If you set the type of an attribute to "Transformable" then you can simply assign
an NSSet
to it:
e.setOfStrings = [NSSet setWithObjects:@"a", @"b", @"c", nil];
Core Data will use the NSCoding
methods to transform the set into a data blob and
store that in the SQLite store.
A disadvantage might be that you cannot search for strings in the set in a fetch request. If you need that feature then you have to use a to-many relationship instead.