flex Expert System Toolkit - LPIS

2. Frames and Inheritance 22
Inheriting Values through the Frame Hierarchy
In earlier sections we discussed frames and their possibility for distributing
information. In this section we shall discuss in more detail exactly how the
distributed information passes from one frame to another.
In general, information flows down the frame hierarchy from those at the
top to those at the tips. This is accomplished by inheritance.
Whenever there is a request for the some slot value, the inheritance
algorithm is automatically invoked. The most obvious place to look first is in
the original frame itself, since it may have either a current or a default value
for the required attribute. Only if such a value does not exist locally will it be
necessary to look elsewhere.
Where to look, in which order to look and when to stop looking are the
subject matter of the following sections. We shall use the following example
hierarchy to illustrate the different methods.
Example
flex toolkit