Monotonic tables depend on monotonic dynamic predicates. In some
situations there is external dynamic data such as a database. One
solution is to maintain a shadow copy of all the external data in a
dynamic predicate. This wastes resources and introduces maintenance
problems. The system allows to use this information directly from the
external source. To do this, create a dynamic and monotonic predicate
that accesses the data:
:- dynamic my_data/2 as monotonic.
my_data(X, Y) :-
<access external data>.
Any monotonic table that depends on my_data/2 will be populated
correctly and build a dependency. Next, if a new answer is added to the
external data the user must call incr_propagate_calls/1
from the Prolog library library(increval). Similarly, when
an answer is removed from the extenal data we use incr_invalidate_calls/1.
Both notification calls must be made after the external data
has been updated, i.e., my_data/2 must reflect the new situation before
calling incr_propagate_calls/1
or incr_invalidate_calls/1.
:- use_module(library(increval)).
on_new_my_data(X, Y) :-
incr_propagate_calls(my_data(X, Y)).
on_removed_my_data(X,Y) :-
incr_invalidate_calls(my_data(X, Y)).
- incr_propagate_calls(:Answer)
- Activate the monotonic answer propagation similarly to when a new fact
is asserted for a monotonic dynamic predicate. The Answer
term must match a monotonic dynamic predicate. See
section 7.8.3
for an example.
Status
Monotonic tabling is experimental and incomplete. Notably support for
answer subsumption and call subsumption is probably
possible and may greatly improve the application domain and resource
usage. Monotonic tabling should work with both shared and private
tables. Concurrency issues have not yet been tested though.
