USING ISTAR - FOR SEMANTIC NETS

In the previous chapter, we have concentrated on inference nets; now we 
turn to semantic nets which, in the simple form supported by Istar, are 
like the Mind Maps common in the decision support arena.  Istar isn't yet 
ideal for these, but can still be very useful.

      A semantic net is a collection of items linked with relationships.
The formalism was originally proposed in the artificial intelligence 
community in the 1970s as an aid to storing sentences on computer: each 
piece of the sentence was an item, and various relationships held them 
together to make the whole text.  But today semantic nets are seen more as 
a flexible kind of data storage.  Istar offers some, but not all, of this 
flexibility.

      For semantic nets items and relationships are all important;
attributes are less important.  So we need to create new types of 
relationship and item for use in our net.  But, after reading Using Istar - 
For Inference, you should have enough experience of Istar to be able to do 
this by yourself after reading the Panels chapter, in its sections on 
creating new item and relationship types.  So, instead of step by step 
instructions on how to create these, we will look at an example.  (This 
part of the tutorial applies only to versions 1.03 and later.)

#  Load the 'Philosophy' knowledge base and examine it.  It portrays some 
of the flow of philosophical thought up to the time just before the 
Reformation and Renaissance, as a semantic net.  The net is based on, and 
is my interpretation of, Survey of the History of Philosophy, classroom 
teaching notes by John Van Dyk, Professor of Philosophy, Dordt.

#  It shows many of the major Western philosophers and how they influenced 
each other's thinking.  Each has a name, a date and, as meaning, a brief 
description of their philosophical stance.  Move the mouse around to see 
their stances.  (The item type, Philosopher, was created for this KB by 
hitting the 'New' button beneath the item types list on the KB panel.)

#  There is an 'Influence' relationship linking some of them.  This shows 
that, for instance, the thinking of Socrates influenced the thinking of 
both Plato and the Cynics.  (This type of relationship was created 
specially for this KB, using the 'New' button below the relationship types 
list on the KB panel.)

#  Some influence links are a different colour; they show a negative 
influence, in that the later thinking reacted against the earlier and 
developed in an opposing direction.  For instance, Tertullian called Plato 
"the father of all error".

#  Peruse the whole KB, and see what you pick up about philosophers and how 
Western thinking developed up to the Middle Ages.  Alter things if you 
disagree with them.

#  It is often useful to see the consequents or antecedents of a given 
thing.  Move over to the right and place the mouse cursor over the name box 
of Tertullian.  Press the 'A' key (A for antecedent; before version 1.06, 
press the * key on the numeric pad instead; it was changed to 'A' because 
some Amigas did not have that key, and to make it a bit easier to remember 
wbich key to press).  You will see most of the net disappear, showing only 
those philosophers and streams of thought that contributed to Tertullian's 
thought (i.e. were antecedent to it).

#  Notice how Tertullian reacted against Plato (negative link), but at the 
same time was positively influenced by the Stoics, who were themselves 
positively influenced by Plato.  This sounds like a contradiction - when, 
from one box to another, you have two paths of which one is negative and 
one is positive.  It is not necessarily so, since Tertullian probably 
absorbed some Platonic ideas while rejecting others.

#  Now move the mouse cursor over Plato and press the 'C' key (C for 
consequents; not available before version 1.06).  The net shows now all 
those philosophers and philosophical systems that have been influenced by 
Plato, either directly or indirectly - very many of them.

#  Notice four things.

#  First, notice how you do actually learn something new by persuing the 
KB; it is like a book.  (But, in this basic version, don't expect to learn 
too much!)

#  Second, notice how certain items, such as Plato and Aristotle, have many 
(consequent) relationships; their influence in philosophy is acknowledged 
to be great.  A high branching factor is a visual indication that an item 
is a key item in the domain of knowledge.

#  Third, if you know something of philosophy, you might wonder whether 
some links are missing; some undoubtedly are, but notice how it has 
stimulated you to think - a form of knowledge refinement mentioned above.

#  Fourth, many of the terms you will not understand.  In a mind map this 
can be a problem, so when you make up a mind map, think about how to make 
things more understandable.

      The Philosophy KB bundled with version 1.03 and later of Istar is
fairly basic, and will hopefully be extended in the near future, especially 
to use Topics.


Copyright (c) Andrew Basden, 1996, 1997.
