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CS344 : Introduction to Artificial Intelligence
Pushpak BhattacharyyaCSE Dept., IIT Bombay
Lecture 10a- knowledge representation
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Predicate Calculus Introduction through an example (Zohar Manna,
1974): Problem: A, B and C belong to the Himalayan
club. Every member in the club is either a mountain climber or a skier or both. A likes whatever B dislikes and dislikes whatever B likes. A likes rain and snow. No mountain climber likes rain. Every skier likes snow. Is there a member who is a mountain climber and not a skier?
Given knowledge has: Facts Rules
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Predicate Calculus: Example contd. Let mc denote mountain climber and sk denotes skier.
Knowledge representation in the given problem is as follows:
1. member(A)2. member(B)3. member(C)4. ∀x[member(x) → (mc(x) ∨ sk(x))]5. ∀x[mc(x) → ~like(x,rain)]6. ∀x[sk(x) → like(x, snow)]7. ∀x[like(B, x) → ~like(A, x)]8. ∀x[~like(B, x) → like(A, x)]9. like(A, rain)10. like(A, snow)11. Question: ∃x[member(x) ∧ mc(x) ∧ ~sk(x)]
We have to infer the 11th expression from the given 10. Done through Resolution Refutation.
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Knowledge representation
Requirements: Adequacy (I) (also called completeness) Correctness (II) Efficiency (III)
I/II/III
Representational Inferential Acquisitional (learning)
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Representation KnowledgeShould be able to represent everything in scope (expressive power)
Correct
Efficient
Semi-structured (Eg: Xml database)
Unstructured (Eg: Plain text)
Structured (Eg: tables)
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• Examine tables as a knowledge representation scheme
• How do tables fair in terms of
-Adequacy
-Inference
-Acquisition ?
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Student name
Height Weight BMI
Ram 5.6 76 xyz
Shyam 6.2 63 pqr
John 5.1 56 abc
• Consider the question “Which student is the tallest?”
• Without a procedure to calculate max, the question cannot be answered. (Needs Inferencing)
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Other knowledge representation schemes
1. Propositional calculus
2. Predicate calculus
3. Semantic net
4. Frames
Predicate calculus is considered as the epitome of KR in terms of adequacy and inferencing
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Inferencing in PC
Resolution Forward chaining
Backward chaining
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Knowledge
Declarative Procedural
• Declarative knowledge deals with factoid questions (what is the capital of India? Who won the Wimbledon in 2005? Etc.)
• Procedural knowledge deals with “How”
• Procedural knowledge can be embedded in declarative knowledge
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Example: Employee knowledge base
Employee record
Emp id : 1124
Age : 27
Salary : 10L / annum
Tax : Procedure to calculate tax from basic salary, Loans, medical factors, and # of children
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Text Knowledge Representation
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A Semantic Graph
in: modifiera: indefinite
the: definite
student
past tense
agent
bought
objecttime
computer
new
June
modifier
The student bought a new computer in June.
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UNL representation
Ram is reading the newspaper
Representation of Knowledge
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Knowledge Representation
Ram
read
newspaper
agt obj
UNL Graph - relations
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Knowledge Representation
Ram(iof>person)
read(icl>interpret)
newspaper(icl>print_media)
UNL Graph - UWs
agt obj
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Knowledge Representation
Ram(iof>person)
read(icl>interpret)
newspaper(icl>print_media)
@entry@present@progress
@def
Ram is reading the newspaper
UNL graph - attributes
agt obj
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The boy who works here went to school
plt
agt@ entry @ past
school(icl>institution)
go(icl>move)
boy(icl>person)
work(icl>do)
here
@ entry
agt plc
:01
Another Example
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UNL System
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Universal Networking Language
Universal Words (UWs) Relations Attributes Knowledge Base
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UNL Graph
obj
agt
@ entry @ past
minister(icl>person)
forward(icl>send)
mail(icl>collection)
He(icl>person)
@def
@def
gol
He forwarded the mail to the minister.
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UNL Expression
agt (forward(icl>send).@ entry @ past, he(icl>person))
obj (forward(icl>send).@ entry @ past, minister(icl>person))
gol (forward(icl>send ).@ entry @ past, mail(icl>collection). @def)
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Universal Word (UW)
What is a Universal Word (UW)? What are the features of a UW? How to create UWs?
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What is a Universal Word (UW)? Words of UNL Constitute the UNL vocabulary, the syntactic-
semantic units to form UNL expressions A UW represents a concept
Basic UW (an English word/compound word/phrase with no restrictions or Constraint List)
Restricted UW (with a Constraint List ) Examples:
“crane(icl>device)” “crane(icl>bird)”
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The Features of a UW
Every concept existing in any language must correspond to a UW
The constraint list should be as small as necessary to disambiguate the headword
Every UW should be defined in the UNL Knowledge-Base
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Restricted UWs
Examples He will hold office until the spring of next year. The spring was broken.
Restricted UWs, which are Headwords with a constraint list, for example:
“spring(icl>season)” “spring(icl>device)”“spring(icl>jump)”“spring(icl>fountain)”
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How to create UWs? Pick up a concept
the concept of “crane" as "a device for lifting heavy loads”
or as “a long-legged bird that wade in water in search of food”
Choose an English word for the concept. In the case for “crane", since it is a word of
English, the corresponding word should be ‘crane'
Choose a constraint list for the word. [ ] ‘crane(icl>device)' [ ] ‘crane(icl>bird)'
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UNL Relations Constitute the syntax of UNL Expresse how concepts(UWs) constitute a
sentence Represented as strings of 3 characters or
less A set of 41 relations specified in UNL (e.g.,
agt, aoj, ben, gol, obj, plc, src, tim,…) Refer to a semantic role between two lexical
items in a sentence E.g., John has composed this poem.
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AGT / AOJ / OBJ AGT (Agent)
Definition: Agt defines a thing which initiates an action
AOJ (Thing with attribute)Definition: Aoj defines a thing which is in a state or has an attribute
OBJ (Affected thing)Definition: Obj defines a thing in focus which is directly affected by an event or state
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Examples John broke the window.
agt ( break.@entry.@past, John)
This flower is beautiful.aoj ( beautiful.@entry, flower)
He blamed John for the accident.obj ( blame.@entry.@past, John)
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BEN BEN (Beneficiary)
Definition: Ben defines a not directly related beneficiary or victim of an event or state
Can I do anything for you?ben ( do.@entry.@interrogation.@politeness, you )obj ( do.@entry.@interrogation.@politeness, anything
)agt (do.@entry.@interrogation.@politeness, I )
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BEN : UNL Graph
obj
agt
@ entry @ past
baby(icl>child)
carve(icl>cut)
toy(icl>plaything)
he(iof>person) @def
ben
He carved a toy for the baby.
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GOL / SRC
GOL (Goal : final state)Definition: Gol defines the final state of an object or the thing finally associated with an object of an event
SRC (Source : initial state)Definition: Src defines the initial state of object or the thing initially associated with object of an event
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GOL I deposited my money in my bank account.
objagt
@ entry @ past
account(icl>statement)
deposit(icl>put)
money(icl>currency)
I
gol
bank(icl>possession)
mod
mod
mod
I I
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SRC They make a small income from fishing.
objagt
@ entry @ present
fishing(icl>business)
make(icl>do)
income(icl>gain)
they(icl>persons)
src
small(aoj>thing)
mod
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PUR PUR (Purpose or objective)
Definition: Pur defines the purpose or objectives of the agent of an event or the purpose of a thing exist
This budget is for food.pur ( food.@entry, budget )mod ( budget, this )
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RSN
RSN (Reason)Definition: Rsn defines a reason why an event or a state happens
They selected him for his honesty.agt(select(icl>choose).@entry, they)obj(select(icl>choose) .@entry, he)rsn (select(icl>choose).@entry, honesty)
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TIM
TIM (Time)Definition: Tim defines the time an event occurs or a state is true
I wake up at noon.agt ( wake up.@entry, I )tim ( wake up.@entry, noon(icl>time))
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TMF
TMF (Initial time)Definition: Tmf defines a time an event starts
The meeting started from morning.obj ( start.@entry.@past, meeting.@def )tmf ( start.@entry.@past, morning(icl>time) )
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TMT
TMT (Final time)Definition: Tmt defines a time an event ends
The meeting continued till evening.obj ( continue.@entry.@past, meeting.@def )tmt ( continue.@entry.@past,evening(icl>time) )
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PLC PLC (Place)
Definition: Plc defines the place an event occurs or a state is true or a thing exists
He is very famous in India.aoj ( famous.@entry, he )man ( famous.@entry, very)plc ( famous.@entry, India)
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PLF
PLF (Initial place)Definition: Plf defines the place an event begins or a state becomes true
Participants come from the whole world.
agt ( come.@entry, participant.@pl )plf ( come.@entry, world )mod ( world, whole)
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PLT
PLT (Final place)Definition: Plt defines the place an event ends or a state becomes false
We will go to Delhi.agt ( go.@entry.@future, we )plt ( go.@entry.@future, Delhi)
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INS
INS (Instrument) Definition: Ins defines the instrument to carry out an event
I solved it with computeragt ( solve.@entry.@past, I )ins ( solve.@entry.@past, computer )obj ( solve.@entry.@past, it )
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INS : UNL Graph
objagt
@ entry @ past
blanket(icl>object)
cover(icl>do)
baby(icl>child)
John(iof>person)
@def
ins
John covered the baby with a blanket.
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Attributes Constitute syntax of UNL Play the role of bridging the conceptual world
and the real world in the UNL expressions Show how and when the speaker views what is
said and with what intention, feeling, and so on Seven types:
Time with respect to the speaker Aspects Speaker’s view of reference Speaker’s emphasis, focus, topic, etc. Convention Speaker’s attitudes Speaker’s feelings and viewpoints
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Tense: @past
The past tense is normally expressed by @past
{unl}agt(go.@entry.@past, he)…{/unl}
He went there yesterday
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Aspects: @progress
{unl}man
( rain.@entry.@present.@progress, hard )
{/unl}
It’s raining hard.
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Speaker’s view of reference
@def (Specific concept (already referred))The house on the corner is for sale.
@indef (Non-specific class)There is a book on the desk
@not is always attached to the UW which is negated.
He didn’t come. agt ( come.@entry.@past.@not, he )
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Speaker’s emphasis
@emphasisJohn his name is.
mod ( name, he )aoj ( John.@emphasis.@entry, name )
@entry denotes the entry point or main UW of an UNL expression
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UNL Knowledge Base (UNLKB)
What is the UNL Knowledge Base? Linguistic Background How to define the UWs in the UNL
Knowledge-Base?
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What is the UNL Knowledge Base?
A semantic network comprising every directed binary relation between UWs
Categorized according to the role of a concept to other concepts