mops.lisp is an implementation of a simple hierarchical frame memory, such as that used for implementing Schank's Memory Organization Packets (MOPs).

A frame is a very general data structure, useful for representing different kinds of knowledge, including concepts, abstractions, indices, and so on. This package provides the basic functionality of frames, for use and extension by other packages.

A frame represents a concept. Each frame has

The slots give information about attributes of name} and have roles, e.g., color with fillers, e.g., grey. Fillers are often the names of other frames.

Here are examples of three very different concepts being represented, a concrete object, an abstraction, and an event involving the object:

clyde-1
  absts: elephant
  slots:
    name = Clyde
    age = 15
elephant
  absts: mammal
  slots:
   color = grey
event-1
  absts: event
  slots:
    actor = clyde-1
    action = ingest
    object = peanuts-1

The chain of links from a frame to its immediate abstractions, and from the immediate abstractions of their abstractions, and so on, forms an abstraction hierarchy. For example, we might have the hierarchy "clyde is an elephant, an elephant is a mammal, a mammal is an animal, and an animal is a thing."

Using the code in mops.lisp, the simple examples above could be defined as follows:

(definstance clyde-1 (m-elephant) :age 15 :name clyde)

(defmop m-elephant (m-mammal) :color grey)

(definstance event-1 (m-event)
   :actor clyde-1
   :action m-ingest
   :object peanuts-12)

A frame can have more than one abstraction, e.g., if clyde-1 performed in a circus, we might write:

(defmop clyde-1 (elephant circus-performer) ...)

MOP Functions

The following briefly describes the functions defined in mops.lisp.

(defmop name abstractions role1 filler1 role2 filler2 ...) => name
(definstance name abstractions role1 filler1 role2 filler2 ...) => name
(add-frame name :type type :abstractions abstractions :slots slots)
(add-instance name slots) => name

defmop defines a MOP abstract concept. definstance defines an instance of a MOP. add-instance is the function for adding an instance that code such as a parser would call to make instances on the fly.

The name can be any Lisp symbol. abstractions should be a list of names of other MOPs. Each role should be a symbol, and by convention, keywords are used. For instances, filler is either a number, string, or name of a MOP or instance. For MOPs, the full form of a filler is a list of the form (:filler value :constraint constraint). The value can be a number, string, or name of a MOP or instance, and is a default value to be inherited by instances of this MOP. The constraint can be a MOP and is a type-constraint. Both :filler value and :constraint constraint are optional. The form (:filler value) can be given as just value, as in instances.

For example, to define an elephant, with default color grey and color constrained to be some instance of color:

(defmop m-elephant (m-animal)
    :color (:filler grey :constraint m-color))

The core underlying function is add-frame. This is used by the other functions to construct the internal frame structure and insert it into the abstraction hierarchy. It takes a name for the MOP or instance plus the following keyword parameters:

(mop-p name) => true or false
(instance-p name) => true or false

mop-p and instance-p test if name names a MOP or MOP instance, respectively.

(find-instances name slots) => list of instances

Returns all instances of name with slots whose fillers are equal to or specializations of the corresponding fillers in slots. slots has the form (role1 filler1 role2 filler2 ...). Example call:

(find-instances 'animal (list :color gray))

(frame-of name) => frame or nil
(->frame name) => frame

These both return the internal frame for a name. -> will create one if it doesn't exist.

(absts-of name) => list of names
(slots-of name) => list of slots
(all-absts-of name) => list of names

absts-of and slots-of return the abstractions and slots explicitly defined for a MOP. all-absts-of returns the linearization of all the abstractions of name, including name}, with no duplicates, sorted by specificity, with the most specific item first.

(abstp abst spec) => true or false

abstp returns true if abst is either eql to or some abstraction of spec. Non-frames, such as numbers and strings, are abstractions of themselves.

(slot-role slot) => slot name
(slot-filler slot) => slot filler
(role-filler name role) => filler
(inherit-filler name role) => filler
(<- name role1 role2 ...) => filler

These are the basic functions for accessing fillers of slots in a frame. slot-role and slot-filler operate on the slot objects returned by slots-of. More commonly, you use role-filler to get the filler, if any, of role in the frame name. inherit-filler is like role-filler but searches the abstraction hierarchy. <- -- not to be confused with backward chaining -- does a sequence of inherit-filler's. For example (<- 'event-1 :actor :age) would get the age of the actor of event-1.

(clear-memory)
(show-frame name)
(show-memory [name stream slots-p])

clear-memory erases all frames from memory. show-frame displays a MOP in readable form. show-memory shows all the frames in memory, in tree form. If name is given, only that MOP and its children are shown. If stream is given, output is to that stream, rather than *standard-output*. If slots-p is true, the slots of each frame are shown.

Faculty: Chris Riesbeck
Time: Monday, Wednesday, Friday: 1pm - 2pm
Location:Annenberg G15

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