Approaches to Knowledge Representation

Simple relational knowledge

The simplest way of storing facts is to use a relational method where each fact about a set of objects is set out systematically in columns. This representation gives little opportunity for inference, but it can be used as the knowledge basis for inference engines.

• Simple way to store facts.
• Each fact about a set of objects is set out systematically in columns (Fig. 7).
• Little opportunity for inference.
• Knowledge basis for inference engines.

Figure: Simple Relational Knowledge

We can ask things like:

• Who is dead?
• Who plays Jazz/Trumpet etc.?

This sort of representation is popular in database systems.

Inheritable knowledge

Relational knowledge is made up of objects consisting of

• attributes
• corresponding associated values.

We extend the base more by allowing inference mechanisms:

• Property inheritance
• elements inherit values from being members of a class.
• data must be organised into a hierarchy of classes (Fig. 8).

Fig. 8 Property Inheritance Hierarchy

• Boxed nodes -- objects and values of attributes of objects.
• Values can be objects with attributes and so on.
• Arrows -- point from object to its value.
• This structure is known as a slot and filler structure, semantic network or a collection of frames.

The algorithm to retrieve a value for an attribute of an instance object:

1. Find the object in the knowledge base
2. If there is a value for the attribute report it
3. Otherwise look for a value of instance if none fail
4. Otherwise go to that node and find a value for the attribute and then report it
5. Otherwise search through using isa until a value is found for the attribute.