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