A short Prolog script that works with a family dataset. There are basic commands to reason the relationships of the members of the family.

Parents.pl

/*
 * Project Name:        	Parents
 * Solution Name:		Parents
 * Original creation date:	01/10/2006
 * Edit date:			11/10/2013
 * Programmer name:		Jamie Taylor (aka "GaProgMan")
 * File name:			parents.pl
 * 
 * Purpose of the project:
 *	This project was undertaken as coursework in class
 *	08226 (Artificial Intelligence). The purpose of this
 *	coursework was to make students aware of how relationships
 *	are created between data objects in a Prolog code listing.
 *		We were given a list of people and their
 *	relationships with each other and were told to create
 *	a reasoning engine that could answer basic questions
 *	about the relatioships between the people.
 *		The user could then ask the Prolog engine
 *	questions based on the initial data set, and the Prolog
 *	engine would then be able to provide the correct answer
 *		The questions where "Who is the child of X?",
 *	"Who is the grandparent of X?", "Who is the sibling of X?",
 *	and "Who is the inlaw of X?"	
 *
 *	GNU Copyright information
 *	Copyright 2011 Jamie Taylor <jamie@taylorj.org.uk>
 *
 *	This program is free software; you can redistribute
 *	it and/or modify it under the terms of the GNU General
 *	Public License as published by the Free Software
 *	Foundation; either version 2 of the License, or (at
 *	your option) any later version.
 *
 *	This program is distributed in the hope that it will
 *	be useful, but WITHOUT ANY WARRANTY; without even the
 *	implied warranty of MERCHANTABILITY or FITNESS FOR A
 *	PARTICULAR PURPOSE.  See the GNU General Public
 *	License for more details.
 *
 *	You should have received a copy of the GNU General
 *	Public License along with this program; if not, write
 *	to the Free Software Foundation, Inc., 51 Franklin
 *	Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/

parent(frank,george). 		%the parent of frank is george
parent(helen,frank).   		%the parent of helen is frank
parent(amy,frank).    		%the parent of amy is frank
parent(mick,frank).		%the parent of mickis frank
parent(emma,helen).		%the parent of emma is helen
parent(susan,helen).		%the parent of susan is helen
parent(john,amy).		%the parent of john is amy
parent(paul,amy).		%the parent of paul is amy
parent(ringo,amy).		%the parent of ringo is amy
parent(steven,mick).		%the parent of steven is mick
parent(charlie,mick).		%the parent of charlie is mick
parent(bob,mick).		%the parent of bob is mick
parent(beth,mick).		%the parent of beth is mick
parent(kylie,emma).		%the parent of kylie is emma

partner(george,mildred).	%george's partner is mildred
partner(frank,betty).		%frank's partner is betty
partner(helen,geoffrey).	%helen's partner is geoffrey
partner(amy,richard).		%amy's partner is richard
partner(mick,sue). 		%mick's partner is sue
partner(emma, jason). 		%emma's partner is jason

/* The child of method takes two arguments: X and Y, and
 * seeks to reason whether Y is the child of X. It will
 * then return whether Y is the child of X
 */
child_of(Y, X):-		% Y is a child of X if
	parent(Y, X).		% X is a parent of Y

/* The grand parent methos takes two arguments: X and Z,
 * and seeks to reason whether Z is the grandchild of X.
 * It does so by recursively calling the parent method
 * to see whether X is the parent of Y, and whether Y is
 * the parent of Z. If so, then Z is the grandchild of X
 */
grandparent_of(X,Z):-		% X is a grandparent of Z if
	parent(X,Y),		% X is the parent of Y and 
	parent(Y,Z).		% Y is the parent of Z

/* The sibling method takes two arguments: X and Y, and
 * seeks to reason whether they are siblings.
 * The simplest way of doing this is to check whether
 * they share any parents.
 */
sibling_of(X,Y):-		% X is a sibling of Y if
	parent(X,Z),		% Z is X's parent and 
	parent(Y,Z).		% z is also Y's parent

/* The inlaw method takes two arguments: A and X, and seeks
 * to reason whether they are inlaws by checking  who the
 * partner of A is and whether on of said partner's parents
 * are X.
 */
inlaw(A, X):-			% X is an inlaw of A if
	partner(B, A),		% A had a partner B and
	parent(B, X),		% B had a parent X.
	write(X),
	write(' is an inlaw of '),
	write(A).

/* The inlaw method takes two arguments: A and X, and seeks
 * to reason whether they are inlaws by checking  who the
 * partner of A is and whether on of said partner's siblings
 * are X.
 */
inlaw(A, X):-			% X is an inlaw of A if
	partner(B, A),		% A had a partner B and
	sibling_of(B, X),	% B had a sibling X.
	write(X),
	write(' is an inlaw of '),
	write(A).