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Frame Knowledge Representation

 

Consider the example first discussed in Semantics Nets (Section 6.2.1):

 
Person

isa:    Mammal

Cardinality: tex2html_wrap_inline7166

Adult-Male

isa: Person

Cardinality: tex2html_wrap_inline7166

Rugby-Player

isa: Adult-Male

Cardinality: tex2html_wrap_inline7166

Height:

Weight:

Position:

Team:

Team-Colours:

Back

isa: Rugby-Player

Cardinality: tex2html_wrap_inline7166

Tries:

Mike-Hall

instance: Back

Height: 6-0

Position: Centre

Team: Cardiff-RFC

Team-Colours: Black/Blue

Rugby-Team

isa: Team

Cardinality: tex2html_wrap_inline7166

Team-size: 15

Coach:

  figure789
Figure: A simple frame system

Here the frames Person, Adult-Male, Rugby-Player and Rugby-Team are all classes and the frames Robert-Howley and Cardiff-RFC are instances.

Note

DISTINCTION BETWEN SETS AND INSTANCES

It is important that this distinction is clearly understood.

Cardiff-RFC can be thought of as a set of players or as an instance of a Rugby-Team.

If Cardiff-RFC were a class then

Instead we make it a subclass of Rugby-Player and this allows the players to inherit the correct properties enabling us to let the Cardiff-RFC to inherit information about teams.

This means that Cardiff-RFC is an instance of Rugby-Team.

BUT There is a problem here:

This is why we need to view Cardiff-RFC as a subset of one class players and an instance of teams. We seem to have a CATCH 22. Solution: MetaClasses

A metaclass is a special class whose elements are themselves classes.

Now consider our rugby teams as:

  figure837
Figure: A Metaclass frame system

The basic metaclass is Class, and this allows us to

Inheritance of default values occurs when one element or class is an instance of a class.

Slots as Objects

How can we to represent the following properties in frames?

A slot is a relation that maps from its domain of classes to its range of values.

A relation is a set of ordered pairs so one relation is a subset of another.

Since slot is a set the set of all slots can be represent by a metaclass called Slot, say.

Consider the following:

 
SLOT

isa: Class

instance: Class

domain:

range:

range-constraint:

definition:

default:

to-compute:

single-valued:

Coach

instance: SLOT

domain: Rugby-Team

range: Person

range-constraint: tex2html_wrap_inline7290 (experience x.manager)

default:

single-valued: TRUE

 
Colour

instance: SLOT

domain: Physical-Object

range: Colour-Set

single-valued: FALSE

Team-Colours

instance: SLOT

isa: Colour

domain: team-player

range: Colour-Set

range-constraint: not Pink

single-valued: FALSE

Position

instance: SLOT

domain: Rugby-Player

range: { Back, Forward, Reserve }

to-compute: tex2html_wrap_inline7290 x.position

single-valued: TRUE

NOTE the following:


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dave@cs.cf.ac.uk