6.8 Queries

Introduction

Queries are just like the body of a rule:

• A query consists of one or more subgoals, separated by commas, and ended with a period:

  subgoal, subgoal, ..., subgoal.

• For the query to succeed, all of its subgoals must be satisfied by matching.
• This is done from right to left, in the order of the subgoals.

Queries are written in the Prolog+CG user interface, in the lower part of the main window.

Answers

A query always gives an answer. This can be:

1. no.

   meaning that the query did not succeed.

2. {}

   meaning "yes", or that the query did succeed and that there were no variable bindings.

3. A set of variable bindings, meaning that the query succeeded with the given variable bindings. For example:

   {X = gr1, Y = [Animal]}
   {X = gr2, Y = [Human]}