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Knowledge representation > Chapter 2 > Flashcards

Chapter 2 Flashcards

1
Q

Thinking

A

Can be understood as drawing conclusions from a large collection of sentences called a knowledge base (KB)

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2
Q

Sentences

A

Uninterpreted symbolic structures

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3
Q

Symbolic manipulation

A

Computational procedure that involves the manipulation of symbolic structures (sentences) representing propositions.

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4
Q

Back-chaining

A

One example of symbolic manipulation

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5
Q

Knowledge base

A

Collection of sentences

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6
Q

Atomic sentences

A

Simple basic sentences

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7
Q

Conditional sentences

A

Sentences of the form : if P1 and …. and Pn then Q, where Pi and Q are atomic sentences

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8
Q

What do atomic and conditional sentences contain?

A

Variables, constants and special keywords (such as “if”, “and”, “then”..)

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9
Q

Logical entailment concept

A

A sentence cannot not be true if all sentences in the knowledge base are true.

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10
Q

Steps to check for logical entailment:

A
  1. Try to locate Q itself in the KB. If you can, return success.
  2. Otherwise, try to locate a conditional sentence of the form: if P1 and … and Pn, then Q, in the KB. If you cannot, return fail.
  3. Otherwise, use back-chaining to try to establish P1 and P2 and … Pn. If these are all successful, then return success.
  4. Otherwise, go back to step 2 and look for another conditional.
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11
Q

Back-chaining

A

Receives an atomic sentence (the query) as input and its job is to determine if the query is logically entailed by the KB

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12
Q

Even if a query Q can be successfully established, will it be added to the KB?

A

No, because back-chaining always leaves the KB unchanged

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13
Q

Think of an example of a sentence in a KB that includes variables.

A

If X is a child of Y, then Y is a parent of X.

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14
Q

Tracing

A

Simulation fo the execution of the back-chaining procedure

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15
Q

In Prolog, is it important to know what the symbols mean?

A

No, it isn’t.

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16
Q

In Prolog, is it important to keep track of your place in the procedure?

A

Yes, it is.

17
Q

What tracing is used in Prolog to keep track of how deep we are in the procedure?

A

Indentation

18
Q

What is the goal of back-chaining when the query Q only contains constants?

A

The goal is to establish whether Q is logically entailed by the KB

19
Q

What is the goal of back-chaining when the query Q contains variables?

A

The goal is to establish for what values of the variable the query Q is logically entailed by the KB

20
Q

Can we perform “variable renaming” in Prolog?

A

Yes, since the names of the variables do not really matter.

21
Q

What happens when there is a query with variables?

A

The variables in the sentences of the KB are renamed to ensure that they differ from the ones in the query

22
Q

Back-tracking

A

The process of going back and reconsidering the choice of values for variables if things do not work out.

23
Q

Is it possible to have no variables in a top-level query, but to have variables in subqueries?

A

Yes, it is

24
Q

Difference between back-chaining and forward-chaining

A

Back-chaining: only works with KBs with atomic and conditional sentences.
Forward-chaining: starts from atomic sentences and draws new conclusions

25
Q

Is back-chaining goal directed?

A

Yes, it starts with a goal and works “its way” towards what is known (the sentences in the KB)

26
Q

Is back-chaining always logically sound?

A

Yes, it never makes mistakes (so far)

27
Q

Is back-chaining always logically complete?

A

No. It is logically complete UNLESS it gets stuck in a loop

28
Q

To be logically complete

A

Any time a query is logically entailed by the knowledge base, the procedure will eventually return success.

29
Q

Is Prolog based on back-chaining or forward-chaining?

A

Back-chaining

30
Q

What kinds of sentecens cause looping?

A

Sentences in the KB that do not add anything to the KB. An example of such sentences are tautologies.

Knowledge representation (7 decks)

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