SPARQL using union with a dataset

Question

The challenge set is to use the UNION keyword with the following datasets and return a list of grandads.

RELDB1 holds 2 useful tables:

The fatherOf table has this data:

Table fatherof:
('Chuck', 'Paul'),
('Chuck', 'Bonnie'),
('Jerry', 'George'),
('Jerry', 'Mary'),
('Chuck', 'Olivia'),
('Paul', 'Joan'),
('George', 'John'),
('George', 'Carole'),
('Ringo', 'Yoko'),
('Ringo', 'Peter')

and the table Person has:

Table person:
('Sara', 64, 'f'),
('Nancy', 68, 'f'),
('Mary', 27, 'f'),
('Olivia', 37, 'f'),
('Bonnie', 35, 'f'),
('Carole', 7, 'f'),
('Yoko', 6, 'f'),
('Joan', 9, 'f'),
('Chuck', 67, 'm'),
('Jerry', 65, 'm'),
('Paul', 30, 'm'),
('George', 25, 'm'),
('Ringo', 39, 'm'),
('John', 8, 'm'),
('Peter', 11, 'm')

I tried this query:

>SELECT ?x ?y ?z  
>WHERE {{?x rdf:type ex:Person}  
>UNION  
>{?x ex:fatherOf ?y . ?y ex:fatherOf ?z}}  
>ORDER BY (?x)

The output was everyone in the Person table and then also the son and grandchild for Chuck (Paul, Joan) and Jerry (George, John and George and Carole). I tried removing ?y ?z. The query returned a list of the person table!

How can I modify the query so that the UNION remains but I get only grandparents. Any guidance would be appreciated.

Answer 1

You are trying to return every person who is a grandfather. In your question you show that you are only returning paternal grandparents ...

A grandfather has children who has children who has children.

                                        Grandfather
                              Son                    Daughter
                        Son       Daughter       Son        Daughter

The union part come into play because you are going to return the following:

1. ?z father of ?a
2. ?a mother of ?b

3. ?a father of ?b

    ?z ?a ?a ?b ?b ?b ?b

You need a union on the mother and father of ?b as you are combining the results of multiple triple patterns. I won't provide you with the query for this as this is classwork, however, this should help you arrive at the answer using what you have.