ASTL constraints are all in the form of backward-chaining constraints.
The user can only issue queries. However, an intelligent agent has the ability to not only acquire information about situations and obtain new information about them by being attuned to assorted constraints, but also act accordingly to alter its environment. Thus, having forward-chaining constraints as well would be better. In this way, new situations would be created, new infons would be inserted into situations, and consequences of new infons would be observed. This can be achieved by introducing a situation which is global to all other situations and then asserting the constraint in this global situation.