Anytime Hypothetical Reasoning
Aditya Kumar Ghose
University of Wollongong
This report describes the Anytime THEORIST system which supports
the following kinds of queries in the context of hypothetical reasoning:
- Explanation.
- Coherence.
- Set-membership.
- Set-entailment.
For each of these queries, the user is offered a choice of the
following anytime query processing strategies:
- Predicate restriction: The user will need to explicitly provide a
set of predicate symbols of interest and impose a stratification on this
set (i.e. partition the set into priority classes). When interrupted
during the course of processing a query, the system shall return a
partial solution (a partial scenario/extension for explanation and
coherence queries and a boolean value for set-membership and
set-entailment queries) together with the subset of the set of predicate
symbols that were considered in the available time.
- Formula restriction: The user will need to explicitly provide a
set of formulae of interest and impose a stratification on this set.
When interrupted, the system shall return a partial solution together
with the subset of the set of formulae of interest that were considered
in the available time.
- Theory restriction: The user will need to impose a stratification
on the set of hypotheses H. When interrupted, the system shall return
a partial solution together with an indication of the subset of H that
it was able to consider in the time available.
- Abstraction-based strategies: The user will need to specify the
subsets of the set of hypotheses H that can be abstracted away in the
initial stages of query processing. When interrupted, the system shall
return a partial solution together with a specification of the
abstractions of the specified subsets of H that were considered in
arriving at this solution.
The system is implemented in a modular fashion, with distinct
modules for each functionally distinct task. Thus, there are
modules for each of the four classes of supported queries and
sub-modules for each anytime query processing strategy. Special care
has been taken to ensure that the consistency checking module has a clean
separation from and a well-defined interface with the rest of the
system. This will permit the system to be applied in other domains with
distinct representation languages and notions of consistency (such as
over-constrained systems).
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