2. Representation and Mapping
- Mapping is the process that maps facts to representations and vice versa.
- Forward mapping : facts to representation
- Backward mapping : representation to facts
Facts
Internal
Representation
English
Representation
English GenerationEnglish Understanding
3. Properties of Good Knowledge
Representation
1. Represential Adequacy : Ability to represent all knowledge needed in the
domain
2. Inferential Adequacy : Ability to manipulate knowledge to derive new
structures inferred from old
3. Inferential Efficiency : Ability to perform inference in the most efficient
directions
4. Acquisitional Efficiency : Ability to acquire new information easily
4. Semantic Nets
- Graphical representation of knowledge in terms of nodes and the arcs
connecting them
- Nodes represents objects
- Arcs represent links or relationships
5. Semantic Nets (Example)
Knowledge base:
1. Tom is a cat
2. Tom caught a bird
3. Tom is owned by John
4. Tom is ginger in color
5. Cats like cream
6. The cat sat on the mat
7. A cat is a mammal
8. A bird is an animal
9. All mammals are animals
10.Mammals have fur
7. Semantic Nets (Advantage)
- Natural and modular
- Efficient, simple and understandable
- Translatable to PROLOG without difficulty
- Meaning is simple to generate
8. Semantic Nets (Disadvantage)
- No standard definition
- Not intelligent
- Depends on the designer
- Creates confusion on same network created by multiple people
- Nodes representing class and object look same
- Negation and Disjunction can not be expressed easily
9. Frames
- Schema representation that provides structure for knowledge
representation
- Contains frame name, slots and slot fillers.
- Slots correspond to fields and fillers correspond to values.
- Frame provides 3D representation of knowledge to semantic nets by
allowing nodes to have structure
11. Conceptual Dependency
- 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
- Agents and objects are represented
- ATRANS, PTRANS, MTRANS, MBUILD, SPEAK, ATTEND, PROPEL, MOVE,
GRASP, EXPEL, INGEST
13. Script
- Structured representation describing a sequence of events in a particular
context
- Extended frames by representing expectations of actions and state changes