flex Expert System Toolkit - LPIS

7. Knowledge Specification Language 82
Frames
flex toolkit
There are three parts to the definition of a frame:
1. The first part of a frame specifies whereabouts in the hierarchy of frames it
exists, by specifying its parent frames (if any). The frame hierarchy
determines how attributes are inherited.
2. The second part of a frame is optional and specifies what the default
attributes of a frame are. The defaults remain throughout the life-span of the
frame, and are used in the absence of any current value being assigned.
3. The third and final part to a frame is also optional and represents a
refinement of the inheritance hierarchy. Alternative parent frames can be
nominated for the inheritance of specific attributes, or specific attributes may
be declared not to be inherited.
The general format of a frame is as follows.
frame Name
default Attribute1 is Value ;
inherit Attribute2 from Frame .
The simplest example of a frame is a declaration of the frame’s name only.
Example
frame toy .
To this may be added some default values for its slots.
Examples
frame picture
default colour is red and
default shape is oval and
default pen_size is thin and
default link is arrow.
frame text_spec
default size is 12 and
default font is 'Courier' and
default style is normal.
frame computer
default memory is 24 and
default disk is 500 and
default accessories are
{ monitor and keyboard and mouse } and
default speed is 66.
To specify the parents of a frame, use the keywords
is a