Creating a new set from components of an existing set in OPL/CPLEX - optimization

Question

I have a set that I have read into my OPL project that looks like this:
S = {<"A","">, <"B","">, <"AB","A">, <"AB","B">, <"C","">, <"ABC","A">,<"ABC","B">, <"ABC","C">, <"ABC","AB">},
where each element <,> is a tuple with two string elements. This set represents parent-child relationships between items of interest.
From this set I need to create a new set:
S' = {<"A",{""}>, <"B",{""}>, <"C",{""}>, <"AB",{"A","B"}>, <"ABC",{"A","B","C","AB"}>},
where each element <,> is a tuple with the first element of each tuple a string and the second element of each tuple a set of strings. My attempt at creating this set is:
tuple child{
string Item;
string Child;
}
{child} Children = ...; //Reads in the set S
tuple dependents{
string Item;
{string} ItemChildren;
}
{dependents} dependentsSet = {<x.Item, y.Child> | x in Children, (y in Children : <x,y> in Children)};
Using the variable names from the above code, the purpose of creating S' is because later in my program I need to create a collection of constraints, one for each Item, and within each constraint I need to index over the ItemChildren. I'm a relative novice with OPL so I know I'm using the syntax incorrectly in the initialization of the dependentsSet variable, but I don't know how to write this statement correctly such that it creates the set I'm looking for.
Can anyone help me understand the statements required to create the set I'm after?

Answer 1

tuple child{
string Item;
string Child;
}
{child} Children
= {<"A","">, <"B","">, <"AB","A">, <"AB","B">, <"C","">, <"ABC","A">,
<"ABC","B">, <"ABC","C">, <"ABC","AB">};
{string} setOfParents={i.Item | i in Children};
{string} setOfChildren={i.Child | i in Children};
tuple dependents{
string Item;
{string} ItemChildren;
}
{string} kids[p in setOfParents]={k | k in setOfChildren : <p,k> in Children};
{dependents} dependentsSet = {<x, kids[x]> | x in setOfParents};
execute
{
writeln(dependentsSet);
}
gives
{<"A" {""}> <"B" {""}> <"AB" {"A" "B"}> <"C" {""}>
<"ABC" {"A" "B" "C" "AB"}>}