local world = jecs.World.new()
local pair = jecs.pair
-- These components and functions are actually already builtin
-- but have been illustrated for demonstration purposes
local ChildOf = world:component()
local Name = world:component()
local function parent(entity)
    return world:target(entity, ChildOf)
end
local function getName(entity)
    return world:get(entity, Name)
end
local alice = world:entity()
world:set(alice, Name, "alice")
local bob = world:entity()
world:add(bob, pair(ChildOf, alice))
world:set(bob, Name, "bob")
local sara = world:entity()
world:add(sara, pair(ChildOf, alice))
world:set(sara, Name, "sara")
print(getName(parent(sara)))
for e, name in world:query(Name, pair(ChildOf, alice)) do
    print(name, "is the child of alice")
end
-- Output
-- "alice"
-- bob is the child of alice
-- sara is the child of alice