Cyc: Common Sense Reasoning

1
Cyc Common Sense Reasoning

• An attempt to construct a common sense
  knowledge-base
• Effort of about 10 years of coding, a
  person-century according to the earlier article
  (more than that to this point)
• 1,000,000 common sense facts and rules
• General-purpose knowledge-base to be used with
  other applications

2
CycL

• A language used to encode Cycs KB
• Originally, it was a frame-like system (I.e.
  loosely organized objects)
• Rules represented in free-form ways depending on
  their specific intentions
• Uncertainty would be signified using certainty
  factors
• Found to be too awkward and updated around 1990

3
Updated CycL

• Updated version did without certainty factors and
  instead used relative rankings
• P is more likely than Q
• First order predicate calculus used for facts and
  rules
• Categories of facts and rules arranged
  hierarchically but using a directed graph instead
  of a tree

4
CycLs usefulness

• There is a range of representations from
• expressive (e.g., frames, semantic nets) to
• efficient (e.g., CDs with built-in inferencing
  mechanisms)
• CycL attempts to compromise by using
• a general-purpose representation
• category-specific inferences and assumptions
• It sacrifices completeness and makes do with many
  overlapping and contradictory assumptions

5
Heuristics and Inferences

• To increase efficiency, special-purpose
  inferences and heuristics are applied
• Temporal reasoning
• Spacial reasoning
• Domain specific axioms (e.g., medical diagnostic
  rules)
• Inferences for specific syntactic structures
• General-purpose axioms to be applied when
  special-purpose axioms are not available or do
  not work

6
Categories

• Categories of categories
• Categories of individuals (objects)
• Categories of intangible objects (information,
  numbers)
• Categories of tangible objects (living things,
  artifacts)
• Categories of scripts (typical actions and
  events)
• broken into physiological actions, problem
  solving actions, communications, rites of
  passage, work, hobby, natural phenomena

7
Other Items Represented

• Predicates (relationships between objects)
• Attributes (of objects)
• Lexical items (words, parts of speech/tense,
  etc)
• Proper nouns (specific people, places, )
• Microtheories
• Miscellany

8
Microtheories/Contexts

• Contexts or microtheories are partitions within
  the KB that describe different domains/problems/co
  ncepts
• Previous KBS have indicated that 10,000 rules is
  about the limit before efficiency and accuracy
  plummet. To get around this, Cyc uses contexts
• Examples might include manufacturing, weather
  during the winter, dining in restaurants, dining
  at home, medical diagnosis, what to look for when
  buying a car, etc

9
More on Contexts

• Each context has its own
• categories (hierarchy of related items)
• predicates (some are shared between contexts,
  however one context may use the same predicate as
  another with different numbers of parameters!)
• axioms/inference methods
• assumptions
• Contexts may overlap or be independent

10
Using Contexts

• Assertions (axioms, statements) are not
  universally true, but only within a given context
• The context is specified in a statement (e.g.,
  ntp naïve theory of physics context which might
  be used to reason over the motion of objects
  without resorting to physics)
• A statement may be true in one context and false
  in another (for instance, an assumption that
  apples cost 30 cents may be false in the context
  of the depression-era US)

11
Decontextualization

• It is necessary sometimes to lift elements from
  one context into another
• This provides a mechanism for reasoning about
  multiple items that are in different contexts
• When lifting items from one context to another,
  assumptions, vocabulary, axioms and other
  elements that differ must be resolved in the new
  context

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Example

• Consier the WorkPlaceCodeofConduct context
• It might state that people dont generally make
  loud noises
• Suppose a person brings a baby to a workplace
• The baby may not remain quiet because the baby
  context differs, but we would not expect the
  babys mother to yell at the baby because the
  mother obeys the WorkPlaceCodeofConduct context
  rules/assumptions

13
Another form of lifting

• Cyc requires a method of translating the
  vocabulary of one context into another
• This form of lifting can change predicates
  (e.g., a binary predicate into a unary predicate)
  or map terms onto other terms
• Default Coreference Rule is a heuristic for
  lifting which assumes that terms are equal in
  different contexts unless specifically noted

14
Cyc Applications

• Person Modeling (autonomous agents, simulations
  of a persons behavior)
• Smart DBs, SSs and WPs
• Information Sharing in KBs and DBs
• Image and Information retrieval
• Semantic file systems

15
Examples of Cyc Abilities

• You have to be awake to eat
• You can usually see peoples noses but not their
  hearts
• You cannot remember events that have not yet
  happened yet
• If you cut a lump of peanut butter in half, each
  half is also a lump of peanut butter, but if you
  cut a table in half, neither half is a table