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Notes of Artificial Intelligence [CT 653]

Structured Knowledge Representation


Representation and Mapping

- Mapping is the process that maps facts to representations and viece versa. The forward representation mapping maps from facts to representation mapping maps from facts to representations while the backward representation mapping maps from representations to facts.
- It shows the relationship between the objects.


Approaches to Knowledge Representation

A good knowledge representation system should have following properties:
a) Representable adequacy -> ability to represent all knowledge needed in the domain.
b) Inferential adequacy -> ability to manipulate knowledge to drive new structures inferred from old.
c) Inferential efficiency -> ability to perform inference in the most efficien directions
d) Acquisitioned efficiency -> ability to acquire new information easily.

Types of Knowledge:

a) Simple relational knowledge [facts as set of relations)
b) Inheritable knowledge(as a desired inference mechanism
c) Inferential knowledge(as a formal logic)
d) Procedural knowledge(control information within the knowledge)

Issues in Knowledge Representation


- Are there any attributes of object that occurs in almost every problem domain?
- Are there any imp relationships between attributes of objects?
- At what level should knowledge be represented?
- How should sets of objects be represented?
- How can relevant parts be accessed when needed.

Types of knowledge model

a) First order predicate logic
b) Procedural representation model
c) Relational representation model
d) Hierarchical representation model

Semantic nets and frames

Semantic Nets

- Semantics nets is the graphical representation of knowledge in terms of nodes and the arcs connecting them.
- Nodes represents objects; arcs represents the links.
- Links are used to express relationships
- Links are of two types: is –a and a- kind-of
- Is-a refers to specific member of a class.
- A-KIND-OF relate one class to another.


- Frame is a type of schema used in AI that provides a convenient structure for knowledge representation.
- Frame Is similar to field-value structure corresponding slots and slot fillers
- It is a collection of slots and fillers that defines an objects
- Frame provides a third dimension representation of knowledge to semantic nets by allowing nodes to have structures

- Eg: a frame for a book node is

Slots fillers
Publisher mcgraw
Title AI
Author rich
Edition third
Year 1998
Pages 500
Price 200


Q) Declarative knowledge base is:
- A person is a mammal
- Sakti Gauchan is a person
- Person has nose
- Sakti gauchan is in Nepalese team.
- Uniform color of sakti gauchan is Red/blue

Draw the semantic net representation.



Conceptual Dependencies and Scripts

Conceptual dependency (cd)

- Cd is used to represent knowledge acquired from natural language input
- If two or more sentences are identical in meaning, there should be only one representation
- Sentences are represented as a series of diagrams depicting actions using both abstract and real physical situations.
- The agents and objects are represented.

- Eg:
--transfer of abstract relationship eg: give take etc.
Mary take a book from john
John gave Mary a book



- Script is a structured representation describing a sequence of events in a particular context
- Script is the extended frames by representing expectations of actions and state changes.

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