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4.4 Qualitative Process
The qualitative process reasoning proposed by Forbus describes physical
phenomenon as some related processes. Each process is described as a set of
individuals, preconditions, quantity conditions, parameter relations and
influences. Reasoning process sequentially chooses some useful processes from
the known process table to describe a physical phenomenon. Following is the key
idea about qualitative physics in qualitative process theory:
(1) The organizational principle is the physical process. Ontology plays an
important role in the organization of knowledge. The physical process is very
intuitive when people carry out reasoning on physical system. So it is sound
to organize the theory in physical field with it.
(2) Express number value with the sequence relation. The important property
difference often comes from comparing. For example, flowing is produced
when the pressure and temperature are different, phase transformation occurs
when temperature reaches a certain critical value, etc. Under many
circumstances, it is more natural to express number value with a set of
ordinal relations.
(3) The single assumption mechanism. The physical process is regarded as the
mechanism to produce variation. So any variation must be interpreted as the
direct or indirect influence of some physical processes. Process ontology has
laid the foundation in the causality of the qualitative physical theory.
(4) Combined qualitative mathematics. When people carry out reasoning on
complicated systems, part of information is used and combined up.
(5) Clear expression and reasoning on model assumption. Clearly expressing the
applicable condition of some particular knowledge and modeling particular
system from field theory have become the central tasks of qualitative physics.
The variation of a physical system is caused by process. A physical process is
described with some processes. That is the basic idea of qualitative process
reasoning approach. Following introduces the description of quantity space and
process in qualitative process reasoning.
1. Quantity Space
(1) Time is expressed by intervals. The relations between intervals are before,
after and equal. Two intervals can be joined. Moment is regarded as
extremely short, whose duration is zero.
