4.12 Semantic networks, extended semantic networks and frames

Work through these

• Represent concepts, semantic relationships and property links

  A network of concepts joined by labelled relationships, with links carrying properties. It is one of the oldest representations and its readability is its main virtue.

• Build a semantic network from a paragraph of English

  Building a network from ordinary English is the exercise that shows how much of a sentence is relationships rather than words. It also shows how much ordinary language leaves implicit.

• Use inheritance through is-a links, and show where it goes wrong

  Properties passed down a hierarchy save enormous repetition and break on exceptions, which is where the classic examples about flightless birds come from. Handling exceptions is the hard part.

• Extend a semantic network to handle quantification and negation

  Ordinary networks cannot express statements about all or none of something, and the extended form adds machinery for it. Knowing the limitation is what motivates the extension.

• Represent the same domain with frames, slots and defaults

  A frame groups everything known about a concept into named slots with default values, which is closer to how an object is described in programming. Comparing the same domain in both notations is instructive.

• Compare all three on the four adequacy properties

  Setting all three representations against the four adequacy properties, which is what turns a tour of notations into a judgement. This comparison is a standard examination question.