flex Expert System Toolkit - LPIS

2. Frames and Inheritance 12
2. Frames and Inheritance
In this chapter we describe the frame sub-system of flex. This includes the
form and content of individual frames, how frames are linked together to
form a frame hierarchy, and how values are inherited through that
hierarchy.
What is a Frame ?
A frame is similar to an object and is a complex data structure which
provides a useful way of modelling real-world data objects.
Frames are analogous to records within a database but are far more
powerful and expressive. Each individual frame has a name by which it is
referred, details of its parent(s) frame, and a collection of slots or attributes
(similar to fields within records) which will contain values or pointers to
values. Slot values can be explicitly defined locally, or implicitly inherited
from an ancestor frame further up the hierarchy.
Frame
motions
habitat
skin
bird
fly
tree
feather
Name
Slots
Flex has its own language (for representing frames and other constructs)
called the Knowledge Specification Language. For example, the KSL code
for the above frame could be:
frame bird
default skin is feather and
default habitat is a tree and
default motions are { fly } .
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