1. Agent Communications BDI Definitions
CPSC /CPSC
Rob Kremer
Department of Computer Science
University of Calgary
Based on: Michael Wooldridge. Reasoning about Rational Agents. MIT Press, Cambridge, Mass Chapter 2.
09/11/2018

2. CPSC 609.68/599.68: Agent Communications
Plan
Plan
Preconditions: P Predicate
Postconditions: P Predicate
Actions: Seq Action
hd: Plan  Action // returns head(Plan.Action)
tail: Plan  Plan // returns {Pre,Post,tail(Actions)}
09/11/2018
CPSC /599.68: Agent Communications

3. CPSC 609.68/599.68: Agent Communications
BDI Agent
BDIagent
B: P Bel
D: P Des
I: P Int
getNextPercept:   Percept
brf: P Bel  Percept  P Bel
options: P Bel  P Int  P Des
filter: P Bel  P Des  P Int  P Int
plan: P Bel  P Int  Plan
execute: Plan
09/11/2018
CPSC /599.68: Agent Communications

4. CPSC 609.68/599.68: Agent Communications
A simple BDI agent
B := B0; I := I0; /* B0 are initial beliefs; I0 are initial intentions */
while true do {
p := getNextPercept();
B := brf(B,p);
D := options(B,I);
I := filter(B,D,I);
 := plan(B,I);
execute() }
Stuck to a plan: If the plan fails (becomes unsound) then the agent really should change the plan.
09/11/2018
CPSC /599.68: Agent Communications

5. BDI Agent that reacts if plan is unsound
B := B0; I := I0; /* B0 are initial beliefs; I0 are initial intentions */
while true do {
p := getNextPercept();
B := brf(B,p);
D := options(B,I);
I := filter(B,D,I);
 := plan(B,I);
while not empty() do {
a := hd();
execute(a);
 := tail();
if not sound(,I,B) then }
Deals with unsound plans, but won’t drop intentions: What if we have unexpected early success or conditions arise that make our intentions useless or unobtainable? We might want to change our intentions.
09/11/2018
CPSC /599.68: Agent Communications

6. BDI Agent that may drop intentions
B := B0; I := I0; /* B0 are initial beliefs; I0 are initial intentions */
while true do {
p := getNextPercept();
B := brf(B,p);
D := options(B,I);
I := filter(B,D,I);
 := plan(B,I);
while not (empty() or suceeded(I,B) or impossible(I,B)) do {
a := hd();
execute(a);
 := tail();
if not sound(,I,B) then }
But if the environment changes, we may need to reconsider intensions.
09/11/2018
CPSC /599.68: Agent Communications

7. Cautious Agent that reconsiders after each action
B := B0; I := I0; /* B0 are initial beliefs; I0 are initial intentions */
while true do {
p := getNextIntention();
B := brf(B,p);
D := options(B,I);
I := filter(B,D,I);
 := plan(B,I);
while not (empty() or suceeded(I,B) or impossible(I,B)) do {
a := hd();
execute(a);
 := tail();
p := getNextPercept();
if not sound(,I,B) then }
But this agent might spend almost all of it’s time considering intensions and no time actually doing useful stuff.
09/11/2018
CPSC /599.68: Agent Communications

8. BDI Agent that attempts to strike a balance
B := B0; I := I0; /* B0 are initial beliefs; I0 are initial intentions */
while true do {
p := getNextPercept();
B := brf(B,p);
D := options(B,I);
I := filter(B,D,I);
 := plan(B,I);
while not (empty() or suceeded(I,B) or impossible(I,B)) do {
a := hd();
execute(a);
 := tail();
if reconsider(I,B) then {
I := filter(B,D,I); }
if not sound(,I,B) then }
This is only useful if reconsider() is a lot cheaper than options() and filter().
09/11/2018
CPSC /599.68: Agent Communications