friends-of-friends.gql

############################################# SCHEMA #############################################
define
person sub entity,
    has name,
    plays friend;

friendship sub relation,
    relates friend;

name sub attribute, datatype string;

############################################# DATA #############################################
insert
$brandon isa person, has name "Brandon";
$travis isa person, has name "Travis";
$bob isa person, has name "Bob";
$mark isa person, has name "Mark";
$melissa isa person, has name "Melissa";
$louise isa person, has name "Louise";
$alice isa person, has name "Alice";

(friend: $brandon, friend: $travis) isa friendship;
(friend: $brandon, friend: $bob) isa friendship;
(friend: $brandon, friend: $mark) isa friendship;
(friend: $brandon, friend: $melissa) isa friendship;
(friend: $bob, friend: $mark) isa friendship;
(friend: $mark, friend: $louise) isa friendship;
(friend: $melissa, friend: $louise) isa friendship;
(friend: $melissa, friend: $alice) isa friendship;

############################################# QUERY #############################################
#Write a query to find the friends of Brandon’s friends
match
$brandon isa person, has name "Brandon";
$brandon_friends isa person;
($brandon, $brandons_friends) isa friendship;

$friends_of_brandons_friends isa person;
($brandons_friends, $friends_of_brandons_friends) isa friendship;
$friends_of_brandons_friends != $brandon;
not {
	($brandon, $friends_of_brandons_friends) isa friendship;
};
get $friends_of_brandons_friends;

#Create a rule to infer two people may be acquaintances based on mutual friends
define
person plays possible_acquaintance;
possible-acquaintanceship sub relation,
    relates possible_acquaintance;

people-who-may-know-each-other sub rule,
when {
    $a isa person;
    $b isa person;
    $c isa person;
    $r1 (friend: $a, friend: $b) isa friendship;
    $r2 (friend: $b, friend: $c) isa friendship;
    $a != $c;
    not {
        (friend: $a, friend: $c) isa friendship;
    };
}, then{
    (possible_acquaintance: $a, possible_acquaintance: $c) isa possible-acquaintanceship;
};

#E.g. Who is friends with Brandon's friends?
match $brandon isa person, has name "Brandon";
$r ($brandon, $x) isa possible-acquaintanceship;
get;

#E.g. Who has the most friends in common with Brandon?
match
$brandon isa person, has name "Brandon";
($brandon, $brandons_friends) isa friendship;
($brandon, $possible_acquaintances) isa possible-acquaintanceship;
$r ($possible_acquaintances, $brandons_friends) isa friendship;
get $r, $possible_acquaintances; group $possible_acquaintances; count;