Lecture 7-2 CS250: Intro to AI/Lisp

Building Knowledge Bases

Lecture 7-2

February 18th, 1999

CS250

Lecture 7-2 CS250: Intro to AI/Lisp

Representational Adequacy

• Metaphysical adequacyCould the world have the representational form

suggested without a contradicting the facts of the aspect of the reality we’re interested in?

• Epistemological adequacyExpress facts about the world in a practical way

• Heuristic adequacyAre the reasoning processes used in solving a

problem expressible?

Lecture 7-2 CS250: Intro to AI/Lisp

General Ontologies

• Categories

• Measures

• Composite Objects

• Time, Space and Change

• Events and Processes

• Physical Objects

• Substances

• Mental Objects and Beliefs

Lecture 7-2 CS250: Intro to AI/Lisp

Composite Objects

• Not inheritance– Difference between subclass and member

• General event descriptions– Schema– Script

Lecture 7-2 CS250: Intro to AI/Lisp

Using Events to Represent Change

• What’s the problem?– Continuous time– Multiple agents– Actions of different durations

• Event calculus - Reify events

Lecture 7-2 CS250: Intro to AI/Lisp

Event Calculus Vocabulary

• Events are splotches in the space-time continuum

• Events have subevents

• Some events are intervals

Lecture 7-2 CS250: Intro to AI/Lisp

Examples

• Suppose we wish to represent facts about market manias

f fBulbEating SubEvent(f,TulipMania) PartOf(Location(f), Holland)

s sStockFrenzy SubEvent(s,USBullMarket) PartOf(Location(f), ??)

s sStockFrenzy SubEvent(s,USBullMarket) TradedOn(Exchange(s), NASDAQ)

Lecture 7-2 CS250: Intro to AI/Lisp

Place

• How are places like intervals?

• Relation In holds among places

• Location function: Maps an object to the smallest place that contains it

Lecture 7-2 CS250: Intro to AI/Lisp

Processes

• Why do we need processes when we have events?

• How can we say:– Barry Sonnenfeld was flying some time

yesterday

– Barry was flying all day yesterday

Kurt D. Fenstermacher:

Sonnenfeld directed:Men in Black (1997)Get Shorty (1995)The Addams Family (1991)

Kurt D. Fenstermacher:

Sonnenfeld directed:Men in Black (1997)Get Shorty (1995)The Addams Family (1991)

E(Flying(Barry), Yesterday)

T(Flying(Barry), Yesterday)

Lecture 7-2 CS250: Intro to AI/Lisp

A Logical Blender

Suppose Bill is accused of killing a zucchini, and when the cold, but efficient, Detective Frigerator (known to his pals as simply “Re”) questions the orange juice pitcher in FOPL, the orange juice has no idea how to say:

“Bill was in the kitchen with the tomato all day yesterday”

Lecture 7-2 CS250: Intro to AI/Lisp

Composite Events

• Use And to combine two events with the usual semantics:

And isn’t so bad, but disjunction is a bit more complicated -- how do we say:

“I saw the whole thing, the beef or the broccoli stabbed the zucchini all afternoon.”

p,q,e T(And(p, q), e) T(p, e) T(q, e)

Lecture 7-2 CS250: Intro to AI/Lisp

Time & Intervals

• Time is pretty important– Divvy up time into: Moments and ExtendedIntervals

– Define a couple handy functions

Start

End

Time

Date

Lecture 7-2 CS250: Intro to AI/Lisp

When Intervals Get Together

• Meet

• Before

• After

• During

• Overlap

Lecture 7-2 CS250: Intro to AI/Lisp

Objects in the Space-Time Continuum

• Remember that events are splotches of space-time

• Some events have coherence through time

• Need to capture the idea of an object existing through time

Lecture 7-2 CS250: Intro to AI/Lisp

Roman Empire

• Roman Empire spread across much of Eurasia, expanding and contracting, from 753 B.C. until the 5th century A.D.

Lecture 7-2 CS250: Intro to AI/Lisp

Roman Empire at 218 B.C.

Lecture 7-2 CS250: Intro to AI/Lisp

Roman Empire at 117 A.D.

Lecture 7-2 CS250: Intro to AI/Lisp

Roman Empire at 395 A.D.

Lecture 7-2 CS250: Intro to AI/Lisp

Fluents

• Roman Empire is an event– Subevents include

• First, Second and Third Punic Wars• One of the first known hammer and anvil

movements in battle (216 BC @ Cannae)

• A fluent allows us to capture the notion of the Roman Empire throughout time

T(Male(Emperor(RomanEmpire)), 1stCenturyAD)

T(In(Gaul, Roman Empire), AD12)

Lecture 7-2 CS250: Intro to AI/Lisp

Fluent Flavors

• Fluent is a function, f:Situations Fvalues– Domain is the set of all situations (states of

the world)

If Fvalues is {TRUE, FALSE} then it’s a Propositional fluent

If Fvalues is {All situations} then it’s a Situational fluent

Lecture 7-2 CS250: Intro to AI/Lisp

Substances

• Less vs. fewer

• Intrinsic vs. extrinsic properties

• Substances are those things that are fungible

Lecture 7-2 CS250: Intro to AI/Lisp

Going, Like, Totally Mental

• What are other agents know, and what are they thinking?– “Everybody’s looking at me”– “They’re trying to kill me”– “You look like someone who knows where I

can find extra virgin olive oil”

• Start with a Believes predicateBelieves(Agent, x)

Lecture 7-2 CS250: Intro to AI/Lisp

Reification & You

• A good first pass:

• Treat Flies(Superman) as a propositional fluent– Relationships like Believes, Know and When

between agents and propositions are propositional attitudes

• The problem: Can Clark fly?

Believes(Agent, Flies(Superman))

Lecture 7-2 CS250: Intro to AI/Lisp

“It is clear.”

• Referential transparency– Any term can be substituted for an equal

term– FOL is referentially transparent

Lecture 7-2 CS250: Intro to AI/Lisp

Knowing for Action

• Knowing preconditions: What do you need to know to do action a?

• Knowledge effects: What effect does performing action a have on an agent’s knowledge?

Lecture 7-2 CS250: Intro to AI/Lisp

Replacing that Zucchini

• Grocery shopping– Percepts– Actions– Goals– Environment