Agent programming in Dribble from beliefs to goals with plans Birna van Riemsdijk Wiebe van der Hoek...
-
date post
20-Dec-2015 -
Category
Documents
-
view
214 -
download
0
Transcript of Agent programming in Dribble from beliefs to goals with plans Birna van Riemsdijk Wiebe van der Hoek...
Agent programming in Dribble
from beliefs to goals with plans
Birna van RiemsdijkWiebe van der HoekJohn-Jules Ch. Meyer
Utrecht University John-Jules Meyer 2
Motivation
◊ Our group has done work on agent programming languages in the past– 3APL: beliefs and goals-to-do– GOAL: beliefs and goals-to-be
◊ Natural question: how to combine these?
Utrecht University John-Jules Meyer 3
Answer: Dribble
◊ Dribble is an agent programming language containing:– Beliefs– Goals-to-be– Goals-to-do (Plans)
Utrecht University John-Jules Meyer 4
Mental States
◊ Mental state – Belief base : set of prop. forms– Goal base : set of prop. forms– Plan : sequence of ‘basic
elements’ (imperative program)
Utrecht University John-Jules Meyer 5
Belief and Goal Formulas
◊ Belief formulas• B
◊ Goal formulas
• G• logical consequences of particular goal
are also goals, if not believed
◊ Logical combinations
Utrecht University John-Jules Meyer 6
Plans
◊ Plan is sequence of basic elements◊ Basic elements:
•Basic action •Abstract plan•If-then-else construct
Utrecht University John-Jules Meyer 7
Basic Actions
◊ Basic action•executable •belief update•goal update: goals removed when
realised (thru commitment strategy)
Utrecht University John-Jules Meyer 8
Abstract plans
◊ Abstract plan•not executable •abstraction mechanism (compare
procedures) •translation into basic actions
Utrecht University John-Jules Meyer 9
If-then-else
◊ If-then-else construct if then 1 else 2 fi
•executable •plan update
Utrecht University John-Jules Meyer 10
Executing Basic Actions
◊ A basic action has as effects:– Belief update
•E.g. after execution of moveLeft, the agent believes to have moved left
– Goal update•Indirect, side effect of belief update
via commitment strategy
Utrecht University John-Jules Meyer 11
Commitment Strategy
◊ Commitment strategy– connection between beliefs and goals
– when are goals dropped?• when believed to have been achieved
Utrecht University John-Jules Meyer 12
Goal Rules
◊ Goal rules have form – taken from GOAL : a– used for plan selection
– is condition on beliefs and/or goals• Beliefs: specify when the plan could be
executed• Goals: specify what the plan is good for
Utrecht University John-Jules Meyer 13
Goal Rules (ctd)
– applicable in E iff E (selection of new plan only if current plan is empty)
– resulting mental state is (adoption of plan )
Utrecht University John-Jules Meyer 14
PR Rules
◊ Practical Reasoning (PR) rules:h b
– taken from 3APL– is condition on beliefs– employed for
• Creating plans : p a;b;c
• Modifying plans : h b
• Modeling reactive behaviour : E b
Utrecht University John-Jules Meyer 15
PR Rules (ctd)
– applicable in h iff h
– resulting mental state is b (adoption of plan b instead of h )
Utrecht University John-Jules Meyer 16
Operational Semantics
◊ Operational semantics based on transition system
• definition of mental state transformations
◊ Transition rule for basic action execution
• T(a,) defines update of by executing action a
Utrecht University John-Jules Meyer 17
Transition rules
◊ Application of goal rule g:
E EapplyRule(g)
Utrecht University John-Jules Meyer 18
Transition Rules
◊ Execution of a basic action a:
T(a,) = ’_______________________aExecute(a) ’’E
where ’\’
Utrecht University John-Jules Meyer 19
Summary So Far
◊ Dribble agent– Mental state
• belief base, goal base, plan
– Goal rules• plan selection
– PR rules• plan creation and modification
Utrecht University John-Jules Meyer 20
Dynamic Logic
– specify and verify properties of programs
– programs: syntactic constructs in the logic
– p: possible to execute p and halt in state satisfying
– program is transformation function on states: reason about state transformations
Utrecht University John-Jules Meyer 21
Logic for Dribble
◊ Dynamic logic for Dribble– transformations on mental states
caused by:• goal and PR rule application and action
execution
– reason about state transformations• reason about rule application and action
execution of meta-actions
Utrecht University John-Jules Meyer 22
Syntax
◊ : sequence of meta-actions• applyRule(g), applyRule(), execute(a),
execute(if-then-else)
◊ : mental state formula• B(), G(), Com()
Utrecht University John-Jules Meyer 23
Semantics
◊ r* : semantics of meta-actions• transformation function on mental states through
meta-actions ◊ interpretation of diamond formulas:
– r*
◊ Com formulas– Com’’
Utrecht University John-Jules Meyer 24
Semantics
◊ Semantics of applyRule(g)
for g: ’
r* (applyRule(g)) (’
if = E and
Utrecht University John-Jules Meyer 25
Correspondence
◊ Mental state transitions
- defined by transition system(meaning of Dribble agent)
- defined by actions in the logic
(by means of the r* function)
Utrecht University John-Jules Meyer 26
Correspondence (ctd)
◊ Correspondence of logic and operational semantics– transition defined by actions in
the logic transition defined by transition system
– properties of actions in logic: properties of Dribble agent
Utrecht University John-Jules Meyer 27
Some Validities
◊ Results of meta-actions• [applyRule(g)] Com()
• Com(h) [applyRule()]Com(b)
• Com(a;) [a] [execute(a)](Com() )
• Com(if;) [execute(if)] Com(1), where if = if then 1 else 2 fi
[Where g: and : h b]
Utrecht University John-Jules Meyer 28
Some Validities (ctd)
◊ Realisability of meta-actions• Com(E) applyRule(g)T• Com(h) applyRule()
Com(b)
• Com(a;) aT execute(a)Com() • Com(if;) execute(if) T, where if = if then 1 else 2 fi
[Where g: and : h b]
Utrecht University John-Jules Meyer 29
Conclusion
◊ agent programming language– incorporating goals and planning
features– formally defined semantics
◊ programming logic– a first attempt to reason about these
‘self-modifying’ programs (via meta-actions)
Utrecht University John-Jules Meyer 30
Future Work
◊ incorporate first-order languages◊ selection of goal from wish base◊ explicit goal adopt and drop actions◊ drop goal when believed to be
unachievable◊ investigation of use of adding goal
formulas in PR rules