term bindings_help. Accordingly, such a query is executed by calling:

ask_query(next_solution,               /* QueryClass */
          solutions([binding("X",2)]), /* Query */
          bindings_help,               /* Help */

In general, execution of ask_query(+QueryClass, +Query, +Help, -Answer) consists of the following phases: