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Knowledge Representation

Knowledge Representation. Introduction. Domain specific knowledg e is needed to solve some problems. Knowledge base – representation. Inference techniques Use to prove facts. Use to answer queries. Knowledge Representation Schemes.

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Knowledge Representation

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  1. Knowledge Representation

  2. Introduction • Domain specific knowledge is needed to solve some problems. • Knowledge base – representation. • Inference techniques • Use to prove facts. • Use to answer queries

  3. Knowledge Representation Schemes • Logical representation schemes – logical proofs, e.g. predicate logic. • Procedural representation schemes – procedural list of instructions, e.g. production rule systems. • Network representation schemes – graphical representation, e.g. semantic networks and conceptual graphs. • Structured representation schemes –extension of network schemes, e.g. scripts and frames. • Structures for incomplete or inconsistent knowledge: Bayesian reasoning, Dempster-Shafer, fuzzy logic. .

  4. Semantic Networks • Consists of nodes and arcs. • Nodes represents objects. • Arcs represents relationships between the objects. • Relationships: • is-a • Instance • has/has-a • Others .

  5. Example 1 Clyde is an elephant. .

  6. Example 2

  7. Example 3

  8. Example 4 John’s height is 72. John is taller than Bill.

  9. Example 5 John gives Mary the book.

  10. Using Case Frames • Problems with semantic networks • Attempts to standardize semantic networks led to the development of case frames. • Each sentence is represented by a case frame. • Each case frame represents an actions. • Case frames define case relationships: agent, object, instrument, location and time. .

  11. Example: Case Frame

  12. Exercises Construct semantic networks for the following statements: • Pompeian(Marcus), Blacksmith(Marcus). • Mary gave the green coloured vase to her favorite cousin. • John went downtown to deposit his money in a bank.

  13. Conceptual Graphs • Is a connected bipartite graph. • Conceptual relation nodes represent relations between concepts. • The arcs connecting nodes are not labeled. • Concepts are represented by boxes. • Relations are represented by arcs.

  14. Conceptual Graph Relations

  15. Example Mary gave John the book.

  16. Unique Markers • If an individual object is unknown a unique marker can be used in place of the name of the object. • A unique marker is comprised of a hash symbol (#) followed by a number. • Each object has its own unique marker.

  17. Example 1: Unique Markers

  18. Example 2: Unique Marker

  19. Example Her name was McGill and she called herself Lil, but everyone knew her as Nancy.

  20. Generic Markers • A generic marker is used to represent an unspecified individual of a type. • A generic marker is represented by an asterisk *. • Name variables can also be used, e.g., *X to indicate an unspecified individual.

  21. Example: Generic Marker The dog is scratching its ear with its paw.

  22. Display Form John is going to Boston by bus.

  23. Linear Form John is going to Boston by bus. [Go] – (Agnt) → [Person: John] (Dest) → [City: Boston] (Inst) → [Bus]

  24. Exercises Construct conceptual graphs for the following statements: • Jane gave Tom an ice cream. • Basketball players are tall. • Paul cut down the tree with an axe. • Place all the ingredients in a bowl and mix thoroughly.

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