Page 162 - DCAP310_INTRODUCTION_TO_ARTIFICIAL_INTELLIGENCE_AND_EXPERT_SYSTEMS

Introduction to Artificial Intelligence & Expert Systems

Notes pointers (links) to other Frames
ako (a-kind-of)
instance (is-a)

Instantiation Procedure
Inheritance Procedure
Default Inference Procedure
Consistency Checking Procedure

Inconsistency Resolution Procedure

Notes That knowledge is organized around the objects. The knowledge is accessed when
an instance of a particular object is created or instantiated. Instantiation can be an extremely
rich and complicated procedure as can be noted by reviewing the various procedures that
are listed above as part of the instantiation procedure. Additionally, instantiation is typically
specialized with respect to classes of objects.

An Example

A brief example of an instantiation process is shown below. This example is a trace recorded
long ago (in the late 70s or early 80s) taken from a frame system, AIMDS, developed for use in
research on plan recognition. For those unfamiliar with programming, most programming
languages give one some facility create a record of chosen aspects of a procedure. In this example,
certain component functions of the process were chosen and the result returned by these
component function is printed as the function is exited.
In this particular example, the instantiation process is specialized for frames that represent
actions which modify a world. The example below lists the definition provided the system for
the two frames used in this example. The first is the frame referred to as ACT. The second is the
frame referred to as WALK. WALK is a kind of ACT. When a WALK is instantiated an ACT
representation is also created for that instance of ACT. In this example, we will focus on the
frame, WALK. The strings TDN: and QSCC: that occur in these tables are simply the name of
functions that are invoked to create these data structures when this knowledge is entered.
Beneath the name of the frame is listed the set of slots that are associated with the frame. For
WALK, the first slot is (AGENT PERSON) the next (LOC LOCATION) and so on. The terms
shown in bold (PERSON, LOCATION, and so one) are other frames which themselves would
typically be further defined. The term proceeding these is the name of the relation or slot
AGENT and LOC in these first two elements. Thus, this is a way of specifying that WALK is a
kind of ACTION which involves an agent who is a PERSON, and so on.
An Example Pair of Frames: ACT and WALK
(* STRUCTURAL DESCRIPTION OF THE ACT FRAME *)
(TDN: [(ACT D)
((PRESUPPOSITIONS L) PROPOSITION)
((RESULTS L) PROPOSITION)
((OUTCOMES L) PROPOSITION)
((PRECONDITIONS L) PROPOSITION)
((ENABLE L) ACT ENABLEDBY)
((MOTIVATES L) ACT MOTIVATESOF) ])

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