A recap on a scientific paper (a rant) on the use of logic in artificial intelligence

1. “Rigor Mortis” - in brief
The response to Nilsson’s
“Logic and artificial intelligence”
Øyvin Halfdan Thuv
Department of Computer and Information Science
11. October 2006
www.ntnu.no Øyvin Halfdan Thuv, “Rigor mortis” - in brief

2. 2
Logical methods must be adequate
— If you state an axiom, keep the intended usage in mind!
The QA3-system exemplifies this:
— QA3 is “logical methods applied”
— It does not perform well on “heavy” problems ...
— ... unless problem is formulated properly
www.ntnu.no Øyvin Halfdan Thuv, “Rigor mortis” - in brief

3. 3
Logical methods must be adequate
QA3 critiques conclude:
— Must categorize with regard to abstraction sometimes
— Not just with regard to the world
— E.g.: Automatic programming: Language knowledge or
problem knowledge important?
Birnbaum conclude:
— If categorising is just a “shorthand” for real world knowledge
then categorising is futile → The conclusions that can be
drawn from the world are still the same.
— Focus on high level conceptualisations
www.ntnu.no Øyvin Halfdan Thuv, “Rigor mortis” - in brief

4. 4
Recursive knowledge formulation
— Process models depend on knowledge
— Knowledge must be formulated with regard to the model
— .. round and round we go
Birnbaum:
This is excatly why logicists continue to pretend that knowledge
can be formulated independently of use. What we should do is
to create the model while we formulate the knowledge.
Approximate continously!
www.ntnu.no Øyvin Halfdan Thuv, “Rigor mortis” - in brief

5. 5
Whats the use of logic then?
— We can pretend that knowledge and knowledge use is
somewhat independent
— What does that buy? → We can study smaller parts with logic
— Birnbaum claims that this has led to success before1
— Just don’t be too formal ...
— and keep it always in context
1
He does not prove, nor reference to any such success stories, though.
www.ntnu.no Øyvin Halfdan Thuv, “Rigor mortis” - in brief

6. 6
Other problems with logic
The frame problem:
— How to describe what is not affected by an action
— Problems with expressiveness
— Birnbaum claims that keeping lists of what to change (and
what not to change) isn’t really logicism, it’s just a way of
controlling the assertions of the actual logic engine.
www.ntnu.no Øyvin Halfdan Thuv, “Rigor mortis” - in brief

7. 7
Other problems with logic
Reasoning with models:
— Efficiency
— Nilsson: Sometimes just a small part of the “intended model”
is needed
— Birnbaum: Why ever consider using more than needed then?
www.ntnu.no Øyvin Halfdan Thuv, “Rigor mortis” - in brief

8. 8
Other problems with logic
The practicallity of deduction
— Nilsson: Large scale AI systems depend on First-Order
Predicate Calculus (FOPC)
— Birnbaum: At least one of the systems mentioned is not large
scale
— ... and it is slow too.
— Conclusion: FOPC isn’t practical for large-scale AI-systems2
2
Quite a conclusion to draw from this...
www.ntnu.no Øyvin Halfdan Thuv, “Rigor mortis” - in brief

9. 9
Logics are annoying to read
because more detail is involved, it usually takes more
work to uncover bugs in axiomatic theories than in
theories stated in english3
— It isn’t worth the effort of reading logic papers.
— Birnbaum: Forbus is right, except the part about the detail level
3
Forbus 1987
www.ntnu.no Øyvin Halfdan Thuv, “Rigor mortis” - in brief

10. 10
Logics are annoying to read
— “Fred the turkey” is probably dead
— Humans prefer known causes
— Logicians would maybe see this if they wrote english instead
of FOPC
“Fred is dead because we prefer to think in banes that makes all
events have known causes”
“Fred is not dead because we prefer the soultion that postpones
our knowledge of the situation as long as possible (even though
that satisfies the fluent-logical way of solving a “frame problem”
puzzle”
www.ntnu.no Øyvin Halfdan Thuv, “Rigor mortis” - in brief

11. 11
Summarising
— Logical methods is interdependent of their usage
— Knowledge is tied to process modeling, and vice versa
— Logics have problems with “framing”, expressiveness and
efficiency
— They are annoying to read → bewilderness
www.ntnu.no Øyvin Halfdan Thuv, “Rigor mortis” - in brief

12. FOPC First-Order Predicate Calculus
QA3 Question-Answer system 3
www.ntnu.no Øyvin Halfdan Thuv, “Rigor mortis” - in brief