---
title: "KR models; semantic nets"
subject: "Artificial Intelligence"
chapter: 5
key: "semester_6/artificial_intelligence:kr-models-semantic-nets"
source: https://www.bctengineer.com/q/semester_6/artificial_intelligence/kr-models-semantic-nets
site: BCT Engineering
---

# KR models; semantic nets

Artificial Intelligence · Chapter 5: Structured Knowledge Representation

- Asked in: 2069 Bhadra, 7 marks
- Video: [Knowledge Representation || Semantic Networks || Frames || Artificial Intelligence(Hindi)#31](https://www.youtube.com/watch?v=nRMLTHDAVqc) — Exam Aasaan Hai !!!
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/artificial_intelligence/kr-models-semantic-nets
- Whole chapter: https://www.bctengineer.com/md/semester_6/artificial_intelligence/chapter-5

## Question

What are the different knowledge representation models? Discuss semantic nets with an example.

## Short answer

Models: logic, rules, semantic nets, frames, conceptual dependency, procedural, probabilistic. A semantic net is a graph with nodes and labeled arcs; inheritance via is-a. Example: Person has-part Head; Student is-a Person; Rani instance Student, thus inherits head.

## Answer

**Knowledge representation (KR)** is the way facts about the world are encoded so that a program can store them and reason with them. A good scheme should have representational adequacy, inferential adequacy, inferential efficiency and acquisitional efficiency (Rich & Knight).

#### Knowledge representation models
1. **Logical representation:** propositional logic and predicate logic (FOPL). Precise semantics and sound inference (e.g. resolution), but can be inefficient. Example: ∀x man(x) → mortal(x).
2. **Production rules:** IF condition THEN action. Used in expert systems; modular and easy to explain. Example: IF fever AND rash THEN measles.
3. **Semantic networks:** graph of nodes and labelled arcs with inheritance.
4. **Frames:** slot-and-filler structures with defaults and procedures.
5. **Conceptual dependency (scripts):** language-independent meaning using primitive acts; scripts describe event sequences (restaurant script).
6. **Procedural representation:** knowledge embedded as procedures or programs (e.g. Prolog clauses, LISP functions).
7. **Probabilistic / fuzzy models:** Bayesian networks, fuzzy sets for uncertain knowledge.

#### Semantic nets
A semantic net is a labelled graph: nodes are objects or concepts, arcs are relations (`is-a`, `instance`, `has`, `colour`). Properties are inherited through `is-a` links.

Example: "Rani is a student. A student is a person. A person has a head. Rani studies at Pulchowk."
```text
 [Person] --has-part--> [Head]
    ^ is-a
 [Student]
    ^ instance
 [Rani] --studies-at--> [Pulchowk]
```
Query "Does Rani have a head?" is answered by moving Rani → Student → Person → Head.

**Advantages:** easy to understand, supports inheritance, compact. **Limitations:** no standard meaning for links, weak for negation, quantifiers and exceptions, and large nets are hard to manage.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which list contains only knowledge representation models?
   A. Selection, crossover, mutation, fitness, population
   B. Modus ponens, resolution, unification, backtracking, Skolemisation
   C. Logic, production rules, semantic nets, frames, conceptual dependency
   D. Supervised, unsupervised, reinforcement, rote, analogy
   Answer: C. These are the standard KR schemes; the others are GA operators, inference techniques and learning types. (Key point: Models)

2. What form do production rules take?
   A. IF condition THEN action
   B. Node --relation--> node
   C. Slot: value with facets
   D. Primitive act with actor and object
   Answer: A. Production rules are IF-THEN pairs used in expert systems. (Key point: Production rules)

3. How is 'Does Rani have a head?' answered in the net?
   A. Look for a direct arc from Rani to Head only
   B. Move Rani → Student → Person → Head via instance and is-a links
   C. Resolve the query with the negated goal
   D. Compute it with an if-needed procedure
   Answer: B. Head is attached to Person and inherited down. (Key point: Rani example)

## Related in Artificial Intelligence

- [Frames and semantic nets importance](https://www.bctengineer.com/question.md?key=semester_6%2Fartificial_intelligence%3Aframes-and-semantic-nets-examples) — Artificial Intelligence, chapter 5, asked 3×
- [Semantic nets with example](https://www.bctengineer.com/question.md?key=semester_6%2Fartificial_intelligence%3Asemantic-net-with-example) — Artificial Intelligence, chapter 5, asked 3×
- [Frame vs semantic net](https://www.bctengineer.com/question.md?key=semester_6%2Fartificial_intelligence%3Aframe-vs-semantic-net) — Artificial Intelligence, chapter 5
- [Knowledge, reasoning; forward chaining](https://www.bctengineer.com/question.md?key=semester_6%2Fartificial_intelligence%3Aforward-chaining-kr-reasoning) — Artificial Intelligence, chapter 4