flex Expert System Toolkit - LPIS

2. Frames and Inheritance 24
Depth-First versus Breadth-First Search ?
The frames to be considered, when looking for a potential place to inherit
from, are determined by the frame hierarchy and the attribute in question.
Whenever there are alternative places to search, there are inevitably
alternative ways of looking.
In both of the following methods, the search is left-to-right over the ordering
of parent-frames.
A depth-first search of the frame hierarchy will investigate a complete
ancestor branch before considering alternative ancestor branches.
For example, a depth first search of the example hierarchy, starting at
Sammy, will visit the following frames in order :
4
Animal
3
Mammal
Carnivore
5
2
Feline
1
Cat
Sammy
1 Cat being the parent-frame of Sammy
2 Feline being a grandparent-frame
3 Mammal being the first great-grandparent-frame
4 Animal being a great-great-grandparent-frame
5 Carnivore being the second great grandparent-frame
A breadth-first search, however, will visit all frames at a particular ancestor
level before considering any at a higher level. It will visit all parent-frames
first, then all grandparent-frames, all great-grandparent-frames, and so on.
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