1. 1 CS 2710, ISSP 2160 Chapter 12 Knowledge Representation

2. 2 KR Last 3 chapters: syntax, semantics, and proof theory of propositional and first-order logic Chapter 12: what content to put into an agent’s KB How to represent knowledge of the world

3. 3 Natural Kinds Some categories have strict definitions (triangles, squares, etc) Natural kinds don’t Define a cup (distinguishing it from bowls, mugs, glasses, etc) Bachelor: is the Pope a bachelor? But logical treatment can be useful (can extend with typicality, uncertainty, fuzziness)

4. 4 Upper Ontologies An ontology is similar to a dictionary but with greater detail and structure Ontology: concepts, relations, axioms that formalize a field of interest Upper ontology: only concepts that are meta, generic, abstract; cover a broad range of domain areas IEEE Standard Upper Ontology Working Group

5. 5 Anything AbstractObjects GeneralizedEvents Sets Numbers RepresentationalObjects Interval Places PhysicalObjects Processes Categories Sentences Measurements Moments things stuff times weights animals agents solid liquid gas Lower concepts are specializations of their parents

6. 6 Categories and Objects I want to marry a Swedish woman –Category of Swedish woman? –A particular woman who is Swedish? Choices for representing categories: predicates or reified objects basketball(b) vs member(b,basketballs) Let’s go with the reified version…

7. 7 Facts about categories and objects in FOL An object is a member of a category A category is a subclass of another category All members of a category have some properties (necessary properties) Members of a category can be recognized by some properties (sufficient properties) A category as a whole has some properties

8. Before continuing: inspiration for creative reification! From Through the Looking Glass 8

9. 9 Relations between categories Two or more categories are disjoint if they have no members in common: –Disjoint(s)  (  c 1,c 2 c 1  s  c 2  s  c 1  c 2  Intersection(c 1,c 2 ) ={}) Example: Disjoint({animals, vegetables}) A set of s categories constitutes an exhaustive decomposition of a category c if all members of the set c are covered by categories in s: –ExDecomp(s,c)  (  i i  c   c 2 c 2  s  i  c 2 ) Example: ExDecomp ({Americans, Canadians,Mexicans},NorthAmericans).

10. 10 Relations between categories A partition is a disjoint exhaustive decomposition: Partition(s,c)  Disjoint(s)  E.D.(s,c) Example: Partition({Males,Females},Persons) Is ({Americans,Canadians, Mexicans},NorthAmericans) a partition? Categories can be defined by providing necessary and sufficient conditions for membership  x Bachelor(x)  Male(x)  Adult(x)  Unmarried(x)

11. 11 Composite Objects partof(england,europe) All X,Y,Z ((partof(X,Y) ^ partof(Y,Z))  partof(X,Z)) Heavy(bunchOf({apple1,apple2,apple3}))

12. 12 Physical composition Often characterized by structural relations among parts. E.g. Biped(a) 

13. WrapUp We covered Chapter 12 through 12.2.1 13