Scruffy Knowledge Representation Schemes

• Knowledge Graphs (previously "Semantic nets")
  • Introduction from IBM
  • Describe the world in terms of objects (nodes) and binary associations (labelled directed edges).
  • Example: Snow and ice
  • Common associations
    • Classification - instance_of/member_of
    • Aggregation - part_of
    • Generalization - is_a/subset_of
    • Example: My chair
  • Example: Choose a student
  • Richer associations.
    • Any can be made up
    • Hyper-edges for n-ary associations. Example: John gave Mary a book
    • Boxed relations for universal quantification. Double boxed relations for existential quantification. Example: Mary
  • Taking care with object nodes
    • Beware confusing instance_of and subset_of. Example: My chair is a chair
    • Beware confusion with relation on sets and instances, e.g., size_of people
    • Variable values. Example: John is taller than Bill
  • Reasoning
    • Paths between nodes (graph theory :-)
    • Inheritance in is_a and part_of associations. Examples: Ontology, the dog parts, Mary's legs
    • Intersection search. Example: Mary and people
    • Attaching epistemic and assertional status to associations
  • Partitions allow
    • Quantification. Example: The biting dog
    • Meta-statements. Example [ala Lug p.227]
  • Implementation
    • Direct with linked structures
    • Using logic with binary predicates, and having formulae to express hierarchies, etc.
  • Careless use of associations leads to incompleteness (e.g., two labels for the same association).
    • Sets of "adequate" associations have been proposed.
    • Conceptual dependancies use hyper edges and a rich set of associations. Example: John ate the egg. Example: John prevented Mary from giving a book to Bill.
  • Views from neo4j; Wikipedia

• Frames and Property Graphs
  • A way of representing stereotypical objects and situations.
  • A "struct", whose slots may contain
    • Data (possibly a (link to) another frame
    • Default values
    • Constraints
    • Procedures to run when a value is needed, inserted, removed
    • Example: Hotel room
  • Reasoning
    • Default reasoning - slots exist => there exists a value, e.g., a room has a door.
    • Constraints provide information for reasoning, and violations suggest repairs.
    • Attaching epistemic and assertional status to slots
  • Scripts
    • Frames for sequences of events. Example: Restaurant
    • Components
      • Track
      • Props
      • Roles/actors
      • Entry conditions
      • Exit results
      • Scenes
    • Reasoning
      • Examples: Restaurant queries
  • Used as nodes in Knowledge Graphs to form Property Graphs
  • Historical fact: helped produce the notion of OO programming

Exam Style Questions

• Explain how semantic nets and frames can be viewed as different implementations of the same basic knowledge representation schema. Suggest types of knowledge for which each is more suitable.
• Give a property graph representation of the following:

  Billy is a mountain. Ethel is a tree. All mountains have trees growing on them. Billy has one tree growing on him. Ethel grows on Billy.

• Explain what the following are in terms of scripts:
  • Track
  • Props
  • Roles
  • Entry conditions
  • Scenes
  • Results
• Give a script suitable for the typical exam writing event.