OCL Primer (3)

use> ? let u=Tuple{n:'john',a:22} in (u.a>=18) and not (u.n='')
use> \ 
> ? let 
> u1=Tuple{n:'john',a:22},
> u2=Tuple{n:'kate',a:20},
> u=Set{u1,u2}
> in u->collect(a)
> .
> ... How to get the mean age ?

Thus, OCL knows objects (represented by tuples) and classes (i.e. sets of objects).

Now, its more easy to use the GUI (and load pre-defined models as explained later):

let ps=Set{Tuple{n:'john',a:22},Tuple{n:'kate',a:20}},
as=ps->collect(a)
in as->sum()/as->size()