Conceptual Dependency (CD) is a content theory of how to represent simple sentences. Since it was created by Roger Schank (1972), CD has gone through various incarnations - different sets of primitive actions, different types of states, and different theories of inference. We'll consider a cleaned-up, "canonical" CD theory which is fairly close to Schank's original conception but includes a cleaned-up theory of states, relations, and inferences.
At its core, CD is a theory of how to represent sentences. It has two basic axioms:
From these axioms, Schank built a theory based on a primary set of conceptualizations, which come in two kinds: active and stative.
Additionally, there are relationships between states, including static links which are used to define the meaning of sentences, and causal links which can be used to infer new CDs:
This breakdown does not precisely match original CD theory, but it explains the core concepts well enough for our purposes. Now, on to defining actual CDs…
In order to represent identical meanings in an identical way, CD theory breaks actions down in two fashions: a core set of primitive acts which define the basic types of actions that occur, and a set of conceptual cases that add meaning to the basic action types.
While the canonical list of primitive acts has changed as CD theory has evolved, the original core set was:
However, these actions mean almost nothing by themselves. They must be augmented by conceptual cases that define how each action is played out with respect to the actor, the object of the action, the direction of the action, and so on …
These are the "canonical" list of slots for an action; only MTRANS and MBUILD have different slots (an MOBJECT rather than an OBJECT). The remaining sections of this handout show how to build complex meanings out of these primitive actions, their conceptual cases, and an associated list of states.
ATRANS refers to a transfer of possession - the abstract transfer of possession from one person to another, as in a give or a buy. No physical transfer need take place; the transfer occurs purely on the plane of ownership.
Example: "John gave his house to his son."
(ATRANS (ACTOR JOHN)
(OBJECT HOUSE)
(FROM JOHN)
(TO SON)
(TIME PAST))
The primary state associated with ATRANS is POSSESS:
Example: "John's son has the house. "
(POSSESS (OBJECT HOUSE)
(VALUE SON))
(Technically, we could also specify a TIME for POSSESS, but we'll omit that for simplicity.)
PTRANS refers to a transfer of physical location - some object moves from place to place, as in a go or a move. Ownership need not transfer;possession - the abstract transfer of possession from one person to another. No physical transfer need take place; the transfer occurs purely on the plane of ownership.
Example: "Bob hands his wedding ring to the jeweler. "
(PTRANS (ACTOR BOB)
(OBJECT WEDDING_RING)
(FROM BOB)
(TO JEWELER)
(TIME PRESENT))
The primary state associated with PTRANS is AT-LOC.
Example: "The ring is at the jeweler's. "
(AT-LOC (OBJECT WEDDING_RING)
(VALUE JEWELER))
MTRANS refers to the transmission of an IDEA - some conceptualization is transmitted from one head to another (or within the same head). Tell, forget and remember can all be expressed with MTRANS. An idea is represented by an MOBJECT slot in CD, which is superficially like OBJECT except that it contains a whole concept as its value:
Example: "Bob told John that his wedding ring was at the jeweler's. "
(MTRANS (ACTOR BOB)
(MOBJECT (AT-LOC (OBJECT WEDDING_RING)
(VALUE JEWELER)))
(FROM BOB)
(TO JOHN)
(TIME PAST))
Frequently, we want to make a distinction between a person's memory (the LTM) and their central processor (CP) to allow us to discuss remembering and forgetting:
Example: "John forgot that Bob's wedding ring was at the jeweler's. "
(MTRANS (ACTOR JOHN)
(MOBJECT (AT-LOC (OBJECT WEDDING_RING)
(VALUE JEWELER)))
(FROM LTM)
(TO ?location)
(TIME PAST))
Example: "Bob remembered that his wedding ring was at the jeweler's. "
(MTRANS (ACTOR BOB)
(MOBJECT (AT-LOC (OBJECT WEDDING_RING)
(VALUE JEWELER)))
(FROM LTM)
(TO CP)
(TIME PAST))
MOVE refers to the movement of a body part, not the movement of an object. Normally MOVE is instrumental to some other action (such as a kick or a throw), but sometimes it is used by itself, as in kiss, raise a hand, and scratch.
Example: "Bob raised his hand. "
(MOVE (ACTOR BOB)
(OBJECT HAND)
(FROM LOWERED)
(TO RAISED)
(TIME PAST))
The primary state associated with MOVE is POSITION.
Example: "Bob's hand is raised. "
(POSITION (OBJECT HAND)
(VALUE RAISED))
PROPEL refers to the application of force to an object. Normally PROPEL is instrumental to some other action, but sometimes it is used by itself. PROPEL verbs include pushing, pulling, throwing and kicking.
Example: "Bob threw the ball. "
(PROPEL (ACTOR BOB)
(OBJECT BALL)
(FROM BOB)
(TO ?location)
(TIME PAST))
The primary state associated with PROPEL is AT-LOC; generally the PROPEL will also be associated with a PTRANS that allows us to deduce the location.
Example: "Bob threw the ball to Bill."
(PTRANS (ACTOR BOB)
(OBJECT BALL)
(FROM BOB)
(TO BILL)
(TIME PAST)
(INSTRUMENT (PROPEL (ACTOR BOB)
(OBJECT BALL)
(FROM BOB)
(TO BILL)
(TIME PAST)))
GRASP refers to the gripping of some object by a person. Normally GRASP is instrumental to some other action, but sometimes it is used by itself. Note that FROM and TO in general have little meaning with respect to GRASP. GRASP verbs include hold, grab, grasp and let go.
Example: "Bob picked up the ball. "
(GRASP (ACTOR BOB)
(OBJECT BALL))
(TIME PAST))
INGEST refers to a person taking something inside his or her body: eating, drinking, breathing, etc.
Example: "Bob ate an apple. "
(INGEST (ACTOR BOB)
(OBJECT APPLE)
(FROM OUTSIDE-BOB)
(TO INSIDE-BOB)
(TIME PAST))
EXPEL refers to a person taking something outside his or her body: spitting, crying, sweating, etc.
Example: "Bob spat out the seeds. "
(EXPEL (ACTOR BOB)
(OBJECT APPLESEEDS)
(FROM INSIDE-BOB)
(TO OUTSIDE-BOB)
(TIME PAST))
ATTEND refers to a person attending or focusing a sense organ towards a stimulus - look, listen, feel, and so on.
Example: "Mary saw John. "
(ATTEND (ACTOR MARY)
(OBJECT EYE)
(FROM ?location)
(TO JOHN)
(TIME PAST))
SPEAK is an instrumental action that refers to the production of sound: say, play music, scream, and so on.
Example: "Mary screamed."
(SPEAK (ACTOR MARY)
(OBJECT SCREAM)
(TIME PAST))
MBUILD refers to the construction of a mental concept: realize, decide, imagine, conclude, etc. MBUILD frequently uses ATTEND as an instrumental action.
Example: "Mary saw John and realized he was in New York."
(MBUILD (ACTOR MARY)
(MOBJECT (AT-LOC (OBJECT JOHN)
(VALUE NY)))
(FROM ?no-location)
(TO CP)
(INSTRUMENT (ATTEND (ACTOR MARY)
(OBJECT EYE)
(FROM ?past-location)
(TO JOHN)
(TIME PAST)))
(TIME PAST))
DO catches all the things that the first 11 primitive actions don't. It's also useful when we know something happened, but we don't precisely know what or how:
Example: "John fertilized the plants. "
(DO (ACTOR JOHN)
(OBJECT FERTILIZER)
(FROM ?location)
(TO PLANTS))
There is no set of "core states" in CD; states are an open set that can be continually added to. States share a common format, however: an OBJECT is in a STATE with some VALUE. Many states, such as HEALTH, have VALUES that range from -10 to 10; other states, such as AT-LOC, have discrete VALUES such as ATLANTA and NEW_YORK.
Some prominent states include:
Example: "Mary is alive."
(HEALTH (OBJECT MARY)
(VALUE +10))
Example: "John is unconscious."
(MENTAL-STATE (OBJECT JOHN)
(VALUE -10))
Example: "John is depressed."
(EMOTIONAL-STATE (OBJECT JOHN)
(VALUE -5))
Example: "John is in New York."
(AT-LOC (OBJECT JOHN)
(VALUE NEW_YORK))
Example: "John owns the book."
(POSSESS (OBJECT BOOK)
(VALUE JOHN))
Example: "Mr. Spock has the conn."
(CONTROL (OBJECT ENTERPRISE)
(VALUE SPOCK))
Example: "Voyager has been destroyed."
(FUNCTIONALITY (OBJECT VOYAGER)
(VALUE -10))
Example: "Bo knows nonlinear dynamics."
(KNOWS (OBJECT BO)
(VALUE NONLINEAR-DYNAMICS))
We will distinguish two kinds of static relationships in CD: conceptual-level relations, which are CD conceptualizations in their own right, and case-level relations, in which a CD is attached by a conceptual case to another CD.
There are two primary flavors of conceptual-level relations, CAUSE and BI-CAUSE:
Example: "Bill said something that made Mary listen."
(CAUSE
(SOURCE (SPEAK (ACTOR BILL)
(OBJECT WORDS)))
(TARGET (ATTEND (ACTOR MARY)
(OBJECT EAR)
(FROM ?location)
(TO BILL))))
Example: "John bought a book from Mary."
(BI-CAUSE
(SOURCE (ATRANS (ACTOR MARY)
(OBJECT BOOK)
(FROM MARY)
(TO JOHN)
(TIME PAST)))
(TARGET (ATRANS (ACTOR JOHN)
(OBJECT MONEY)
(FROM JOHN)
(TO MARY)
(TIME PAST))))
There are two primary kinds of conceptual case relationships in CD, INSTRUMENT and MOBJECT:
Example: "Bob threw the ball to Bill."
(PTRANS (ACTOR BOB)
(OBJECT BALL)
(FROM BOB)
(TO BILL)
(TIME PAST)
(INSTRUMENT (PROPEL (ACTOR BOB)
(OBJECT BALL)
(FROM BOB)
(TO BILL)
(TIME PAST)))
Example: "Mary saw John and realized he was in New York."
(MBUILD (ACTOR MARY)
(MOBJECT (AT-LOC (OBJECT JOHN)
(VALUE NY)))
(FROM ?no-location)
(TO CP)
(INSTRUMENT (ATTEND (ACTOR MARY)
(OBJECT EYE)
(FROM ?past-location)
(TO JOHN)
(TIME PAST)))
(TIME PAST))
Unlike relationships, which are required to define the meaning of certain sentences but don't tell us much more about an action, a causal type allows us to infer certain things about existing sentences. (A causal type can also be used to define the meaning of a sentence, as we'll see in a second.) There are four primary types of causal relations:
(RESULT (SOURCE (AT-LOC (OBJECT ?actor)
(VALUE ?location)))
(TARGET (PTRANS (OBJECT ?actor)
(OBJECT ?actor)
(FROM ?location)
(TO ?unknown))))
(RESULT (TARGET (PTRANS (OBJECT ?actor)
(OBJECT ?actor)
(FROM ?dont-care)
(TO ?location)))
(SOURCE (AT-LOC (OBJECT ?actor)
(VALUE ?location))))
Example: "When John came to New York, Mary realized he was there. "
(INITIATES (SOURCE (PTRANS (ACTOR JOHN)
(OBJECT JOHN)
(FROM ?location)
(TO NY)))
(TARGET (MBUILD (ACTOR MARY)
(MOBJECT (AT-LOC (OBJECT JOHN)
(VALUE NY)))
(FROM ?no-location)
(TO CP))))
Note this example is subtly different from our earlier example where Mary saw John; here we don't have that information, but we can still build the relationship.
Example: "When Mary realized John had come to New York, she screamed."
(REASON (SOURCE (MBUILD (ACTOR MARY)
(MOBJECT (AT-LOC (OBJECT JOHN)
(VALUE NY)))
(FROM ?no-location)
(TO CP))))
(TARGET (SPEAK (ACTOR MARY)
(OBJECT SCREAM))))
Here Mary's mental realization prompts a perfectly reasonable physical action.
At many points during this discussion, we left out detail in sentences. States did not show time; actions did not always show instruments; and so on. Which is a pity, because many complex sentences really need five or six CD's to represent them properly. But that level of detail isn't necessary to illustrate the main points of CD, so we won't be that cruel.
For the assignments, unless otherwise indicated, you should not have to represent CD's to more than one level of nesting (a BI-CAUSE with two ATRANSes, a MBUILD with an MOBJECT or INSTRUMENT, and so on). Use only the predefined primitive ACTs and stick to the standard conceptual cases (ACTOR OBJECT MOBJECT TO FROM INSTRUMENT, and TIME), but feel free to create new states if absolutely necessary. Remember that CD states are represented by STATE-OBJECT-VALUE case triples; don't invent new cases for the states.
If you have any questions, please feel free to ask the TA's, or to check out one of the papers or books in the Additional Readings section for further information.
Schank, R. (1972). Conceptual dependency: A theory of natural language understanding. Cognitive Psychology 3 (4): 552-631.
Schank, R. and Abelson, R. (1972). Scripts, Plans, Goals, and Understanding. Lawrence Erlbaum Associates.
Schank, R. and Riesbeck, C.K. (1972). Inside Computer Understanding. Lawrence Erlbaum Associates.