As you know in Caché / IRIS you have the possibility to define a property as Multidimensional as documented here:
and the explanation of how to use it
Though the access is quite comfortable (in traditional COS sense) there are 2 main restrictions that hurt:
#1) It is not saved to disk unless your application includes code to save it specifically.
#2) It cannot be stored in or exposed through SQL tables
there are some more
I'll show how to overcome these limits