FREE online courses on Expert Systems - Data Representation
For all rule based systems, the rules refer to data. The data
representation can be simple or complex, depending on the problem. The four
levels described in this section are illustrated in figure 1.3.
The most fundamental scheme uses attribute-value pairs as
seen in the rules for identifying birds. Examples are color-white, and
size-large.
When a system is reasoning about multiple objects, it is
necessary to include the object as well as the attribute-value. For example the
furniture placement system might be dealing with multiple chairs with different
attributes, such as size. The data representation in this case must include the
object.
Once there are objects in the system, they each might have
multiple attributes. This leads to a record-based structure where a single data
item in working storage contains an object name and all of its associated
attribute-value pairs.
Frames are a more complex way of storing objects and their
attribute-values. Frames add intelligence to the data representation, and allow
objects to inherit values from other objects. Furthermore, each of the
attributes can have associated with it procedures (called demons) which are
executed when the attribute is asked for, or updated.
In a furniture placement system each piece of furniture can
inherit default values for length. When the piece is placed, demons are
activated which automatically adjust the available space where the item was
placed.
