and Van Gelder and Topor [1987] may provide starting points for this
work.
It would be desirable to extend the results in this paper to languages that in-
clude functions. This will require new definitions of allowed and domain inde-
pendent formulas and a new proof that every allowed formula is domain inde-
pendent. The proof that every allowed stratified database is domain independ-
ent should then hold without change. Possible definitions are proposed in
Topor [1987].
The question of the relative merits of the two definitions of a correct answer
for a query with respect to a stratified database also deserves furthe ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month, and much more.